Patent Description:
This disclosure generally relates to optical devices, and more particularly, to a lens system and an imaging device with the lens system.

Lenses play an important role in the field of security monitoring. The lenses in a camera receive rays that are reflected by an object and project the rays to an imaging sensor in the camera to generate an image of the object. The performance of the lenses may affect the image quality, which may affect the accuracy of the result in the security monitoring. The apertures and image planes of some existing lenses used in the security monitoring are relatively small, and the existing lenses cannot achieve a constant aperture, which decreases the image quality. Therefore, it is desirable to provide a lens system that can achieve a relatively large constant aperture and a relatively large image plane. <CIT> relates to a zoom lens and an imaging apparatus; <CIT> relates to a zoom lens and an imaging apparatus that uses the zoom lens suited for motion blur compensation; <CIT> relates to a zoom lens with a bent optical path and an image pickup apparatus using the same; <CIT> relates to a zoom lens; <CIT> relates to a variable power optical system, an optical device, and a method for manufacturing the variable power optical system; <CIT> relates to a zoom lens that provides a higher performance and a higher zoom ratio while having a small size; <CIT> relates to a zoom lens suitable for a surveillance camera; <CIT> relates to a projection type zoom lens and a projection type display apparatus with temperature compensation being taken into consideration.

In order to illustrate the technical solutions related to the embodiments of the present disclosure, brief introduction of the drawings referred to in the description of the embodiments is provided below. Obviously, drawings described below are only some examples or embodiments of the present disclosure. Those having ordinary skills in the art, without further creative efforts, may apply the present disclosure to other similar scenarios according to these drawings. Unless stated otherwise or obvious from the context, the same reference numeral in the drawings refers to the same structure and operation.

As used in the disclosure and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including" when used in the disclosure, specify the presence of stated steps and elements, but do not preclude the presence or addition of one or more other steps and elements.

Some modules of the system may be referred to in various ways according to some embodiments of the present disclosure, however, any number of different modules may be used and operated in a client terminal and/or a server. These modules are intended to be illustrative, not intended to limit the scope of the present disclosure. Different modules may be used in different aspects of the system and method.

According to some embodiments of the present disclosure, flow charts are used to illustrate the operations performed by the system. It is to be expressly understood, the operations above or below may or may not be implemented in order. Conversely, the operations may be performed in inverted order, or simultaneously. Besides, one or more other operations may be added to the flowcharts, or one or more operations may be omitted from the flowchart.

Technical solutions of the embodiments of the present disclosure be described with reference to the drawings as described below. It is obvious that the described embodiments are not exhaustive and are not limiting. Other embodiments obtained, based on the embodiments set forth in the present disclosure, by those with ordinary skill in the art without any creative works are within the scope of the present disclosure.

<FIG> is a schematic diagram illustrating an exemplary lens system according to some embodiments of the present disclosure.

As shown in <FIG>, the lens system <NUM> includes a first lens group G1, a second lens group G2, a third lens group G3, a fourth lens group G4, a fifth lens group G5, and an image plane <NUM> in sequence from an object side to an image side along an optical axis <NUM> of the lens system <NUM>. As used herein, the image plane <NUM> refers to a plane that is vertical to the optical axis <NUM> and includes an object's projected image generated based on the lens system <NUM>. In some embodiments, a lens group (e.g., G1-G5) may include one or more lenses. In some embodiments, at least one of G1, G2, G3, G4, and G5 may be adjustable along the optical axis <NUM> of the lens system <NUM> to change the magnification (i.e., adjust the focal length) of the lens system <NUM>. For example, G1, G3, and G5 may be fixed relative to the image plane <NUM> during the magnification change of the lens system <NUM>. G2 and G4 are adjustable along the optical axis <NUM> of the lens system <NUM> to adjust the focal length of the lens system <NUM>. In this case, G1, G3, and G5 may be referred to as first fixed lens group, second fixed lens group, and third fixed lens group, respectively. G2 may be referred to as zoom lens group and G4 may be referred to as focusing lens group.

As described above, the lens system <NUM> may have different working states (e.g., having different focal lengths). For example, the lens system <NUM> may be at a telephoto end when it is focused on an object at a maximum focal length of its zoom range. As another example, the lens system <NUM> may be at a wide-angle end when it is focused on an object at a minimum focal length of its zoom range.

