Patent Publication Number: US-2022214527-A1

Title: Lens system, imaging module, and electronic device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a national stage, filed under 35 U.S.C. § 371, of International Application No. PCT/CN2020/079526, filed on Mar. 16, 2020, and entitled “LENS SYSTEM, IMAGING MODULE, AND ELECTRONIC DEVICE”, the content of which is incorporated herein in entirety by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of optical imaging technologies, and more particularly, to a lens system, an imaging module, and an electronic device. 
     BACKGROUND 
     In recent years, with the development of science and technology, periscopic mobile phone lenses are increasingly used in portable electronic products. The periscopic mobile phone lens has a prism part that can change a transmission direction of an optical path, and the lens can be transversely arranged in a housing of the electronic product during mounting, so that the transverse length and overall height of the lens are reduced, thereby achieving a light and thin mobile phone. 
     However, under the development trend of becoming thinner and lighter for the electronic products, it is still difficult for conventional periscopic lenses to achieve a long focal length or an ultra-long focal length. 
     SUMMARY 
     According to various embodiments of the present disclosure, a lens system is provided. 
     A lens system includes a plurality of optical elements arranged along a folded optical axis of the lens system, and the plurality of optical elements includes sequentially from an object side to an image side: 
     a first optical path folding element, located on a first part of the folded optical axis, the first optical path folding element being configured to direct light from the first part of the folded optical axis to a second part of the folded optical axis; 
     a lens group, located on the second part of the folded optical axis; 
     a second optical path folding element, configured to direct light from the second part of the folded optical axis to a third part of the folded optical axis; and 
     a third optical path folding element, configured to direct light from the third part of the folded optical axis to a fourth part of the folded optical axis; 
     where the second part, the third part, and the fourth part of the folded optical axis are located within a same plane, and the plane is perpendicular to the first part of the folded optical axis. 
     An imaging module includes a photosensitive element and the lens system described in the above embodiments. The photosensitive element is disposed on the image side of the lens system. 
     An electronic device includes a housing and the imaging module described in the above embodiment, and the imaging module is mounted on the housing. 
     The details of one or more embodiments of the present disclosure are set forth in the accompanying drawings and description below. Other features, purposes and advantages of the present disclosure will become apparent from the description, the accompanying drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To better describe and illustrate embodiments or examples of the disclosure disclosed herein, reference may be made to one or more accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be construed as limiting the scope of any of the disclosed disclosure, the presently described embodiments or examples, and the presently understood preferred mode of the disclosure. 
         FIG. 1  shows a schematic top view of a lens system according to Embodiment 1 of the present disclosure. 
         FIG. 2  shows a schematic front view of the lens system according to Embodiment 1. 
         FIG. 3  shows a schematic view of a lens group according to Embodiment 1. 
         FIG. 4  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 1, respectively. 
         FIG. 5  shows a schematic top view of a lens system according to Embodiment 2 of the present disclosure. 
         FIG. 6  shows a schematic front view of the lens system according to Embodiment 2. 
         FIG. 7  shows a schematic view of a lens group according to Embodiment 2. 
         FIG. 8  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 2, respectively. 
         FIG. 9  shows a schematic top view of a lens system according to Embodiment 3 of the present disclosure. 
         FIG. 10  shows a schematic front view of the lens system according to Embodiment 3. 
         FIG. 11  shows a schematic view of a lens group according to Embodiment 3. 
         FIG. 12  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 3, respectively. 
         FIG. 13  shows a schematic top view of a lens system according to Embodiment 4 of the present disclosure. 
         FIG. 14  shows a schematic front view of the lens system according to Embodiment 4. 
         FIG. 15  shows a schematic view of a lens group according to Embodiment 4. 
         FIG. 16  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 4, respectively. 
         FIG. 17  shows a schematic top view of a lens system according to Embodiment 5 of the present disclosure. 
         FIG. 18  shows a schematic front view of the lens system according to Embodiment 5. 
         FIG. 19  shows a schematic view of a lens group according to Embodiment 5. 
         FIG. 20  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 5, respectively. 
         FIG. 21  shows a schematic top view of a lens system according to Embodiment 6 of the present disclosure. 
         FIG. 22  shows a schematic front view of the lens system according to Embodiment 6. 
         FIG. 23  shows a schematic view of a lens group according to Embodiment 6. 
         FIG. 24  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 6, respectively. 
         FIG. 25  shows a schematic top view of a lens system according to Embodiment 7 of the present disclosure. 
         FIG. 26  shows a schematic front view of the lens system according to Embodiment 7. 
         FIG. 27  shows a schematic view of a lens group according to Embodiment 7. 
         FIG. 28  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 7, respectively. 
         FIG. 29  shows a schematic top view of a lens system according to Embodiment 8 of the present disclosure. 
         FIG. 30  shows a schematic front view of the lens system according to Embodiment 8. 
         FIG. 31  shows a schematic view of a lens group according to Embodiment 8. 
         FIG. 32  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 8, respectively. 
         FIG. 33  shows a schematic top view of a lens system according to Embodiment 9 of the present disclosure. 
         FIG. 34  shows a schematic front view of the lens system according to Embodiment 9. 
         FIG. 35  shows a schematic view of a lens group according to Embodiment 9. 
         FIG. 36  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 9, respectively. 
         FIG. 37  shows a schematic top view of a lens system according to Embodiment 10 of the present disclosure. 
         FIG. 38  shows a schematic front view of the lens system according to Embodiment 10. 
         FIG. 39  shows a schematic view of a lens group according to Embodiment 10. 
         FIG. 40  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 10, respectively. 
         FIG. 41  shows a schematic top view of a lens system according to Embodiment 11 of the present disclosure. 
         FIG. 42  shows a schematic front view of the lens system according to Embodiment 11. 
         FIG. 43  shows a schematic view of a lens group according to Embodiment 11. 
         FIG. 44  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system according to Embodiment 11, respectively. 
         FIG. 45  shows a schematic view of an imaging module according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     To make the purposes, technical solutions and advantages of the present disclosure to be more apparent and understandable, reference will be made to the accompanying drawings and embodiments to describe the present disclosure in detail below. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and not intended to limit the present disclosure. 
     It should be understood that when an element is defined as “disposed” on another element, it is either directly on an element or indirectly on an element with a mediating element. When an element is considered to be “connected” to another element, it may be directly connected to another element or there may be an intermediate element between them at the same time. The terms “vertical”, “horizontal”, “left”, “right”, and the like used herein are for illustrative purposes only and are not intended to be the only embodiment. 
     All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure applies, unless otherwise defined. The terms used in the specification of present disclosure herein are for the purpose of describing specific embodiments only and are not intended to limit the present disclosure. The term “and/or” used herein includes any and all combinations of one or more of the associated listed items. 
     In this specification, expressions such as first, second, third, and the like, are merely used to distinguish one feature from another feature, and do not indicate any limitations on the features. Therefore, without departing from the teachings of the present disclosure, the first lens discussed below may also be referred to as a second lens or a third lens. To facilitate the description, the shapes of the spherical surfaces or aspherical surfaces shown in the drawings are shown by way of example. That is, the shapes of the spherical surfaces or the aspherical surfaces are not limited to the shapes of the spherical surfaces or the aspherical surfaces shown in the drawings. The accompanying drawings are only examples and are not drawn strictly to scale. 
     In this specification, a space on a side where an object is located relative to an optical element is referred to as an object side of the optical element, and correspondingly, a space on a side where an image imaged by the object is located relative to the optical element is referred to as an image side of the optical element. A surface of each lens closest to the object is called an object side surface, and a surface of each lens closest to the imaging plane is called an image side surface. 
     In addition, in the description hereinafter, if a surface of the lens is convex and the convex position is not defined, it means that this surface of the lens is convex at least at the paraxial area. If a surface of the lens is concave and the concave position is not defined, it means that this surface of the lens is concave at least at the paraxial area. The paraxial area here refers to an area near the optical axis. 
     The conventional periscopic lens usually uses one or two reflective prisms to realize the folding of the optical path. However, if the focal length of this type of lens is made longer, it is easy to increase the thickness of the mobile phone or to cause the total length of the lens itself become longer, which affects the arrangement of other elements of the mobile phone. Therefore, the focal length of the conventional periscopic lens is usually not long, and it is difficult to meet the user&#39;s higher demand for long-distance zoom shooting. 
     The defects of the above solutions are results obtained by the inventors through practice and careful research. Therefore, the discovery process of the above problems and the solutions proposed in the embodiments of the present disclosure for the above problems below should be regarded as the inventors&#39; contributions to the present disclosure during the process of the present disclosure. 
     A lens system according to the embodiments of the present disclosure includes a plurality of optical elements arranged along a folded optical axis thereof. The above plurality of optical elements include, sequentially arranged from an object side to an image side, a first optical path folding element, a lens group, a second optical path folding element, and a third optical path folding element. 
     The first optical path folding element is located on a first part of the folded optical axis, and the first optical path folding element is configured to direct light from the first part of the folded optical axis to a second part of the folded optical axis. The lens group is located on the second part of the folded optical axis. The second optical path folding element is configured to direct light from the second part of the folded optical axis to a third part of the folded optical axis. The third optical path folding element is configured to direct light from the third part of the folded optical axis to a fourth part of the folded optical axis. Finally, the light rays are received by a photosensitive element located on the fourth part of the folded optical axis. 
     The second part, the third part, and the fourth part of the folded optical axis are located in one same plane, and this plane is perpendicular to the first part of the folded optical axis. 
     The above lens system can allow the above plurality of optical elements to be arranged along a transverse direction of the electronic product, instead of being arranged along a thickness direction of the electronic equipment, so that the lens can achieve a long focal length while ensuring that the electronic product is light and thin. In addition, by folding the optical axis of the lens system, the transverse total length of the lens system can be effectively shortened, thereby saving the transverse space of the electronic product and facilitating the arrangement of other elements in the electronic product. 
     Specifically, the optical folding element may be a prism. The prism includes a light incident surface, a reflective surface, and a light emergent surface. Light rays are incident from the light incident surface, are totally reflected on the reflective surface, and then are emitted from the light emergent surface, thereby completing the folding of the optical path. Further, the prism may be a right-angle prism, so that the light rays can be turned 90°, which is convenient for adjusting the folding path of the light rays in the lens system. 
     Taking a lens system  10  shown in  FIGS. 1 to 3  as an example, the lens system  10  includes a first right-angle prism P 1 , a lens group  100 , a second right-angle prism P 2 , and a third right-angle prism P 3  arranged along its folded optical axis. A light incident surface S 1  of the first right-angle prism P 1 , a light incident surface S 12  of the second right-angle prism P 2 , and a light incident surface S 15  of the third right-angle prism P 3  are perpendicular to each other. A light emergent surface S 3  of the first right-angle prism P 1  is perpendicular to a light emergent surface S 14  of the second right-angle prism P 2 , and the light emergent surface S 3  of the first right-angle prism P 1  is parallel to a light emergent surface S 17  of the third right-angle prism P 3 , so that a first part AX 1  (that is, the X direction in the figures) of the folded optical axis is perpendicular to a plane where a second part AX 2 , a third part AX 3 , and a fourth part AX 4  of the folded optical axis are located. Therefore, after being incident along the optical axis AX 1 , light rays can be sequentially re-directed to the optical axis AX 2 , the optical axis AX 3 , and the optical axis AX 4 , so as to achieve a long focal length. In addition, the third right-angle prism P 3  can also be prevented from being arranged along the thickness direction (that is, the direction of the optical axis AX 1  in  FIG. 1 ) of the electronic product, so as to meet the development trend of becoming lighter and thinner for the electronic products. 
     In an exemplary embodiment, the lens group includes, sequentially arranged from the object side to the image side along the second part of the folded optical axis, a first lens having a refractive power, a second lens having a refractive power, and a third lens having a refractive power. An object side surface and/or an image side surface of at least one lens of the first lens to the third lens are aspherical, and at least one surface of the object side surface and the image side surface of the at least one lens has at least one inflection point. 