The focal lengths of the lens system <NUM> satisfy formulas (<NUM>)-(<NUM>) below: <MAT> <MAT> <MAT> wherein a, b, c, d, e, and f are constants, f<NUM> represents the focal length of G2, f<NUM> represents the focal length of G3, f<NUM> represents the focal length of G4, fw represents the focal length of the lens system <NUM> at a wide-angle end, and ft represents the focal length of the lens system <NUM> at a telephoto end.

a, b, c, d, e, and f are set as specific values to ensure the size of the lens system <NUM> and/or the correction of aberrations, such as spherical aberration, coma aberration, astigmatism, field curvature, distortion, axial chromatic aberration, or lateral chromatic aberration.

a is equal to -<NUM>, b is equal to -<NUM>, c is equal to <NUM>, d is equal to <NUM>, e is equal to <NUM>, and f is equal to <NUM>. Therefore, the focal lengths of the lens system lens <NUM> satisfy formulas (<NUM>)-(<NUM>) below: <MAT> <MAT> <MAT>.

Taking formula (<NUM>) as an example, above the upper limit of formula (<NUM>), refractive power of G3 may be too weak, leading to an increase of the size of G3 (e.g., the diameter of the maximum cross-section vertical to the optical axis <NUM> of at least one lens in G3). Below the lower limit of formula (<NUM>), the refractive power of G3 may be too strong, making the aberrations of the lens system <NUM> produced at different focal lengths (e.g., the focal lengths varying from the wide-angle end to the telephoto end) difficult to be corrected. The refractive power (also referred to as optical power) refers to the degree to which an optical system (e.g., the lens system <NUM>) converges or diverges light (also referred to as rays). For example, if the optical system has positive refractive power, the optical system may converge the incident light of the optical system. If the optical system has negative refractive power, the optical system may diverge the incident light of the optical system. The larger the absolute value of the refractive power is, the larger the degree to which the optical system may converge or diverge the incident light.

In the invention, with the action of G1, G2, G3, G4, and G5, and/or the values of a, b, c, d, e, and f in formulas (<NUM>)-(<NUM>), the size of the image plane <NUM> of the lens system <NUM> may be relatively large, the maximum aperture corresponding to different focal lengths (e.g., the focal lengths varying from the wide-angle end to the telephoto end) is constant, and the size of the maximum aperture may be relatively large. In the invention, the size of the image plane is <NUM> (<NUM>/<NUM> inch). The size of the maximum aperture may be F1.

G1 has positive refractive power, G2 has negative refractive power, G3 has positive refractive power, G4 has positive refractive power, and G5 has positive refractive power.

In some embodiments, the lens system <NUM> may include at least one aspherical lens. In some embodiments, the lenses in the lens system <NUM> may be spherical lenses, which brings the benefits of low cost, high stability, suitability for mass production.

In some embodiments, the lens system <NUM> may also include one or more aperture stops (not shown in <FIG>). The aberrations (e.g., spherical aberration, astigmatism, distortion) of the lens system <NUM> may be reduced by placing one or more aperture stops in a specific location along the optical axis <NUM>. In some embodiments, the lens system <NUM> may also include one or more color filters (not shown in <FIG>) configured to correct color deviation of light incident to the lens system <NUM>.

It should be noted that the above description is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the invention as defined in the appended claims.

<FIG> is a schematic diagram illustrating an exemplary lens system according to some embodiments of the present disclosure. In some embodiments, the lens system <NUM>-<NUM> in <FIG> may be an example of the lens system <NUM> in <FIG>.

As shown in <FIG>, the lens system <NUM>-<NUM> may include a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an aperture stop <NUM>, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive refractive power, and one or more color filters <NUM> in sequence from an object side to an image side along an optical axis <NUM> of the lens system <NUM>-<NUM>. In the lens system <NUM>-<NUM>, G1, G3, and G5 may be fixed relative to the image plane <NUM> during the magnification change of the lens system <NUM>-<NUM>, and G2 and G4 may be adjustable along the optical axis <NUM> of the lens system <NUM>-<NUM> to adjust the focal length of the lens system <NUM>-<NUM>. As shown in <FIG>, the lens system <NUM>-<NUM> may limit a frist adjusting line for adjusting G2 along the optical axis <NUM> and a second adjusting line for adjusting G4 along the optical axis <NUM>. When G2 is adjusted along the optical axis <NUM> to the object-side end of the first adjusting line and G4 is adjusted along the optical axis <NUM> to the object-side end of the second adjusting line, the lens system <NUM>-<NUM> may be at the wide-angle end. When G2 is adjusted along the optical axis <NUM> to the image-side end of the first adjusting line and G4 is adjusted along the optical axis <NUM> to the image-side end of the second adjusting line, the lens system <NUM>-<NUM> may be at the telephoto end. In some embodiments, the focal lengths of the lens system lens <NUM>-<NUM> may satisfy formulas (<NUM>)-(<NUM>).

Taking the embodiment in which the lenses in the lens system <NUM>-<NUM> are spherical lenses as an example, G1 may include a first meniscus lens L11 having negative refractive power, a biconvex lens L12 having positive refractive power, and a second meniscus lens L13 having positive refractive power in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. Each of L11 and L13 may be with a convex surface toward the object side (e.g., a convex object-side surface) of the lens system <NUM>-<NUM>. A meniscus lens is a lens having two spherically curved surfaces, one convex and the other concave. A meniscus lens having positive refractive power (e.g., L13 in <FIG>) may be thicker in the middle than at the edges and serve as a converging lens. A meniscus lens having negative refractive power (e.g., L11 in <FIG>) may be thicker at the edges than in the middle and serve as a diverging lens.

In some embodiments, two or more lens may be cemented together. For example, the cementation of a lens having the positive refractive power (e.g., L12) and a lens having the negative refractive power (e.g., L11) may reduce aberrations of the lens system <NUM>, such as spherical aberration, astigmatism, axial chromatic aberration, etc. In some embodiments, L11 and L12 may be cemented together (e.g., as shown in <FIG>) or not be cemented together.

In some embodiments, G2 may include a first lens L21 having negative refractive power, a biconcave lens L22 having negative refractive power, and a second lens L23 having positive refractive power in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. L21 may be with a concave surface toward the image side (also referred to as image-side surface) of the lens system <NUM>. The surface of L21 toward the object side of the lens system <NUM> (e.g., the object-side surface of L21) may be a concave surface, a convex surface, or a plane surface. For example, L21 may be a biconcave lens (e.g., as shown in <FIG>), a plano-concave lens with a concave image-side surface and a plane object-side surface, or a meniscus lens with a concave image-side surface and a convex object-side surface. L23 may be with a convex surface toward the object side (e.g., a convex object-side surface) of the lens system <NUM>-<NUM>. The surface of L23 toward the image side (e.g., the image-side surface) of the lens system <NUM> may be a concave surface, a convex surface, or a plane surface. For example, L23 may be a biconvex lens, a plano-convex lens with a convex object-side surface and a plane image-side surface, or a meniscus lens (e.g., as shown in <FIG>) with a convex object-side surface and a concave image-side surface.

In some embodiments, G3 may include a first lens sub-group G31 having positive refractive power, a second lens sub-group G32, and a third lens sub-group G33 in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. A sub-group (e.g., G31-G33 and G41) may include one or more lenses. For example, each of G32 and G33 may include a lens having negative refractive power and a lens having positive refractive power that are cemented together.

G31 may include a first biconvex lens L31 having positive refractive power, a biconcave lens L32 having negative refractive power, and a second biconvex lens L33 having positive refractive power that are cemented together in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. G32 may include a biconcave lens L34 having negative refractive power and a biconvex lens L35 having positive refractive power that are cemented together in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. G33 may include a biconvex lens L35 having positive refractive power and a biconcave lens L36 having negative refractive power that are cemented together in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>.

In some embodiments, G4 may include a biconvex lens L41 having positive refractive power and a fourth lens sub-group G41 in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. G41 may include a lens having negative refractive power and a lens having positive refractive power that are cemented together. For example, G41 may include a biconcave lens L42 having negative refractive power and a biconvex lens L43 having positive refractive power that are cemented together in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>.

In some embodiments, G5 may include a third meniscus lens L51 having negative refractive power and a fourth meniscus lens L52 having positive refractive power in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. Each of L51 and L52 may be with a convex surface toward the object side (e.g., a convex object-side surface) of the lens system <NUM>-<NUM>. L51 and L52 may be cemented together.