     By arranging an appropriate number of lenses in the lens group and reasonably distributing the refractive power, surface shape, and effective focal length of each of the lenses, the imaging resolution capability of the lens system can be enhanced and aberrations can be effectively corrected. In addition, by configuring the surface of the lens as an aspherical surface, the flexibility of lens design can be improved, so as to further correct the aberrations. Moreover, the inflection point can further be arranged on the aspherical surface, so that the incident angle of the chief ray can be better matched with the photosensitive element, thereby improving the imaging quality of the lens system. 
     In some other embodiments, the object side surfaces and the image side surfaces of the lenses of the lens group may also be all spherical surfaces. It should be noted that the above embodiments are merely examples of some embodiments of the present disclosure. In some embodiments, the surfaces of the lenses in the lens group may be any combination of aspherical surface or spherical surface. 
     Further, an optical stop is further provided in the lens group, and the optical stop is arranged on the object side of the lens group, that is, between the first optical path folding element and the first lens, so as to better control the size of the incident light beam and improve the imaging quality of the lens system. Specifically, the optical stop includes an aperture stop and a field stop. Preferably, the optical stop is an aperture stop. The aperture stop can be located on a surface (for example, the object side surface and the image side surface) of the lens, and form a functional relationship with the lens. For example, an aperture stop can be formed on the surface by coating a light-blocking coating layer on a surface of the lens; or, a surface of the lens is fixedly clamped by a clamping piece, and the structure of the clamping piece located on the surface can limit a width of an imaging light beam of an on-axis object point, thereby forming an aperture stop on the surface. 
     When the above described lens system is used for imaging, light rays emitted or reflected by a subject enter the lens system from the object side, and sequentially pass through the first optical path folding element, the first lens, the second lens, the third lens, the second optical path folding element, and the third optical path folding element, and finally converge onto the imaging plane. 
     In an exemplary embodiment, the lens system satisfies the following relation: 3 mm&lt;f/FNO&lt;12 mm; where, f represents an effective focal length of the lens system, and FNO represents an f-number of the lens system. f/FNO may be 3.5 mm, 4 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, 10.5 mm, or 11 mm Under the condition that the above relation is satisfied, an entrance pupil diameter of the lens system can be effectively adjusted, thereby effectively limiting the overall width of the lens system, which is conducive to the miniaturization of the lens group and saves the space of the electronic product. When f/FNO is less than or equal to 3, the entrance pupil diameter of the system is reduced, and the amount of light entering is reduced, which will easily lead to darkening of the image and reduced clarity of the image, which is not conducive to imaging. When f/FNO is greater than or equal to 12, the entrance pupil diameter of the system is relatively large, which is not conducive to reducing the width of the system, making the system occupy a larger space. 
     In an exemplary embodiment, the lens system satisfies the following relation: HFOV/TTL&gt;0.1 degrees/mm; where, HFOV represents a half field of view of the lens system in a diagonal direction, and TTL represents a distance on the optical axis from an object side surface of the first lens to the imaging plane of the lens system. HFOV/TTL may be 0.15, 0.17, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3 or 0.35, in a unit of degrees/mm Under the condition that HFOV/TTL satisfies the above relation, the image height of the imaged image and the total length of the lens system can be reasonably allocated, which is conducive to shortening the total length of the lens system and achieving the miniaturization. When HFOV/TTL is less than or equal to 0.1, the total length of the system is larger and the field of view is smaller, which tends to degrade the image quality. 
     In an exemplary embodiment, the lens system satisfies the following relation: TTL/f&lt;1.2; where, TTL represents a distance on the optical axis from the object side surface of the first lens to the imaging plane of the lens system, and f represents the effective focal length of the lens system. TTL/f may be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1.0. Under the condition that the above relation is satisfied, the effective focal length of the lens system and the total length of the lens system can be reasonably allocated, so that not only the miniaturization of the lens system can be realized, but also the light rays can be better focused on the imaging plane, and the imaging quality can be improved. When TTL/f is greater than or equal to 1.2, the total length of the system is longer, which is not conducive to miniaturization. 
     In an exemplary embodiment, the lens system satisfies the following relation: f&gt;15 mm; where f is the effective focal length of the lens system. f may be 20 mm, 23 mm, 25 mm, 27 mm, 29 mm, 31 mm, 33 mm, 35 mm, 37 mm, or 40 mm Under the condition that the above relation is satisfied, the lens system can have a characteristic of a long focal length, so that clear imaging of a distant object can be realized. When f is less than or equal to 15 mm, the focal length is relatively short, and the long-distance shooting capability of the lens system is not high. 
     In an exemplary embodiment, the lens system satisfies the following relation: CT12/CT23&lt;3; where, CT12 represents a distance on the optical axis from an image side surface of the first lens to an object side surface of the second lens, and CT23 represents a distance on the optical axis from an image side surface of the second lens to an object side surface of the third lens. CT12/CT23 may be 0.02, 0.03, 0.06, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 2.5, 2.9 or 2.95. Under the condition that the above relation is satisfied, it is conducive to correcting the aberration of the lens system and control the degree of the curvature of field of the lens system, thereby improving the imaging quality. When CT12/CT23 is greater than or equal to 3, a distance between the first lens and the second lens is relatively far, and the second lens and the third lens are relatively close to each other, which is not conducive to correcting the aberrations of the system and controlling the curvature of field, and tends to affect the imaging quality. 
     In an exemplary embodiment, the lens system satisfies the following relation: 2.2&lt;FNO&lt;6.8; where, FNO represents the f-number of the lens system. FNO may be 2.3, 2.5, 3, 3.3, 3.6, 3.9, 4.5, 4.9, 5.2, 5.5, 6, or 6.5. Under the condition that the above relation is satisfied, the amount of light passing through the lens system can be increased, thereby reducing the aberration of the edge field of view of the system, and in addition, the lens system can also obtain clear and detailed information of the subject even in a relatively dark environment or in the case of insufficient light rays, thereby improving the image quality. When FNO is less than or equal to 2.2, it is easy to cause the depth of field of the system to be small, which is not conducive to the clear presentation of the details of the object. 
     In an exemplary embodiment, the lens system satisfies the following relation: D32/ImgH&lt;1.3; where D32 represents an effective half clear aperture of the third lens, and ImgH represents half of a diagonal length of an effective pixel area on the imaging plane of the lens system. D32/ImgH may be 0.5, 0.9, 1, 1.05, 1.1, 1.12, 1.14, 1.16, 1.18, 1.2, 1.25, 1.28, or 1.29. Under the condition that the above relation is satisfied, the size of the lens group can be effectively limited, which is conducive to realize the ultra-thinness of the lens system, and meets the development needs of light and thin electronic products. When D32/ImgH is greater than or equal to 1.3, the effective half clear aperture of the third lens is relatively large, which does not meet the application needs of light and thin electronic products. 
     In an exemplary embodiment, the lenses in the lens group may be all made of glass or all made of plastic. The plastic lenses can reduce the weight of the lens system and reduce the production cost, while the glass lenses can make the lens system have relatively good temperature tolerance characteristics and excellent optical performance. Further, when the lens system is applied to portable electronic equipment such as mobile phones and tablets, the lenses are preferably made of plastic. It should be noted that the lenses in the lens group can also be made of any combination of glass and plastic, and not necessarily be all made of glass or all made of plastic. 
     In an exemplary embodiment, the lens group further includes an infrared filter. The infrared filter is arranged between the third lens and the second optical path folding element to filter incident light rays, specifically to isolate infrared light and prevent infrared light from being absorbed by the photosensitive element, thereby avoiding infrared light from affecting the color and clarity of normal images, and improving the imaging quality of the lens system. 
     The lens group of the above described embodiments of the present disclosure may use a plurality of lenses, for example, three lenses as described above. By reasonably distributing the focal lengths, refractive powers, surface shapes, thicknesses of the lenses, and on-axis distances among the lenses, it is possible to ensure that the above lens system has a long focal length, while the system has relatively small total length and is relatively light in weight, and has relatively high imaging quality, which can better meet the application needs of lightweight electronic equipment such as mobile phones, tablets, and the like. However, it should be appreciated by those skilled in the art that without departing from the technical solution claimed in the present disclosure, the number of lenses constituting the lens group can be changed to obtain the various results and advantages described in this specification. 
     Specific embodiments of the lens system applicable to the above described embodiments will be further described below with reference to the accompanying drawings. 
     Embodiment 1 
     A lens system  10  of Embodiment 1 of the present disclosure will be described below with reference to  FIGS. 1 to 4 . 
     As shown in  FIGS. 1 to 3 , the lens system  10  includes, sequentially arranged from an object side to an image side along a folded optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . Further, Y-Z coordinate axes are provided in  FIG. 1 , and Y-X coordinate axes are provided in  FIG. 2 , where, the optical axis AX 1  is parallel to the X axis, the optical axis AX 3  is parallel to the Y axis, and the optical axis AX 2  and the optical axis AX 4  are parallel to the Z axis. 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a negative refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is concave at the optical axis and is convex at its circumference, and the image side surface S 5  is concave at the optical axis and is concave at its circumference. The second lens L 2  has a positive refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is concave at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a positive refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is convex at the optical axis and is convex at its circumference, and the image side surface S 9  is convex at the optical axis and is concave at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     Light rays can be folded by the reflective surfaces of the right-angle prisms by 90° and then are emitted, so as to achieve a long focal length while shortening the transverse total length of the system. In this embodiment, the light rays are incident along the optical axis AX 1  (that is, the X-axis direction), and then are reflected by the reflective surface S 2  of the first right-angle prism P 1  to be folded by 90°, and directed to the optical axis AX 2  (that is, the Z-axis direction) and projected to the lens group  100 . After being emitted from the lens group  100 , the light rays are further reflected by the reflective surface S 13  of the second right-angle prism P 2  to be folded by 90°, and directed to the optical axis AX 3  (that is, the Y-axis direction). Finally, the light rays are reflected by the reflective surface S 16  of the third right-angle prism P 3  to be folded by 90°, and directed to the optical axis AX 4  (that is, the Z-axis direction), so as to be received by a photosensitive element (not shown in the figure) disposed on the optical axis AX 4 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are configured to be aspherical, which is conducive to correcting aberrations and solving the problem of distortion of the image plane, and can also enable the lens to achieve good optical imaging effects even when the lenses are small, thin, and flat, thereby enabling the lens system  10  to have a characteristic of miniaturization. 
     The first lens L 1  to the third lens L 3  are all made of plastic, so as to reduce the weight of the lens system  10  and reduce the production cost. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1  to limit the size of the incident light beam and further improve the imaging quality of the lens system  10 . The lens system  10  further includes a filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . Light from the object OBJ sequentially passes through the respective surfaces S 1  to S 17  and is finally imaged on the imaging plane S 18 . Further, the filter  110  is an infrared filter, which is configured to filter infrared light rays from external light rays incident on the lens system  10  to avoid color distortion of the image. Specifically, the filter  110  is made of glass. 
     Table 1 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient) of each of the optical elements and effective focal lengths of lenses of the lens system  10  according to Embodiment 1, where the units of the radius of curvature, the thickness, the effective focal length of the lens, Y-half aperture (effective half clear aperture in the Y-direction of the lens), and X-half aperture (effective half clear aperture in the X-direction of the lens) are all millimeters (mm) In addition, taking the first right-angle prism P 1  as an example, it is default that a direction facing inward the page and perpendicular to the page is the positive direction of the optical axis AX 1 , and a direction facing outward the page and perpendicular to the page is the negative direction of the optical axis AX 1 . Taking the first lens L 1  as an example, the first value of the first lens L 1  in the “thickness” parameter column is a thickness of the lens on the optical axis AX 2 , and the second value therein is a distance on the optical axis AX 2  from an image side surface of the lens to an object side surface of a lens that is subsequent in a direction towards the image side. It is default that a direction from the object side surface S 4  of the first lens L 1  to the image side surface S 9  of the third lens L 3  is the positive direction of the optical axis AX 2 . The value of the optical stop STO in the “thickness” parameter column is a distance on the optical axis AX 2  from the optical stop STO to a vertex of the object side surface of the subsequent lens (the vertex refers to an intersection of the lens and the optical axis). When this value is negative, it means that the optical stop STO is disposed on the right side of the vertex of the object side surface of the lens, and when the thickness of the optical stop STO is positive, the optical stop is on the left side of the vertex of the object side surface of the lens Taking the second right-angle prism P 2  and the third right-angle prism P 3  as an example, a direction from the surface S 14  to the surface S 15  is the negative direction of the optical axis AX 3  Taking the third right-angle prism P 3  as an example, a direction from the surface S 17  to the imaging plane S 18  is the positive direction of the optical axis AX 4 . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Embodiment 1 
               