In some embodiments, exemplary optical parameters of G1, G2, the aperture stop <NUM>, G3, G4, G5, and the one or more color filters <NUM> in the lens system <NUM>-<NUM> are illustrated in Table <NUM>.

Each lens in the lens system <NUM>-<NUM> may include two surfaces, an object-side surface and an image-side surface. As shown in Table <NUM>, each value in the column of "Surface Number" represents the serial number of each surface of the lenses in the lens system <NUM>-<NUM>, wherein "<NUM>" in the column of "Surface Number" represents the serial number of the object-side surface of L11 and the serial number is sequentially increased toward the image side. If two lenses are cemented together, the cemented surfaces may have a same surface number. For example, "<NUM>" in the column of "Surface Number" in Table <NUM> represents the cemented surfaces of L11 and L12 (e.g., the image-side surface of L11 and the object-side surface of L12 in <FIG>).

Each value in the column of "Radius of Curvature R (mm)" represents the radius of curvature of a corresponding lens surface. Each value in the column of "Surface Distance Tc (mm)" represents the distance along the optical axis <NUM> between a corresponding lens surface and the next lens surface. For example, "<NUM>" in the column of "Surface Distance Tc (mm)" represents the distance along the optical axis <NUM> between lens surface <NUM> (e.g., the object-side surface of L11) and lens surface <NUM> (e.g., the cemented surfaces of L11 and L12) is <NUM>. As used herein, "W" in the present disclosure represents the wide-angle end of a lens system (e.g., the lens system <NUM>, the lens system <NUM>-<NUM>, the lens system <NUM>-<NUM>), and "Ttele" in the present disclosure represents the telephoto end of the lens system. Different focus lengths of the lens system <NUM>-<NUM> may correspond to different locations of G2 and G4 along the optical axis <NUM> and different distances between G2 (or G4) and the adjacent lens group. For example, the distance between lens surface <NUM> (e.g., the image-side surface of L13 in <FIG>) and lens surface <NUM> (e.g., the object-side surface of L21 in <FIG>) is <NUM> (e.g., represented as "<NUM> (W)" in the column of "Surface Distance Tc (mm)") when the lens system <NUM>-<NUM> is at the wide-angle end. The distance between lens surface <NUM> and lens surface <NUM> is <NUM> (e.g., represented as "<NUM> (Ttele)" in the column of "Surface Distance Tc (mm)") when the lens system <NUM>-<NUM> is at the telephoto end.

Each value in the column of "Refractive Index Nd" in Table <NUM> represents the refractive index of the medium between a corresponding lens surface and the next lens surface. Each value in the column of "Abbe Number Vd" in Table <NUM> represents the Abbe number of the medium between a corresponding lens surface and the next lens surface. The Abbe number may be a measure of a medium's dispersion (variation of refractive index versus wavelength), with high values indicating low dispersion. The refractive index and the Abbe number of a lens may depend on the material of the lens.

In some embodiments, the optical parameters of the optical elements in the lens system <NUM>-<NUM> may be important to correct the aberrations of the lens system <NUM>-<NUM>. For example, spherical aberration and coma aberration of the lens system <NUM>-<NUM> may be reduced by adjusting the refractive indexes (e.g., by changing the material of the optical elements) and/or the radiuses of curvature of the optical elements in the lens system <NUM>-<NUM>. As another example, lateral chromatic aberration of the lens system <NUM>-<NUM> may be reduced by adjusting the surface distances of the optical elements in the lens system <NUM>-<NUM>.

According to the structure of the lens system <NUM>-<NUM> illustrated in <FIG> and the optical parameters illustrated in Table <NUM>, the lens system <NUM>-<NUM> may have the optical performance below:.

It should be noted that the above description is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present invention as defined in the appended claims. For example, the values of the radius of curvature, the surface distance, the refractive index, the Abbe number of each lens in the lens system <NUM>-<NUM> are not limited to the values shown in Table <NUM> and may take different values.

<FIG> and <FIG> are schematic diagrams of modulation transfer function (MTF) curve of the lens system <NUM>-<NUM> at a wide-angle end and a telephoto end, respectively, according to some embodiments of the present disclosure.