               
                 f = 20 mm, FNO = 4.9, HFOV = 6.52°, TTL = 18.93 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface 
                 Radius of 
                 Thick- 
                   
                 Refractive 
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 ness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 OBJ 
                 Object 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −2.600 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.600 
                 2.600 
               
               
                 S2 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.600 
                   
                   
                   
                   
                 Reflection 
                 2.600 
                 3.677 
               
               
                 S3 
                   
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 2.600 
                 2.600 
               
               
                 STO 
                 Optical stop 
                 Spherical 
                 Infinite 
                 0.100 
                   
                   
                   
                   
                 Refraction 
                 2.041 
                 2.041 
               
               
                 S4 
                 First lens 
                 Aspherical 
                 −142.561 
                 2.000 
                 Plastic 
                 1.546 
                 56.114 
                 −10.283 
                 Refraction 
                 2.055 
                 2.055 
               
               
                 S5 
                   
                 Aspherical 
                 5.873 
                 0.241 
                   
                   
                   
                   
                 Refraction 
                 2.178 
                 2.178 
               
               
                 S6 
                 Second lens 
                 Aspherical 
                 5.325 
                 3.303 
                 Plastic 
                 1.644 
                 23.517 
                 999.997 
                 Refraction 
                 2.231 
                 2.231 
               
               
                 S7 
                   
                 Aspherical 
                 4.065 
                 0.461 
                   
                   
                   
                   
                 Refraction 
                 2.675 
                 2.675 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 3.997 
                 3.900 
                 Plastic 
                 1.546 
                 56.114 
                 6.237 
                 Refraction 
                 2.961 
                 2.961 
               
               
                 S9 
                   
                 Aspherical 
                 −15.065 
                 1.149 
                   
                   
                   
                   
                 Refraction 
                 2.737 
                 2.737 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.710 
                 2.710 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.590 
                   
                   
                   
                   
                 Refraction 
                 2.707 
                 2.707 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.900 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.900 
                 2.900 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −2.900 
                   
                   
                   
                   
                 Reflection 
                 4.101 
                 2.900 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −1.680 
                   
                   
                   
                   
                 Refraction 
                 2.900 
                 2.900 
               
               
                 S15 
                 Third right- 
                 Spherical 
                 Infinite 
                 −2.900 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.900 
                 2.900 
               
               
                 S16 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.900 
                   
                   
                   
                   
                 Reflection 
                 4.101 
                 2.900 
               
               
                 S17 
                   
                 Spherical 
                 Infinite 
                 8.759 
                   
                   
                   
                   
                 Refraction 
                 2.900 
                 2.900 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                   
                 plane 
               
               
                   
               
            
           
         
       
     
     A surface shape of aspherical surface of each lens is defined by the following equation: 
     
       
         
           
             
               
                 
                   x 
                   = 
                   
                     
                       
                         ch 
                         2 
                       
                       
                         1 
                         + 
                         
                           
                             1 
                             - 
                             
                               
                                 ( 
                                 
                                   k 
                                   + 
                                   1 
                                 
                                 ) 
                               
                               ⁢ 
                               
                                 c 
                                 2 
                               
                               ⁢ 
                               
                                 h 
                                 2 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       Σ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         Aih 
                         i 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Where, x is a distance vector height of the aspherical surface from the vertex of the aspherical surface when the aspherical surface is at a position with a height of h along the optical axis direction; c is a paraxial curvature of the aspherical surface, c=1/R (that is, the paraxial curvature c is a reciprocal of the radius of curvature R shown in Table 1); k is a conic coefficient; and Ai is an i-th order coefficient of the aspherical surface. Table 2 below shows the high-order term coefficients A4, A6, A8, A10, A12, A14, A16, A18, and A20 that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 1. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Embodiment 1 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                 −2.9700E−03 
                 −7.7000E−04 
                   4.9400E−03 
                   2.7800E−03 
                 −2.5300E−03 
                 −2.7200E−03 
               
               
                 A6 
                   1.9000E−04 
                   6.6000E−04 
                   5.9000E−04 
                   1.3400E−03 
                   1.0000E−03 
                 −1.8000E−04 
               
               
                 A8 
                 −1.0000E−05 
                 −1.6000E−04 
                 −1.2000E−04 
                 −1.1000E−04 
                 −8.0000E−05 
                 −1.0000E−05 
               
               
                 A10 
                   0.0000E+00 
                   1.0000E−05 
                   1.0000E−05 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A12 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A18 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     The ImgH which is half of a diagonal length of an effective pixel area on the imaging plane S 18  of the lens system  10  of this embodiment is 2.285 mm. Combining the data in Table 1 and Table 2, it can be seen that the lens system  10  in Embodiment 1 satisfies the following relations. 
     f/FNO=4.082 mm, where, f represents an effective focal length of the lens system  10 , and FNO represents an f-number of the lens system  10 . 
     HFOV/TTL=0.344 degrees/mm, where, HFOV represents a half field of view of the lens system  10  in a diagonal direction, and TTL represents a distance on the folded optical axis from the object side surface S 4  of the first lens L 1  to the imaging plane S 18  of the lens system  10 . 
     TTL/f=0.947, where, TTL represents a distance on the optical axis from the object side surface S 4  of the first lens L 1  to the imaging plane S 18  of the lens system  10 , and f represents the effective focal length of the lens system  10 . 
     f=20 mm, where, f represents the effective focal length of the lens system  10 . 
     CT12/CT23=0.522, where, CT12 represents a distance on the optical axis AX 2  from the image side surface S 5  of the first lens L 1  to the object side surface S 6  of the second lens L 2 , and CT23 represents a distance on the optical axis AX 2  from the image side surface S 7  of the second lens L 2  to the object side surface S 8  of the third lens L 3 . 
     FNO=4.9, where, FNO represents the f-number of the lens system  10 . 
     D32/ImgH=1.198, where, D32 represents an effective half clear aperture of the third lens L 3 , and ImgH represents half of the diagonal length of the effective pixel area on the imaging plane S 18  of the lens system  10 . 
       FIG. 4  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 1, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 4 , it can be seen that the lens system  10  provided in Embodiment 1 can achieve good imaging quality. 
     Embodiment 2 
     A lens system  10  of Embodiment 2 of the present disclosure will be described below with reference to  FIGS. 5 to 8 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 5 to 7 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a negative refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is concave at the optical axis and is concave at its circumference. The second lens L 2  has a negative refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is convex at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a positive refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is convex at the optical axis and is concave at its circumference, and the image side surface S 9  is convex at the optical axis and is convex at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 3 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 2, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 4 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 2, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 5 shows values of relevant parameters of the lens system  10  given in Embodiment 2. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Embodiment 2 
               
               
                 f = 25 mm, FNO = 6.51, HFOV = 5.22°, TTL = 18.01 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface 
                 Radius of 
                 Thick- 
                   
                 Refractive 
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 ness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 OBJ 
                 Object 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −2.150 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.150 
                 2.150 
               
               
                 S2 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.150 
                   
                   
                   
                   
                 Reflection 
                 2.150 
                 3.041 
               
               
                 S3 
                   
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 2.150 
                 2.150 
               
               
                 STO 
                 Optical 
                 Spherical 
                 Infinite 
                 0.100 
                   
                   
                   
                   
                 Refraction 
                 1.920 
                 1.920 
               
               
                   
                 stop 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S4 
                 First lens 
                 Aspherical 
                 10.572 
                 2.112 
                 Plastic 
                 1.546 
                 56.114 
                 −1000.001 
                 Refraction 
                 1.948 
                 1.948 
               
               
                 S5 
                   
                 Aspherical 
                 9.640 
                 0.399 
                   
                   
                   
                   
                 Refraction 
                 1.885 
                 1.885 
               
               
                 S6 
                 Second 
                 Aspherical 
                 5.954 
                 1.960 
                 Plastic 
                 1.644 
                 23.517 
                 −17.016 
                 Refraction 
                 1.953 
                 1.953 
               
               
                 S7 
                 lens 
                 Aspherical 
                 3.360 
                 1.415 
                   
                   
                   
                   
                 Refraction 
                 1.950 
                 1.950 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 25.721 
                 1.117 
                 Plastic 
                 1.546 
                 56.114 
                 9.625 
                 Refraction 
                 2.186 
                 2.186 
               
               
                 S9 
                   
                 Aspherical 
                 −6.502 
                 2.134 
                   
                   
                   
                   
                 Refraction 
                 2.284 
                 2.284 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.284 
                 2.284 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.853 
                   
                   
                   
                   
                 Refraction 
                 2.284 
                 2.284 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.500 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −2.500 
                   
                   
                   
                   
                 Reflection 
                 3.536 
                 2.500 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −2.707 
                   
                   
                   
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S15 
                 Third right- 
                 Spherical 
                 Infinite 
                 −2.500 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S16 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.500 
                   
                   
                   
                   
                 Reflection 
                 3.536 
                 2.500 
               
               
                 S17 
                   
                 Spherical 
                 Infinite 
                 10.518 
                   
                   
                   
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                   
                 plane 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Embodiment 2 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                 −2.1400E−03 
                 −7.6900E−03 
                   4.3000E−04 
                   8.6000E−03 
                 −8.8000E−04 
                 −1.4000E−04 
               
               
                 A6 
                   1.0000E−05 
                   6.9000E−04 
                   1.0600E−03 
                   1.4900E−03 
                   6.5000E−04 
                   2.3000E−04 
               
               
                 A8 
                   0.0000E+00 
                 −1.4000E−04 
                 −1.5000E−04 
                 −2.3000E−04 
                 −3.0000E−05 
                   0.0000E+00 
               
               
                 A10 
                   0.0000E+00 
                   1.0000E−05 
                   1.0000E−05 
                   2.0000E−05 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 Al2 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+30 
               
               
                 Al8 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Embodiment 2 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 25 
                 f/FNO (mm) 
                 3.84 
               
               
                 FNO 
                 6.51 
                 HFOV/TTL (degrees/mm) 
                 0.29 
               
               
                 HFOV (degrees) 
                 5.22 
                 TTL/f 
                 0.72 
               
               
                 TTL 
                 18.01 
                 CT12/CT23 
                 0.282 
               
               
                 ImgH 
                 2.285 
                 D32/ImgH 
                 1 
               
               
                   
               
            
           
         
       
     
       FIG. 8  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 2, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 8 , it can be seen that the lens system  10  provided in Embodiment 2 can achieve good imaging quality. 
     Embodiment 3 
     A lens system  10  of Embodiment 3 of the present disclosure will be described below with reference to  FIGS. 9 to 12 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 9 to 11 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a positive refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is convex at the optical axis and is concave at its circumference. The second lens L 2  has a negative refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is concave at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a positive refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is concave at the optical axis and is concave at its circumference, and the image side surface S 9  is convex at the optical axis and is convex at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 6 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 3, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 7 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 3, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 8 shows values of relevant parameters of the lens system  10  given in Embodiment 3. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Embodiment 3 
               
               
                 f = 29.84 mm, FNO = 5.5, HFOV = 4.370, TTL = 19.94 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface 
                 Radius of 
                 Thick− 
                   
                 Refractive 
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 ness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 OBJ 
                 Object plane 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −3.250 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 3.250 
                 3.250 
               
               
                 S2 
                 angle prism 
                 Spherical 
                 Infinite 
                 3.250 
                   
                   
                   
                   
                 Reflection 
                 3.250 
                 4.596 
               
               
                 S3 
                   
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 3.250 
                 3.250 
               
               
                 STO 
                 Optical stop 
                 Spherical 
                 Infinite 
                 0.080 
                   
                   
                   
                   
                 Refraction 
                 2.713 
                 2.713 
               
               
                 S4 
                 First lens 
                 Aspherical 
                 6.183 
                 2.925 
                 Plastic 
                 1.546 
                 56.114 
                 11.223 
                 Refraction 
                 2.774 
                 2.774 
               
               
                 S5 
                   
                 Aspherical 
                 −559.850 
                 0.100 
                   
                   
                   
                   
                 Refraction 
                 2.390 
                 2.390 
               
               
                 S6 
                 Second lens 
                 Aspherical 
                 7.606 
                 1.787 
                 Plastic 
                 1.644 
                 23.517 
                 −10.338 
                 Refraction 
                 2.337 
                 2.337 
               
               
                 S7 
                   
                 Aspherical 
                 3.223 
                 3.103 
                   
                   
                   
                   
                 Refraction 
                 2.004 
                 2.004 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 −6.965 
                 4.000 
                 Plastic 
                 1.546 
                 56.114 
                 52.000 
                 Refraction 
                 2.026 
                 2.026 
               
               
                 S9 
                   
                 Aspherical 
                 −6.727 
                 1.155 
                   
                   
                   
                   
                 Refraction 
                 2.563 
                 2.563 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.538 
                 2.538 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.689 
                   
                   
                   
                   
                 Refraction 
                 2.536 
                 2.536 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.750 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.750 
                 2.750 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −2.750 
                   
                   
                   
                   
                 Reflection 
                 3.889 
                 2.750 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −1.443 
                   
                   
                   
                   
                 Refraction 
                 2.750 
                 2.750 
               
               
                 S15 
                 Third right- 
                 Spherical 
                 Infinite 
                 −2.650 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.650 
                 2.650 
               
               
                 S16 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.650 
                   
                   
                   
                   
                 Reflection 
                 3.748 
                 2.650 
               
               
                 S17 
                   
                 Spherical 
                 Infinite 
                 7.414 
                   
                   
                   
                   
                 Refraction 
                 2.650 
                 2.650 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                   
                 plane 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Embodiment 3 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A4 
                 −5.1000E−04 
                 −3.8800E−03 
                 −2.1000E−04 
                   5.3900E−03 
                   4.7000E−04 
                 8.0000E−05 
               
               
                 A6 
                 −8.0000E−05 
                   6.7000E−04 
                   1.1500E−03 
                   1.6600E−03 
                   5.1000E−04 
                 6.0000E−05 
               
               
                 A8 
                   0.0000E+00 
                 −1.4000E−04 
                 −1.8000E−04 
                 −2.1000E−04 
                 −2.0000E−05 
                 0.0000E+00 
               
               
                 A10 
                   0.0000E+00 
                   1.0000E−05 
                   1.0000E−05 
                   1.0000E−05 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 Al2 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A14 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A16 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A18 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A20 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
               
                   
               
               
                 Embodiment 3 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 29.84 
                 f/FNO (mm) 
                 5.425 
               
               
                 FNO 
                 5.5 
                 HFOV/TTL (degrees/mm) 
                 0.219 
               
               
                 HFOV (degrees) 
                 4.37 
                 TTL/f 
                 0.668 
               
               
                 TTL 
                 19.94 
                 CT12/CT23 
                 0.032 
               
               
                 ImgH 
                 2.285 
                 D32/ImgH 
                 1.122 
               
               
                   
               
            
           
         
       
     
       FIG. 12  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 3, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 12 , it can be seen that the lens system  10  provided in Embodiment 3 can achieve good imaging quality. 
     Embodiment 4 
     A lens system  10  of Embodiment 4 of the present disclosure will be described below with reference to  FIGS. 13 to 16 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 13 to 15 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a positive refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is concave at the optical axis and is convex at its circumference. The second lens L 2  has a negative refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is concave at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a negative refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is concave at the optical axis and is concave at its circumference, and the image side surface S 9  is convex at the optical axis and is convex at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 9 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 4, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 10 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 4, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 11 shows values of relevant parameters of the lens system  10  given in Embodiment 4. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Embodiment 4 
               
               
                 f = 35.17 mm, FNO = 4.9, HFOV = 3.721°, TTL = 20.80 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                 Refrac- 
                   
                   
                   
                   
                   
               
               
                 Surface 
                 Surface 
                 Surface 
                 Radius of 
                 Thick- 
                   
                 tive 
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 ness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 OBJ 
                 Object 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −4.000 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 4.000 
                 4.000 
               
               
                 S2 
                 angle 
                 Spherical 
                 Infinite 
                 4.000 
                   
                   
                   
                   
                 Reflection 
                 4.000 
                 5.657 
               
               
                 S3 
                 prism 
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 4.000 
                 4.000 
               
               
                 STO 
                 Optical 
                 Spherical 
                 Infinite 
                 0.070 
                   
                   
                   
                   
                 Refraction 
                 3.589 
                 3.589 
               
               
                   
                 stop 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S4 
                 First lens 
                 Aspherical 
                 6.140 
                 3.900 
                 Plastic 
                 1.546 
                 56.114 
                 12.467 
                 Refraction 
                 3.681 
                 3.681 
               
               
                 S5 
                   
                 Aspherical 
                 48.646 
                 0.150 
                   
                   
                   
                   
                 Refraction 
                 2.953 
                 2.953 
               
               
                 S6 
                 Second 
                 Aspherical 
                 8.264 
                 1.483 
                 Plastic 
                 1.644 
                 23.517 
                 −12.921 
                 Refraction 
                 2.858 
                 2.858 
               
               
                 S7 
                 lens 
                 Aspherical 
                 3.855 
                 6.336 
                   
                   
                   
                   
                 Refraction 
                 2.543 
                 2.543 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 −5.337 
                 2.300 
                 Plastic 
                 1.546 
                 56.114 
                 −1017.725 
                 Refraction 
                 2.233 
                 2.233 
               
               
                 S9 
                   
                 Aspherical 
                 −6.208 
                 1.265 
                   
                   
                   
                   
                 Refraction 
                 2.642 
                 2.642 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.598 
                 2.598 
               
               
                 S11l 
                 filter 
                 Spherical 
                 Infinite 
                 0.689 
                   
                   
                   
                   
                 Refraction 
                 2.595 
                 2.595 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.750 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.750 
                 2.750 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −2.750 
                   
                   
                   
                   
                 Reflection 
                 3.889 
                 2.750 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −0.976 
                   
                   
                   
                   
                 Refraction 
                 2.750 
                 2.750 
               
               
                 S15 
                 Third 
                 Spherical 
                 Infinite 
                 −2.600 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.600 
                 2.600 
               
               
                 S16 
                 right-angle 
                 Spherical 
                 Infinite 
                 2.600 
                   
                   
                   
                   
                 Reflection 
                 3.677 
                 2.600 
               
               
                 S17 
                 prism 
                 Spherical 
                 Infinite 
                 5.446 
                   