In some embodiments, a diagram of MTF curve of a lens system may assess the imaging quality of the lens system. During the process of generating the MTF curve, one or more patterns each of which includes a plurality of stripes in black alternating with white may be captured using the lens system <NUM>-<NUM>. In a pattern, the density of the black and white stripes may be represented by "spatial frequency" in line pairs per millimeter (lp/mm). Each line pair may include a black strip and the adjacent white stripe. The density of the black and white stripes in a pattern may be constant or varying. The difference between the captured pattern and the image of the captured pattern may be measured and quantified by the MTF value. The larger the MTF value is, the less the difference between the captured pattern and the image of the captured pattern may be. The MTF may be the modulus of the optical transfer function (OTF). In some embodiments, the pattern may be placed in a circle (e.g., the field of view of the lens system <NUM>-<NUM>) along the radial direction (e.g., the black and white stripes are parallel to a radial direction of the circle, or the black and white stripes radiate outwards from the center of the circle) and/or the tangential direction (e.g., the black and white stripes are vertical to a radial direction of the circle, or the black and white stripes are concentric circles of the circle). In some embodiments, the MTF values corresponding to different spatial frequencies at a location in the circle may be determined. The MTF curves may be generated based on the MTF values. The MTF curve generated based on the pattern along the radial direction may be referred to as a sagittal MTF curve. The MTF curve generated based on the pattern along the tangential direction may be referred to as a tangential MTF curve. A same location in the circle may correspond to two MTF curves, i.e., the sagittal MTF curve and the tangential MTF curve.

In some embodiments, the higher the location of an MTF curve is in the diagram (which indicates that the area under the MTF curve is larger) and the smoother the MTF curve is, the better the imaging quality of the lens system may be. The more similar the MTF curves at the wide-angle end and at the telephoto end are and the larger the average of the MTF values of the full field of view (e.g., when the spatial frequency is equal to <NUM> lp/mm as shown in <FIG> and/or <FIG>) is, the better the imaging quality of the lens system in the entire zoom focal length may be and the better the lens system may correct the aberrations, such as spherical aberration, coma aberration, astigmatism, field curvature, distortion, axial chromatic aberration, or lateral chromatic aberration.

As shown in <FIG> and <FIG>, the MTF curves are the MTF curves of visible light of which the wavelength is <NUM>-<NUM>. The horizontal axis represents spatial frequency in circles per millimeter (in lp/mm), and the vertical axis represents the modulus of the OTF (e.g., the MTF value). As shown in <FIG> and <FIG>, "T" represents the tangential MTF curve corresponding to a location and "S" represents the sagittal MTF curve corresponding to a location. "<NUM>," "<NUM>," "<NUM>," "<NUM>," and "<NUM>" represent the distances between the locations measured to generate the MTF curves and the imaging center of the field of view of the lens system <NUM>-<NUM>, respectively. As shown in <FIG>, curves <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> may be the tangential MTF curves generated, at the wide-angle end of the lens system <NUM>-<NUM>, based on locations whose distances away from the imaging center of the field of view of the lens system <NUM>-<NUM> are <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, respectively. Curves <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> may be the sagittal MTF curves generated, at the wide-angle end of the lens system <NUM>-<NUM>, based on locations whose distances away from the imaging center of the field of view of the lens system <NUM>-<NUM> are <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, respectively. As shown in <FIG>, curves <NUM>', <NUM>', <NUM>', <NUM>', and <NUM>' may be the tangential MTF curves generated, at the telephoto end of the lens system <NUM>-<NUM>, based on locations whose distances away from the imaging center of the field of view of the lens system <NUM>-<NUM> are <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, respectively. Curves <NUM>', <NUM>', <NUM>', <NUM>', and <NUM>' may be the sagittal MTF curves generated, at the telephoto end of the lens system <NUM>-<NUM>, based on locations whose distances away from the imaging center of the field of view of the lens system <NUM>-<NUM> are <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, respectively. As shown in <FIG> and <FIG>, the MTF curves at the wide-angle end and at the telephoto end are relatively similar, the averages of the MTF values of the full field of view (e.g., when the spatial frequency is equal to <NUM> lp/mm as shown in <FIG> and/or <FIG>) at the wide-angle end and at the telephoto end are relatively large (e.g., larger than a threshold value <NUM>), and the MTF curves are relatively smooth. As a result, the lens system <NUM>-<NUM> may achieve relatively high resolution and allow obtaining images with high quality. For example, the lens system <NUM>-<NUM> may be applicable to a camera with <NUM> megapixels and a <NUM>/<NUM>-inch image plane.

<FIG> and <FIG> are schematic diagrams of field curvature of the lens system <NUM>-<NUM> at a wide-angle end and a telephoto end, respectively, according to some embodiments of the present disclosure.

Field curvature may be an optical aberration in which a planar object is projected to a curved (nonplanar) image and cannot be brought properly into focus on a flat image plane. This happens due to the curved nature of optical elements (e.g., the lenses) in the lens system, which project the image in a curved manner, rather than flat. A plane including the optical axis of the lens system and a point out of the optical axis may be referred to as a tangential plane. Incident rays on the tangential plane may be referred to as tangential rays. A plane that includes the optical axis of the lens system and is vertical to the tangential plane may be referred to as a sagittal plane. Incident rays on the sagittal plane may be referred to as sagittal rays. The diagram of field curvature may indicate the aberration of the tangential rays (e.g., tangential field curvature), the aberration of the sagittal rays (e.g., sagittal field curvature), and the correction ability of field curvature of the lens system.

As shown in <FIG> and <FIG>, the horizontal axis relates to the incident height of rays from an object point with respect to the lens system <NUM>-<NUM>, and the vertical axis relates to the distance between the actual image point of the object point and the ideal image point of the object point. As shown in <FIG>, curves <NUM>, <NUM>, and <NUM> are the field curvature curves of the tangential rays (also referred to as the tangential field curvature curves) with the wavelength of <NUM>, <NUM>, and <NUM>, respectively, at the wide-angle end of the lens system <NUM>-<NUM>. Curves <NUM>, <NUM>, and <NUM> are the field curvature curves of the sagittal rays (also referred to as the sagittal field curvature curves) with the wavelength of <NUM>, <NUM>, and <NUM>, respectively, at the wide-angle end of the lens system <NUM>-<NUM>. As shown in <FIG>, the sagittal field curvature occurring in the lens system <NUM>-<NUM> at the wide-angle end is limited to a range of -<NUM>-<NUM>, and the tangential field curvature occurring in the lens system <NUM>-<NUM> at the wide-angle end is limited to a range of -<NUM>-<NUM>. As shown in <FIG>, curves <NUM>', <NUM>', and <NUM>' are the field curvature curves of the tangential rays (also referred to as the tangential field curvature curves) with the wavelength of <NUM>, <NUM>, and <NUM>, respectively, at the telephoto end of the lens system <NUM>-<NUM>. Curves <NUM>', <NUM>', and <NUM>' are the field curvature curves of the sagittal rays (also referred to as the sagittal field curvature curves) with the wavelength of <NUM>, <NUM>, and <NUM>, respectively, at the telephoto end of the lens system <NUM>-<NUM>. As shown in <FIG>, the sagittal field curvature occurring in the lens system <NUM>-<NUM> at the telephoto end is limited to a range of -<NUM>-<NUM>, and the tangential field curvature occurring in the lens system <NUM>-<NUM> at the telephoto end is limited to a range of -<NUM>-<NUM>. As a result, the field curvature of the lens system <NUM>-<NUM> may be limited to a relatively small range, which indicates that the periphery of the image plane of the lens system <NUM>-<NUM> may have relatively high resolution.

<FIG> and <FIG> are schematic diagrams illustrating axial chromatic aberration of the lens system <NUM>-<NUM> at a wide-angle end and a telephoto end, respectively, according to some embodiments of the present disclosure.

When rays with different wavelengths from an object point at the optical axis of a lens system passes through the lens system, the rays with different wavelengths may have different image points because of axial chromatic aberration, which makes an image of the object point include colored spots and/or halos. This happens due to different focal lengths of the lens system corresponding to rays with different wavelengths.