                   
                   
                   
                 Refraction 
                 2.600 
                 2.600 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                   
                 plane 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Embodiment 4 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                 −1.5000E−04 
                 −2.5300E−03 
                   4.5000E−04 
                   4.2600E−03 
                   2.0900E−03 
                   9.7000E−04 
               
               
                 A6 
                 −3.0000E−05 
                   7.4000E−04 
                   1.2500E−03 
                   1.2500E−03 
                   7.2000E−04 
                   2.0000E−04 
               
               
                 A8 
                   0.0000E+00 
                 −1.4000E−04 
                 −1.8000E−04 
                 −1.7000E−04 
                 −1.0000E−04 
                 −2.0000E−05 
               
               
                 A10 
                   0.0000E+00 
                   1.0000E−05 
                   1.0000E−05 
                   1.0000E−05 
                   1.0000E−05 
                   0.0000E+00 
               
               
                 A12 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A18 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 11 
               
               
                   
               
               
                 Embodiment 4 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 35.17 
                 f/FNO (mm) 
                 7.177 
               
               
                 FNO 
                 4.9 
                 HFOV/TTL (degrees/mm) 
                 0.179 
               
               
                 HFOV (degrees) 
                 3.721 
                 TTL/f 
                 0.592 
               
               
                 TTL 
                 20.8 
                 CT12/CT23 
                 0.024 
               
               
                 ImgH 
                 2.285 
                 D32/ImgH 
                 1.156 
               
               
                   
               
            
           
         
       
     
       FIG. 16  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 4, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 16 , it can be seen that the lens system  10  provided in Embodiment 4 can achieve good imaging quality. 
     Embodiment 5 
     A lens system  10  of Embodiment 5 of the present disclosure will be described below with reference to  FIGS. 17 to 20 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 17 to 19 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a negative refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is concave at the optical axis and is convex at its circumference. The second lens L 2  has a negative refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is concave at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a positive refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is convex at the optical axis and is concave at its circumference, and the image side surface S 9  is concave at the optical axis and is concave at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 12 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 5, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 13 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 5, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 14 shows values of relevant parameters of the lens system  10  given in Embodiment 5. 
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Embodiment 5 
               
               
                 f = 40 mm, FNO = 4.9, HFOV = 3.26°, TTL = 19.00 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface 
                 Radius of 
                   
                   
                 Refractive 
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 Thickness  
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
               
                 OBJ 
                 Object plane 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −4.650 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 4.650 
                 4.650 
               
               
                 S2 
                 angle prism 
                 Spherical 
                 Infinite 
                 4.650 
                   
                   
                   
                   
                 Reflection 
                 4.650 
                 6.576 
               
               
                 S3 
                   
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 4.650 
                 4.650 
               
               
                 STO 
                 Optical stop  
                 Spherical 
                 Infinite 
                 0.100 
                   
                   
                   
                   
                 Refraction 
                 4.082 
                 4.082 
               
               
                 S4 
                 First lens 
                 Aspherical 
                 5.580 
                 3.700 
                 Plastic  
                 1.546 
                 56.114 
                 −999.999 
                 Refraction 
                 4.187 
                 4.187 
               
               
                 S5 
                   
                 Aspherical 
                 4.230 
                 0.390 
                   
                   
                   
                   
                 Refraction 
                 3.356 
                 3.356 
               
               
                 S6 
                 Second lens 
                 Aspherical 
                 4.981 
                 1.400 
                 Plastic  
                 1.644 
                 23.517 
                 −921.028 
                 Refraction 
                 3.274 
                 3.274 
               
               
                 S7 
                   
                 Aspherical 
                 3.241 
                 0.527 
                   
                   
                   
                   
                 Refraction 
                 2.890 
                 2.890 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 3.232 
                 3.800 
                 Plastic  
                 1.546 
                 56.114 
                 9.637 
                 Refraction 
                 2.874 
                 2.874 
               
               
                 S9 
                   
                 Aspherical 
                 4.903 
                 1.321 
                   
                   
                   
                   
                 Refraction 
                 2.403 
                 2.403 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518  
                 64.166 
                   
                 Refraction 
                 2.398 
                 2.398 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.590 
                   
                   
                   
                   
                 Refraction 
                 2.397 
                 2.397 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.900 
                 Glass 
                 1.518  
                 64.166 
                   
                 Refraction 
                 2.900 
                 2.900 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −2.900 
                   
                   
                   
                   
                 Reflection 
                 4.101 
                 2.900 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −1.812 
                   
                   
                   
                   
                 Refraction 
                 2.900 
                 2.900 
               
               
                 S15 
                 Third right- 
                 Spherical 
                 Infinite 
                 −2.700 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.700 
                 2.700 
               
               
                 S16 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.700 
                   
                   
                   
                   
                 Reflection 
                 3.818 
                 2.700 
               
               
                 S17 
                   
                 Spherical 
                 Infinite 
                 8.872 
                   
                   
                   
                   
                 Refraction 
                 2.700 
                 2.700 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 Embodiment 5 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A4 
                 4.0000E−04 
                   4.6100E−03 
                   6.7000E−04 
                 −4.7700E−03 
                 −1.7000E−04 
                 6.6000E−04 
               
               
                 A6 
                 2.0000E−05 
                   7.8000E−04 
                   1.0900E−03 
                   2.2900E−03 
                   1.5400E−03 
                 3.7000E−04 
               
               
                 A8 
                 0.0000E+00 
                 −1.4000E−04 
                 −1.5000E−04 
                 −2.0000E−04 
                 −1.1000E−04 
                 2.0000E−05 
               
               
                 A10 
                 0.0000E+00 
                   1.0000E−05 
                   1.0000E−05 
                   1.0000E−05 
                   1.0000E−05 
                 0.0000E+00 
               
               
                 A12 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A14 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A16 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A18 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                 A20 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 14 
               
               
                   
               
               
                 Embodiment 5 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 40 
                 f/FNO (mm) 
                 8.163 
               
               
                 FNO 
                 4.9 
                 HFOV/TTL (degrees/mm) 
                 0.172 
               
               
                 HFOV (degrees) 
                 3.26 
                 TTL/f 
                 0.475 
               
               
                 TTL 
                 19.0 
                 CT12/CT23 
                 0.739 
               
               
                 ImgH 
                 2.285 
                 D32/ImgH 
                 1.052 
               
               
                   
               
            
           
         
       
     
       FIG. 20  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 5, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 20 , it can be seen that the lens system  10  provided in Embodiment 5 can achieve good imaging quality. 
     Embodiment 6 
     A lens system  10  of Embodiment 6 of the present disclosure will be described below with reference to  FIGS. 21 to 24 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 21 to 23 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a positive refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is convex at the optical axis and is convex at its circumference. The second lens L 2  has a positive refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is concave at its circumference, and the image side surface S 7  is convex at the optical axis and is convex at its circumference. The third lens L 3  has a negative refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is convex at the optical axis and is convex at its circumference, and the image side surface S 9  is concave at the optical axis and is concave at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 15 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 6, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 16 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 6, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 17 shows values of relevant parameters of the lens system  10  given in Embodiment 6. 
     
       
         
           
               
             
               
                 TABLE 15 
               
             
            
               
                   
               
               
                 Embodiment 6 
               
               
                 f = 25.13 mm, FNO = 4.9, HFOV = 5.16°, TTL = 18.01 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface 
                 Radius of 
                   
                   
                 Refractive 
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 Thickness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
               
                 OBJ 
                 Object plane 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −2.750 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.750 
                 2.750 
               
               
                 S2 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.750 
                   
                   
                   
                   
                 Reflection 
                 2.750 
                 3.889 
               
               
                 S3 
                   
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 2.750 
                 2.750 
               
               
                 STO 
                 Optical stop  
                 Spherical 
                 Infinite 
                 0.100 
                   
                   
                   
                   
                 Refraction 
                 2.564 
                 2.564 
               
               
                 S4 
                 First lens 
                 Aspherical 
                 37.934 
                 2.100 
                 Plastic 
                 1.546 
                 56.114 
                 52.000 
                 Refraction 
                 2.590 
                 2.590 
               
               
                 S5 
                   
                 Aspherical 
                 −110.612 
                 0.760 
                   
                   
                   
                   
                 Refraction 
                 2.547 
                 2.547 
               
               
                 S6 
                 Second lens 
                 Aspherical 
                 57.291 
                 1.950 
                 Plastic 
                 1.644 
                 23.517 
                 52.754 
                 Refraction 
                 2.439 
                 2.439 
               
               
                 S7 
                   
                 Aspherical 
                 −82.366 
                 0.717 
                   
                   
                   
                   
                 Refraction 
                 2.914 
                 2.914 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 17.272 
                 3.900 
                 Plastic 
                 1.546 
                 56.114 
                 1000.212 
                 Refraction 
                 2.984 
                 2.984 
               
               
                 S9 
                   
                 Aspherical 
                 15.408 
                 1.709 
                   
                   
                   
                   
                 Refraction 
                 2.377 
                 2.377 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.370 
                 2.370 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.788 
                   
                   
                   
                   
                 Refraction 
                 2.369 
                 2.369 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.600 
                   
                   
                   
                   
                 Refraction 
                 2.600 
                 2.600 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −2.600 
                 Glass 
                 1.518 
                 64.166 
                   
                 Reflection 
                 3.677 
                 2.600 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −1.575 
                   
                   
                   
                   
                 Refraction 
                 2.600 
                 2.600 
               
               
                 S15 
                 Third right-  
                 Spherical 
                 Infinite 
                 −2.600 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.600 
                 2.600 
               
               
                 S16 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.600 
                   
                   
                   
                   
                 Reflection 
                 3.677 
                 2.600 
               
               
                 S17 
                   
                 Spherical 
                 Infinite 
                 7.451 
                   
                   
                   
                   
                 Refraction 
                 2.600 
                 2.600 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 16 
               
             
            
               
                   
               
               
                 Embodiment 6 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                 −2.1500E−03 
                   8.5600E−03 
                   1.9110E−02 
                   1.8600E−03 
                 −1.5240E−02 
                 −7.3700E−03 
               
               
                 A6 
                   1.2000E−04 
                 −1.8000E−04 
                   7.9000E−04 
                   1.1400E−03 
                   2.0700E−03 
                   6.0000E−05 
               
               
                 A8 
                 −3.0000E−05 
                 −8.0000E−05 
                 −1.9000E−04 
                 −1.3000E−04 
                 −1.7000E−04 
                 −2.0000E−05 
               
               
                 A10 
                   0.0000E+00 
                   1.0000E−05 
                   1.0000E−05 
                   0.0000E+00 
                   1.0000E−05 
                   0.0000E+00 
               
               
                 A12 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A18 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 17 
               
               
                   
               
               
                 Embodiment 6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 25.13 
                 f/FNO (mm) 
                 5.128 
               
               
                 ENO 
                 4.9 
                 HFOV/TTL (degrees/mm) 
                 0.287 
               
               
                 HFOV (degrees) 
                 5.16 
                 TTL/f 
                 0.717 
               
               
                 TTL 
                 18.01 
                 CT12/CT23 
                 1.06 
               
               
                 ImgH 
                 2.285 
                 D32/ImgH 
                 1.04 
               
               
                   
               
            
           
         
       
     
       FIG. 24  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 6, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 24 , it can be seen that the lens system  10  provided in Embodiment 6 can achieve good imaging quality. 
     Embodiment 7 
     A lens system  10  of Embodiment 7 of the present disclosure will be described below with reference to  FIGS. 25 to 28 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 25 to 27 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a negative refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is concave at the optical axis and is concave at its circumference. The second lens L 2  has a positive refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is concave at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a positive refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is convex at the optical axis and is convex at its circumference, and the image side surface S 9  is concave at the optical axis and is concave at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 18 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 7, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 19 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 7, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 20 shows values of relevant parameters of the lens system  10  given in Embodiment 7. 
     
       
         
           
               
             
               
                 TABLE 18 
               
             
            
               
                   
               
               
                 Embodiment 7 
               
               
                 f = 27 mm, FNO = 5.87, HFOV = 4.81°, TTL = 19.71 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface  
                 Radius of 
                   
                   
                 Refractive  
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 Thickness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
               
                 OBJ 
                 Object plane 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −2.500 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S2 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.500 
                   
                   
                   
                   
                 Reflection 
                 2.500 
                 3.536 
               
               
                 S3 
                   
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 STO 
                 Optical stop 
                 Spherical 
                 Infinite 
                 0.100 
                   
                   
                   
                   
                 Refraction 
                 2.300 
                 2.300 
               
               
                 S4 
                 First lens 
                 Aspherical 
                 12.521 
                 3.635 
                 Plastic  
                 1.546 
                 56.114 
                 −22897.674 
                 Refraction 
                 2.327 
                 2.327 
               
               
                 S5 
                   
                 Aspherical 
                 11.226 
                 1.650 
                   
                   
                   
                   
                 Refraction 
                 2.270 
                 2.270 
               
               
                 S6 
                 Second lens 
                 Aspherical 
                 11.318 
                 1.664 
                 Plastic 
                 1.644 
                 23.517 
                 1000.038 
                 Refraction 
                 2.290 
                 2.290 
               
               
                 S7 
                   
                 Aspherical 
                 10.857 
                 0.559 
                   
                   
                   
                   
                 Refraction 
                 2.513 
                 2.513 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 6.896 
                 3.800 
                 Plastic 
                 1.546 
                 56.114 
                 23.425 
                 Refraction 
                 2.614 
                 2.614 
               
               
                 S9 
                   
                 Aspherical 
                 12.055 
                 1.529 
                   
                   
                   
                   
                 Refraction 
                 2.154 
                 2.154 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.163 
                 2.163 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.919 
                   
                   
                   
                   
                 Refraction 
                 2.164 
                 2.164 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.400 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.400 
                 2.400 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −2.400 
                   
                   
                   
                   
                 Reflection 
                 3.394 
                 2.400 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −1.740 
                   
                   
                   
                   
                 Refraction 
                 2.400 
                 2.400 
               
               
                 S15 
                 Third right- 
                 Spherical 
                 Infinite 
                 −2.550 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.550 
                 2.550 
               
               
                 S16 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.550 
                   
                   
                   
                   
                 Reflection 
                 3.606 
                 2.550 
               
               
                 S17 
                   
                 Spherical 
                 Infinite 
                 7.483 
                   
                   
                   
                   
                 Refraction 
                 2.550 
                 2.550 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 19 
               
             
            
               
                   
               
               
                 Embodiment 7 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                   5.9000E−04 
                   9.4200E−03 
                   1.8640E−02 
                   5.6100E−03 
                 −1.3360E−02 
                 −7.2900E−03 
               
               
                 A6 
                 −1.1000E−04 
                 −1.1600E−03 
                 −1.4000E−04 
                   1.2100E−03 
                   2.6200E−03 
                 −1.0000E−05 
               
               
                 A8 
                   0.0000E+00 
                   9.0000E−05 
                 −1.8000E−04 
                 −2.1000E−04 
                 −2.6000E−04 
                   5.0000E−05 
               
               
                 A10 
                   0.0000E+00 
                 −1.0000E−05 
                   1.0000E−05 
                   1.0000E−05 
                   1.0000E−05 
                   0.0000E+00 
               
               
                 A12 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A18 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 20 
               
               
                   
               
               
                 Embodiment 7 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 27 
                 f/FNO (mm) 
                 4.6 
               
               
                 FNO 
                 5.87 
                 HFOV/TTL (degrees/mm) 
                 0.244 
               
               
                 HFOV (degrees) 
                 4.81 
                 TTL/f 
                 0.73 
               
               
                 TTL 
                 19.71 
                 CT12/CT23 
                 2.953 
               
               
                 ImgH 
                 2.285 
                 D32/ImgH 
                 0.943 
               
               
                   
               
            
           
         
       
     
       FIG. 28  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 7, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 28 , it can be seen that the lens system  10  provided in Embodiment 7 can achieve good imaging quality. 
     Embodiment 8 
     A lens system  10  of Embodiment 8 of the present disclosure will be described below with reference to  FIGS. 29 to 32 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 29 to 31 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a positive refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is concave at the optical axis and is convex at its circumference. The second lens L 2  has a negative refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is concave at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a positive refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is convex at the optical axis and is concave at its circumference, and the image side surface S 9  is concave at the optical axis and is convex at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 21 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 8, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 22 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 8, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 23 shows values of relevant parameters of the lens system  10  given in Embodiment 8. 
     
       
         
           
               
             
               
                 TABLE 21 
               
             
            
               
                   
               
               
                 Embodiment 8 
               
               
                 f = 27.14 mm, FNO = 2.5, HFOV = 4.81°, TTL = 16.09 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface  
                 Radius of 
                   
                   
                 Refractive  
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 Thickness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
               
                 OBJ 
                 Object plane  
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −6.500 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 6.500 
                 6.500 
               
               
                 S2 
                 angle prism 
                 Spherical 
                 Infinite 
                 6.500 
                   
                   
                   
                   
                 Reflection 
                 6.500 
                 9.192 
               
               
                 S3 
                   
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 6.500 
                 6.500 
               
               
                 STO 
                 Optical stop  
                 Spherical 
                 Infinite 
                 −0.411 
                   
                   
                   
                   
                 Refraction 
                 5.412 
                 5.412 
               
               
                 S4 
                 First lens 
                 Aspherical 
                 9.035 
                 3.201 
                 Plastic  
                 1.546 
                 56.114 
                 49.507 
                 Refraction 
                 5.495 
                 5.495 
               
               
                 S5 
                   
                 Aspherical 
                 11.874 
                 0.359 
                   
                   
                   
                   
                 Refraction 
                 5.225 
                 5.225 
               
               
                 S6 
                 Second lens 
                 Aspherical 
                 11.354 
                 1.451 
                 Plastic  
                 1.644 
                 23.517 
                 −21.847 
                 Refraction 
                 5.162 
                 5.162 
               
               
                 S7 
                   
                 Aspherical 
                 5.969 
                 1.747 
                   
                   
                   
                   
                 Refraction 
                 5.153 
                 5.153 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 5.406 
                 2.731 
                 Plastic 
                 1.546 
                 56.114 
                 15.017 
                 Refraction 
                 4.713 
                 4.713 
               
               
                 S9 
                   
                 Aspherical 
                 13.039 
                 1.130 
                   
                   
                   
                   
                 Refraction 
                 4.440 
                 4.440 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 4.407 
                 4.407 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.202 
                   
                   
                   
                   
                 Refraction 
                 4.391 
                 4.391 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 4.400 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 4.400 
                 4.400 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −4.400 
                   
                   
                   
                   
                 Reflection 
                 6.223 
                 4.400 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −1.132 
                   
                   
                   
                   
                 Refraction 
                 4.400 
                 4.400 
               
               
                 S15 
                 Third right- 
                 Spherical 
                 Infinite 
                 −3.750 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 3.750 
                 3.750 
               
               
                 S16 
                 angle prism 
                 Spherical 
                 Infinite 
                 3.750 
                   
                   
                   
                   
                 Reflection 
                 5.303 
                 3.750 
               
               
                 S17 
                   
                 Spherical 
                 Infinite 
                 6.187 
                   
                   
                   
                   
                 Refraction 
                 3.750 
                 3.750 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.287 
                 2.287 
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 22 
               
             
            
               
                   
               
               
                 Embodiment 8 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                   2.4000E−04 
                 −1.7000E−04 
                   3.0000E−05 
                 1.7000E−03 
                 6.0000E−04 
                 −1.2600E−03 
               
               
                 A6 
                   0.0000E+00 
                   1.0000E−04 
                   1.2000E−04 
                 1.0000E−04 
                 3.0000E−05 
                 −1.0000E−05 
               
               
                 A8 
                   0.0000E+00 
                   0.0000E+00 
                 −1.0000E−05 
                 0.0000E+00 
                 0.0000E+00 
                   1.0000E−05 
               
               
                 A10 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
                   0.0000E+00 
               
               
                 A12 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
                   0.0000E+00 
               
               
                 A18 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 23 
               
               
                   
               
               
                 Embodiment 8 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 27.14 
                 f/FNO (mm) 
                 10.855 
               
               
                 FNO 
                 2.5 
                 HFOV/TTL (degrees/mm) 
                 0.299 
               
               
                 HFOV (degrees) 
                 4.81 
                 TTL/f 
                 0.593 
               
               
                 TTL 
                 16.09 
                 CT12/CT23 
                 0.206 
               
               
                 ImgH 
                 2.287 
                 D32/ImgH 
                 1.067 
               
               
                   
               
            
           
         
       
     
       FIG. 32  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 8, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 32 , it can be seen that the lens system  10  provided in Embodiment 8 can achieve good imaging quality. 
     Embodiment 9 
     A lens system  10  of Embodiment 9 of the present disclosure will be described below with reference to  FIGS. 33 to 36 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 31 to 35 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a positive refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is convex at the optical axis and is convex at its circumference. The second lens L 2  has a negative refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is concave at the optical axis and is concave at its circumference, and the image side surface S 7  is convex at the optical axis and is convex at its circumference. The third lens L 3  has a negative refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is convex at the optical axis and is concave at its circumference, and the image side surface S 9  is concave at the optical axis and is concave at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 24 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 9, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 25 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 9, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 26 shows values of relevant parameters of the lens system  10  given in Embodiment 9. 
     