As shown in <FIG> and <FIG>, the horizontal axis relates to the incident height of rays from an object point with respect to the lens system <NUM>-<NUM>, and the vertical axis relates to the distance between the actual image point of the object point and the ideal image point of the object point. As shown in <FIG>, curves <NUM>-<NUM> are the aberration curves of the rays with the wavelengths of <NUM>, <NUM>, and <NUM>, respectively, at the wide-angle end of the lens system <NUM>-<NUM>. As shown in <FIG>, the axial chromatic aberration occurring in the lens system <NUM>-<NUM> at the wide-angle end is limited to a range of -<NUM>-<NUM>. As shown in <FIG>, curves <NUM>'-<NUM>' are the aberration curves of the rays with the wavelengths of <NUM>, <NUM>, and <NUM>, respectively, at the telephoto end of the lens system <NUM>-<NUM>. The pupil radius of the lens system <NUM>-<NUM> used to capture an object or an object point to generate curves <NUM>-<NUM> and <NUM>'-<NUM>' is <NUM>. As shown in <FIG>, the axial chromatic aberration occurring in the lens system <NUM>-<NUM> at the telephoto end is limited to a range of -<NUM>-<NUM>. As a result, the axial chromatic aberration of the lens system <NUM>-<NUM> may be limited to a relatively small range, which increases the definition of the center and the periphery of an image generated using the lens system <NUM>-<NUM>.

<FIG> and <FIG> are schematic diagrams illustrating lateral chromatic aberration of the lens system <NUM>-<NUM> at a wide-angle end and a telephoto end, respectively, according to some embodiments of the present disclosure.

Lateral chromatic aberration may be an optical aberration in which an image of an object has colored edges and poor definition. This is caused by the fact that rays of different wavelengths are not equally refracted by the lens system, so that rays of different wavelengths from a same point (e.g., a point out of the optical axis of the lens system) corresponds to different image heights.

As shown in <FIG> and <FIG>, the horizontal axis relates to the incident height of rays from an object point to the lens system <NUM>-<NUM>, and the vertical axis relates to the distance between the actual image point of the object point and the ideal image point of the object point. The maximum field of the lens system <NUM>-<NUM> used to capture an object or an object point to generate curves <NUM>-<NUM> and <NUM>'-<NUM>' is <NUM>. As shown in <FIG>, curves <NUM>-<NUM> are the aberration curves of the rays with the wavelengths of <NUM>, <NUM>, and <NUM>, respectively, at the wide-angle end of the lens system <NUM>-<NUM>. Curves <NUM> and <NUM> are generated by determining curve <NUM> as a reference curve. In this case, at the wide-angle end, it is assumed that the actual image point of the object point and the ideal image point of the object point corresponding to the rays with the wavelengths of <NUM> is overlapped at any incident height. As shown in <FIG>, the lateral chromatic aberration occurring in the lens system <NUM>-<NUM> at the wide-angle end is limited to a range of -<NUM>-<NUM>. As shown in <FIG>, curves <NUM>'-<NUM>' are the aberration curves of the rays with the wavelengths of <NUM>, <NUM>, and <NUM>, respectively, at the telephoto end of the lens system <NUM>-<NUM>. Curves <NUM>' and <NUM>' are generated by determining curve <NUM>' as a reference curve. In this case, at the telephoto end, it is assumed that the actual image point of the object point and the ideal image point of the object point corresponding to the rays with the wavelengths of <NUM> is overlapped at any incident height. As shown in <FIG>, the lateral chromatic aberration occurring in the lens system <NUM>-<NUM> at the telephoto end is limited to a range of -<NUM>-<NUM>. As a result, the lateral chromatic aberration of the lens system <NUM>-<NUM> may be limited to a relatively small range, which increases the definition of the center and the periphery of an image generated using the lens system <NUM>-<NUM>.

As illustrated above, the lens system <NUM>-<NUM> may well correct the aberrations, such as spherical aberration, coma aberration, astigmatism, field curvature, distortion, axial chromatic aberration, or lateral chromatic aberration. The lens system <NUM>-<NUM> may have a larger aperture (e.g., F1. <NUM>) and higher resolution (e.g., applicable to a camera with <NUM> megapixels). The lens system <NUM>-<NUM> may be applicable to capturing ultra high-definition (HD) images and/or video in all weather conditions in the field of, for example, security monitoring.