       
         
           
               
             
               
                 TABLE 24 
               
             
            
               
                   
               
               
                 Embodiment 9 
               
               
                 f = 25.76 mm, FNO = 3.3, HFOV = 5.03°, TTL = 17.54 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface  
                 Radius of 
                   
                   
                 Refractive  
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 Thickness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
               
                 OBJ 
                 Object 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −4.550 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 4.550 
                 4.550 
               
               
                 S2 
                 angle 
                 Spherical 
                 Infinite 
                 4.550 
                   
                   
                   
                   
                 Reflection 
                 4.550 
                 6.435 
               
               
                 S3 
                 prism 
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 4.550 
                 4.550 
               
               
                 STO 
                 Optical 
                 Spherical 
                 Infinite 
                 −0.225 
                   
                   
                   
                   
                 Refraction 
                 3.903 
                 3.903 
               
               
                   
                 stop 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S4 
                 First  
                 Aspherical 
                 12.772 
                 3.184 
                 Plastic  
                 1.546 
                 56.114 
                 15.716 
                 Refraction 
                 3.937 
                 3.937 
               
               
                 S5 
                 lens 
                 Aspherical 
                 −23.836 
                 0.183 
                   
                   
                   
                   
                 Refraction 
                 3.767 
                 3.767 
               
               
                 S6 
                 Second 
                 Aspherical 
                 −11.814 
                 1.350 
                 Plastic  
                 1.644 
                 23.517 
                 −31.524 
                 Refraction 
                 3.710 
                 3.710 
               
               
                 S7 
                 lens 
                 Aspherical 
                 −29.521 
                 2.841 
                   
                   
                   
                   
                 Refraction 
                 3.804 
                 3.804 
               
               
                 S8 
                 Third  
                 Aspherical 
                 7.141 
                 2.653 
                 Plastic 
                 1.546 
                 56.114 
                 −075.779 
                 Refraction 
                 3.647 
                 3.647 
               
               
                 S9 
                 lens 
                 Aspherical 
                 6.177 
                 1.435 
                   
                   
                   
                   
                 Refraction 
                 2.946 
                 2.946 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.930 
                 2.930 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 3.557 
                   
                   
                   
                   
                 Refraction 
                 2.924 
                 2.924 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.950 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.950 
                 2.950 
               
               
                 S13 
                 right-angle  
                 Spherical 
                 Infinite 
                 −2.950 
                   
                   
                   
                   
                 Reflection 
                 4.172 
                 2.950 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −0.746 
                   
                   
                   
                   
                 Refraction 
                 2.950 
                 2.950 
               
               
                 S15 
                 Third 
                 Spherical 
                 Infinite 
                 −2.750 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.750 
                 2.750 
               
               
                 S16 
                 right-angle  
                 Spherical 
                 Infinite 
                 2.750 
                   
                   
                   
                   
                 Reflection 
                 3.889 
                 2.750 
               
               
                 S17 
                 prism 
                 Spherical 
                 Infinite 
                 2.870 
                   
                   
                   
                   
                 Refraction 
                 2.750 
                 2.750 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.290 
                 2.290 
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 25 
               
             
            
               
                   
               
               
                 Embodiment 9 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                 3.5000E−04 
                 −1.1000E−03 
                 −6.6100E−03 
                 −6.8800E−03 
                 −4.4700E−03 
                 −4.1100E−03 
               
               
                 A6 
                 1.0000E−05 
                   3.6000E−04 
                   7.4000E−04 
                   3.7000E−04 
                   1.6000E−04 
                 −1.1000E−04 
               
               
                 A8 
                 0.0000E+00 
                 −5.0000E−05 
                 −6.0000E−05 
                   0.0000E+00 
                 −1.0000E−05 
                   0.0000E+00 
               
               
                 A10 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A12 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A18 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 26 
               
               
                   
               
               
                 Embodiment 9 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 25.76 
                 f/FNO (mm) 
                 7.806 
               
               
                 FNO 
                 3.3 
                 HFOV/TTL (degrees/mm) 
                 0.287 
               
               
                 HFOV (degrees) 
                 5.03 
                 TTL/f 
                 0.681 
               
               
                 TTL 
                 17.54 
                 CT12/CT23 
                 0.064 
               
               
                 ImgH 
                 2.290 
                 D32/ImgH 
                 1.287 
               
               
                   
               
            
           
         
       
     
       FIG. 36  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 9, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 36 , it can be seen that the lens system  10  provided in Embodiment 9 can achieve good imaging quality. 
     Embodiment 10 
     A lens system  10  of Embodiment 10 of the present disclosure will be described below with reference to  FIGS. 37 to 40 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 37 to 39 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a positive refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is concave at the optical axis and is convex at its circumference. The second lens L 2  has a negative refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is concave at the optical axis and is concave at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a positive refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is convex at the optical axis and is convex at its circumference, and the image side surface S 9  is concave at the optical axis and is concave at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 27 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 10, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 28 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 10, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 29 shows values of relevant parameters of the lens system  10  given in Embodiment 10. 
     
       
         
           
               
             
               
                 TABLE 27 
               
             
            
               
                   
               
               
                 Embodiment 10 
               
               
                 f = 27.4 mm, FNO = 4.1, HFOV = 4.74°, TTL = 18.02 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface  
                 Radius of 
                   
                   
                 Refractive  
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 Thickness 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
               
                 OBJ 
                 Object plane 
                 Spherical 
                 Infinite 
                 Infinite 
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −3.900 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 3.900 
                 3.900 
               
               
                 S2 
                 angle prism 
                 Spherical 
                 Infinite 
                 3.900 
                   
                   
                   
                   
                 Reflection 
                 3.900 
                 5.515 
               
               
                 S3 
                   
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 3.900 
                 3.900 
               
               
                 STO 
                 Optical stop  
                 Spherical 
                 Infinite 
                 0.100 
                   
                   
                   
                   
                 Refraction 
                 3.342 
                 3.342 
               
               
                 S4 
                 First lens 
                 Aspherical 
                 11.057 
                 2.532 
                 Plastic  
                 1.546 
                 56.114 
                 22.212 
                 Refraction 
                 3.390 
                 3.390 
               
               
                 S5 
                   
                 Aspherical 
                 115.264 
                 0.243 
                   
                   
                   
                   
                 Refraction 
                 3.272 
                 3.272 
               
               
                 S6 
                 Second lens 
                 Aspherical 
                 −21.810 
                 1.550 
                 Plastic  
                 1.644 
                 23.517 
                 −29.421 
                 Refraction 
                 3.254 
                 3.254 
               
               
                 S7 
                   
                 Aspherical 
                 148.398 
                 2.651 
                   
                   
                   
                   
                 Refraction 
                 3.257 
                 3.257 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 6.033 
                 3.900 
                 Plastic  
                 1.546 
                 56.114 
                 45.000 
                 Refraction 
                 3.356 
                 3.356 
               
               
                 S9 
                   
                 Aspherical 
                 6.171 
                 1.261 
                   
                   
                   
                   
                   
                   
                   
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.602 
                 2.602 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.722 
                   
                   
                   
                   
                 Refraction 
                 2.599 
                 2.599 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.700 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.700 
                 2.700 
               
               
                 S13 
                 right-angle 
                 Spherical 
                 Infinite 
                 −2.700 
                   
                   
                   
                   
                 Reflection 
                 3.818 
                 2.700 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −1.476 
                   
                   
                   
                   
                 Refraction 
                 2.700 
                 2.700 
               
               
                 S15 
                 Third right- 
                 Spherical 
                 Infinite 
                 −2.650 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.650 
                 2.650 
               
               
                 S16 
                 angle prism 
                 Spherical 
                 Infinite 
                 2.650 
                   
                   
                   
                   
                 Reflection 
                 3.748 
                 2.650 
               
               
                 S17 
                   
                 Spherical 
                 Infinite 
                 6.424 
                   
                   
                   
                   
                 Refraction 
                 2.650 
                 2.650 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 28 
               
             
            
               
                   
               
               
                 Embodiment 10 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                 6.9000E−04 
                 −1.3000E−04 
                 −6.3200E−03 
                 −7.2800E−03 
                 −2.7700E−03 
                 −2.7600E−03 
               
               
                 A6 
                 1.0000E−05 
                   2.9000E−04 
                   7.2000E−04 
                   4.5000E−04 
                   1.8000E−04 
                 −5.0000E−05 
               
               
                 A8 
                 0.0000E+00 
                 −5.0000E−05 
                 −6.0000E−05 
                   1.0000E−05 
                 −1.0000E−05 
                   1.0000E−05 
               
               
                 A10 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A12 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A18 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                 0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 29 
               
               
                   
               
               
                 Embodiment 10 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 27.4 
                 f/FNO (mm) 
                 6.684 
               
               
                 FNO 
                 4.1 
                 HFOV/TTL (degrees/mm) 
                 0.263 
               
               
                 HFOV (degrees) 
                 4.74 
                 TTL/f 
                 0.657 
               
               
                 TTL 
                 18.02 
                 CT12/CT23 
                 0.092 
               
               
                 ImgH 
                 2.285 
                 D32/ImgH 
                 1.144 
               
               
                   
               
            
           
         
       
     
       FIG. 40  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 10, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 40 , it can be seen that the lens system  10  provided in Embodiment 10 can achieve good imaging quality. 
     Embodiment 11 
     A lens system  10  of Embodiment 11 of the present disclosure will be described below with reference to  FIGS. 41 to 44 . In this embodiment, for the sake of brevity, some descriptions similar to those in Embodiment 1 will be omitted. 
     As shown in  FIGS. 41 to 43 , the lens system  10  includes, sequentially arranged from an object side to an image side along an optical axis, a first right-angle prism P 1 , a first lens L 1 , a second lens L 2 , a third lens L 3 , a second right-angle prism P 2 , a third right-angle prism P 3 , and an imaging plane S 18 . The folded optical axis includes a first part AX 1 , a second part AX 2 , a third part AX 3 , and a fourth part AX 4 . The first lens L 1 , the second lens L 2 , and the third lens L 3  are located on the optical axis AX 2 . 
     The first right-angle prism P 1  has a light incident surface S 1 , a reflective surface S 2 , and a light emergent surface S 3 . 
     The first lens L 1  has a positive refractive power, and an object side surface S 4  and an image side surface S 5  thereof are both aspherical. The object side surface S 4  is convex at the optical axis and is convex at its circumference, and the image side surface S 5  is concave at the optical axis and is concave at its circumference. The second lens L 2  has a negative refractive power, and an object side surface S 6  and an image side surface S 7  thereof are both aspherical. The object side surface S 6  is convex at the optical axis and is concave at its circumference, and the image side surface S 7  is concave at the optical axis and is convex at its circumference. The third lens L 3  has a positive refractive power, and an object side surface S 8  and an image side surface S 9  thereof are both aspherical. The object side surface S 8  is concave at the optical axis and is concave at its circumference, and the image side surface S 9  is convex at the optical axis and is convex at its circumference. 
     The second right-angle prism P 2  has a light incident surface S 12 , a reflective surface S 13 , and a light emergent surface S 14 . 
     The third right-angle prism P 3  has a light incident surface S 15 , a reflective surface S 16 , and a light emergent surface S 17 . 
     The object side surfaces and the image side surfaces of the first lens L 1  to the third lens L 3  are all configured to be aspherical. The first lens L 1  to the third lens L 3  are all made of plastic. An optical stop STO is further disposed between the first right-angle prism P 1  and the first lens L 1 . The lens system  10  further includes an infrared filter  110  disposed on an image side of the third lens L 3  and having an object side surface S 10  and an image side surface S 11 . 
     Table 30 shows the surface type, radius of curvature, thickness, material, refractive index, Abbe number (that is, dispersion coefficient), effective focal length, Y-half aperture, and X-half aperture of each of the lenses of the lens system  10  according to Embodiment 11, where the units of the radius of curvature, the thickness, the effective focal length of each of the lenses, the Y-half aperture, and the X-half aperture are all millimeters (mm) Table 31 shows the high-order term coefficients that can be used for the lens aspherical surfaces S 4  to S 9  in Embodiment 11, where the surface shape of the aspherical surface can be defined by the equation (1) provided in Embodiment 1. Table 32 shows values of relevant parameters of the lens system  10  given in Embodiment 11. 
     
       
         
           
               
             
               
                 TABLE 30 
               
             
            
               
                   
               
               
                 Embodiment 11 
               
               
                 f = 25.3 mm, FNO = 4.9, HFOV = 5.16°, TTL = 17.64 mm 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 Surface 
                 Surface  
                 Radius of 
                   
                   
                 Refractive  
                 Abbe 
                 Focal 
                 Refraction 
                 Y-half 
                 X-half 
               
               
                 number 
                 name 
                 type 
                 curvature 
                 Infinite 
                 Material 
                 index 
                 number 
                 length 
                 mode 
                 aperture 
                 aperture 
               
               
                   
               
               
                 OBJ 
                 Object 
                 Spherical 
                 Infinite 
                   
                   
                   
                   
                   
                 Refraction 
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S1 
                 First right- 
                 Spherical 
                 Infinite 
                 −3.500 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 3.500 
                 3.500 
               
               
                 S2 
                 angle 
                 Spherical 
                 Infinite 
                 3.500 
                   
                   
                   
                   
                 Reflection 
                 3.500 
                 4.950 
               
               
                 S3 
                 prism 
                 Spherical 
                 Infinite 
                 0.700 
                   
                   
                   
                   
                 Refraction 
                 3.500 
                 3.500 
               
               
                 STO 
                 Optical 
                 Spherical 
                 Infinite 
                 −0.348 
                   
                   
                   
                   
                 Refraction 
                 2.582 
                 2.582 
               
               
                   
                 stop 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 S4 
                 First lens 
                 Aspherical 
                 10.935 
                 2.582 
                 Plastic 
                 1.546 
                 56.114 
                 23.851 
                 Refraction 
                 2.582 
                 2.582 
               
               
                 S5 
                   
                 Aspherical 
                 62.580 
                 0.158 
                   
                   
                   
                   
                 Refraction 
                 2.450 
                 2.450 
               
               
                 S6 
                 Second 
                 Aspherical 
                 5.690 
                 1.400 
                 Plastic 
                 1.644 
                 23.517 
                 −14.877 
                 Refraction 
                 2.480 
                 2.480 
               
               
                 S7 
                 lens 
                 Aspherical 
                 3.226 
                 1.731 
                   
                   
                   
                   
                 Refraction 
                 2.322 
                 2.322 
               
               
                 S8 
                 Third lens 
                 Aspherical 
                 −24.107 
                 2.180 
                 Plastic 
                 1.546 
                 56.114 
                 16.076 
                 Refraction 
                 2.491 
                 2.491 
               
               
                 S9 
                   
                 Aspherical 
                 −6.640 
                 1.715 
                   
                   
                   
                   
                 Refraction 
                 2.770 
                 2.770 
               
               
                 S10 
                 Infrared 
                 Spherical 
                 Infinite 
                 0.210 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.717 
                 2.717 
               
               
                 S11 
                 filter 
                 Spherical 
                 Infinite 
                 0.853 
                   
                   
                   
                   
                 Refraction 
                 2.714 
                 2.714 
               
               
                 S12 
                 Second 
                 Spherical 
                 Infinite 
                 2.500 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S13 
                 right-angle  
                 Spherical 
                 Infinite 
                 −2.500 
                   
                   
                   
                   
                 Reflection 
                 3.536 
                 2.500 
               
               
                 S14 
                 prism 
                 Spherical 
                 Infinite 
                 −2.707 
                   
                   
                   
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S15 
                 Third 
                 Spherical 
                 Infinite 
                 −2.500 
                 Glass 
                 1.518 
                 64.166 
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S16 
                 right-angle  
                 Spherical 
                 Infinite 
                 2.500 
                   
                   
                   
                   
                 Reflection 
                 3.536 
                 2.500 
               
               
                 S17 
                 prism 
                 Spherical 
                 Infinite 
                 9.515 
                   
                   
                   
                   
                 Refraction 
                 2.500 
                 2.500 
               
               
                 S18 
                 Imaging 
                 Spherical 
                 Infinite 
                 0.000 
                   
                   
                   
                   
                 Refraction 
                 2.285 
                 2.285 
               
               
                   
                 plane 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 31 
               
             
            
               
                   
               
               
                 Embodiment 11 
               
               
                 Aspheric coefficient 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Surface 
                   
                   
                   
                   
                   
                   
               
               
                 number 
                 S4 
                 S5 
                 S6 
                 S7 
                 S8 
                 S9 
               
               
                   
               
               
                 K 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A4 
                 −7.4000E−04 
                 −4.7400E−03 
                 −5.3000E−04 
                   4.0600E−03 
                 −1.9800E−03 
                 −7.0000E−05 
               
               
                 A6 
                 −5.0000E−05 
                   6.3000E−04 
                   1.0900E−03 
                   1.4700E−03 
                   3.6000E−04 
                   8.0000E−05 
               
               
                 A8 
                   0.0000E+00 
                 −1.5000E−04 
                 −2.0000E−04 
                 −2.2000E−04 
                 −1.0000E−05 
                   0.0000E+00 
               
               
                 A10 
                   0.0000E+00 
                   1.0000E−05 
                   1.0000E−05 
                   2.0000E−05 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A12 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A14 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A16 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A18 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                 A20 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
                   0.0000E+00 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 32 
               
               
                   
               
               
                 Embodiment 11 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 f (mm) 
                 25.3 
                 f/FNO (mm) 
                 5.163 
               
               
                 FNO 
                 4.9 
                 HFOV/TTL (degrees/mm) 
                 0.293 
               
               
                 HFOV (degrees) 
                 5.16 
                 TTL/f 
                 0.697 
               
               
                 TTL 
                 17.64 
                 CT12/CT23 
                 0.091 
               
               
                 ImgH 
                 2.285 
                 D32/ImgH 
                 1.212 
               
               
                   
               
            
           
         
       
     
       FIG. 44  shows graphs of longitudinal spherical aberration, astigmatism, and distortion of the lens system  10  according to Embodiment 11, respectively. The reference wavelength of the lens system  10  is 555 nm. The graph of longitudinal spherical aberration shows the deviation of the convergent focus of light rays with wavelengths of 470 nm, 510 nm, 555 nm, 610 nm, and 650 nm after passing through the lens system  10 . The graph of astigmatism shows the curvature of meridian image plane and the curvature of sagittal image plane of the lens system  10 . The graph of distortion shows the distortion of the lens system  10  with different image heights. According to  FIG. 44 , it can be seen that the lens system  10  provided in Embodiment 11 can achieve good imaging quality. 
     As shown in  FIG. 45 , the present disclosure further provides an imaging module  20 , which includes the lens system  10  as described above and a photosensitive element  210 . The photosensitive element  210  is disposed on the image side of the lens system  10 . A photosensitive surface of the photosensitive element  210  coincides with the imaging plane S 18 . Specifically, the photosensitive element  210  may adopt a complementary metal oxide semiconductor (CMOS) image sensor or a charge-coupled device (CCD) image sensor. 
     The above imaging module  20  can be arranged in a transverse direction of the electronic product, so as to be conveniently adapted to devices with limited size, such as thin and light electronic equipment. In addition, the imaging module  20  further has a long focal length, which can clearly image the distant objects, thereby better meeting the needs of long-distance shooting of mobile phones and tablets. 
     In some other embodiments, each optical element and the photosensitive element  210  in the imaging module  20  may also be respectively provided with a driving element to drive the corresponding optical element and the photosensitive element  210  to focus the light rays onto the imaging plane, thereby achieving at least one of the zoom, focusing, or anti-shake functions of the imaging module  20 . 
     The present disclosure further provides an electronic device, which includes a housing and the imaging module  20  as described above, and the imaging module  20  is mounted on the housing. Specifically, the imaging module  20  is disposed inside the housing and exposed from the housing to acquire images. The housing can provide protections of dustproof, waterproof, and drop resistance for the imaging module  20 . The housing is provided with an opening corresponding to the imaging module  20  to allow light rays to penetrate into or out of the housing through the opening. 
     The above described electronic device has the characteristics of light and thin structure, and also has a strong telephoto capability, which can improve the shooting experience of a user. 
     In some other embodiments, the “electronic device” used may further include, but is not limited to, a device configured to be connected via a wired line and/or to receive or send a communication signal via a wireless interface. An electronic device configured to communicate through a wireless interface may be referred to as a “wireless communication terminal”, a “wireless terminal”, or a “mobile terminal”. Examples of the mobile terminal include, but are not limited to a satellite or cellular phone; a personal communication system (PCS) terminal that can combine a cellular radio phone with data processing, fax, and data communication capabilities; a personal digital assistant (PDA) that can include a radio phone, a pager, an Internet/Intranet access, a Web browser, a memo pad, and/or a global positioning system (GPS) receiver; and a conventional laptop and/or handheld receiver or other electronic device including a radio telephone transceiver. 
     The technical features of the above described embodiments can be combined arbitrarily. To simplify the description, not all possible combinations of the technical features in the above embodiments are described. However, all of the combinations of these technical features should be considered as within the scope of the present disclosure, as long as such combinations do not contradict with each other. 
     The above described embodiments merely represent several embodiments of the present disclosure, and the description thereof is more specific and detailed, but it should not be construed as limiting the scope of the present disclosure. It should be noted that for those of ordinary skill in the art, without departing from the concept of this disclosure, several modifications and improvements can be further made, which are all within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the appended claims.