As shown in <FIG>, the lens system <NUM>-<NUM> may include a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an aperture stop <NUM>, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having positive refractive power, and one or more color filters <NUM> in sequence from an object side to an image side along an optical axis <NUM> of the lens system <NUM>-<NUM>. G1, G3, and G5 may be fixed relative to the image plane <NUM> during the magnification change of the lens system <NUM>-<NUM>. G2 and G4 may be adjustable along the optical axis <NUM> of the lens system <NUM>-<NUM> to adjust the focal length of the lens system <NUM>-<NUM>. As shown in <FIG>, the lens system <NUM>-<NUM> may limit a third adjusting line for adjusting G2 along the optical axis <NUM> and a fourth adjusting line for adjusting G4 along the optical axis <NUM>. When G2 is adjusted along the optical axis <NUM> to the object-side end of the third adjusting line and G4 is adjusted along the optical axis <NUM> to the image-side end of the fourth adjusting line, the lens system <NUM>-<NUM> may be at the wide-angle end. When G2 is adjusted along the optical axis <NUM> to the image-side end of the third adjusting line and G4 is adjusted along the optical axis <NUM> to the object-side end of the fourth adjusting line, the lens system <NUM>-<NUM> may be at the telephoto end. In some embodiments, the lens system lens <NUM>-<NUM> may satisfy formulas (<NUM>)-(<NUM>).

In some embodiments, G3 may include a first lens sub-group G31 having positive refractive power, a second lens sub-group G32, and a third lens sub-group G33 in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. G31 may include a biconvex lens L31' having positive refractive power and a meniscus lens L32' having positive refractive power in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. The object-side surface of L32' may be a convex surface (e.g., as shown in <FIG>) or a concave surface. If the object-side surface of L32' is the concave surface, L31' and L32' may be cemented together. G32 may include a biconcave lens L33' having negative refractive power and a biconvex lens L34' having positive refractive power that are cemented together in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. G33 may include a meniscus lens L35' having positive refractive power and a biconcave lens L36' having negative refractive power in sequence from the object side to the image side along the optical axis <NUM> of the lens system <NUM>-<NUM>. The object-side surface of L35' may be a convex surface or a concave surface (e.g., as shown in <FIG>). If the object-side surface of L35' is the concave surface, L35' and L36' may be cemented together.

In the lens system <NUM>-<NUM>, the structure of G1, G2, G4, and G5 may be similar to the lens system <NUM>-<NUM> in <FIG> and is not described in <FIG>.

It should be noted that the above description is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present invention as defined in the appended claims.

In some embodiments, the lens systems (e.g., the lens system <NUM>, the lens system <NUM>-<NUM>, the lens system <NUM>-<NUM>) described in the present disclosure may be used in an imaging device, such as a digital camera, a web camera, a video gaming console equipped with a web camera, a video camera, a motion picture camera, a broadcasting camera, or a closed circuit television (CCTV) camera. In the imaging device, an image sensor, such as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), may receive rays that are reflected by an object and pass through the lens system, and transform the rays from light signals to electronic signals. An analog-digital converter (ADC) in the imaging device may transform the electronic signals to digital signals. Image processing circuits in the imaging device may process the digital signals to generate an image of the object. A storage medium in the imaging device may record the generated image. With the imaging device, a still image, a moving image, or a video may be captured. The imaging device that is provided with the lens system in the present disclosure may achieve a high image stabilization effect and allow obtaining high quality images.

Having thus described the basic concepts, it may be rather apparent to those skilled in the art after reading this detailed disclosure that the foregoing detailed disclosure is intended to be presented by way of example only and is not limiting. Various alterations, improvements, and modifications may occur and are intended to those skilled in the art, though not expressly stated herein.

For example, the terms "one embodiment," "an embodiment," and "some embodiments" mean that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure.

Claim 1:
A lens system comprising a first lens group, a second lens group, a third lens group, a fourth lens group, and a fifth lens group in sequence from an object side to an image side along an optical axis of the lens system, wherein:
the first lens group has positive refractive power, the second lens group has negative refractive power, the third lens group has positive refractive power, the fourth lens group has positive refractive power, and the fifth lens group has positive refractive power;
the second lens groups and the fourth lens group are adjustable along the optical axis of the lens system to adjust a focal length of the lens system; and characterized in that the lens system satisfies <MAT> so as to realize a desired image quality, the lens system having an image plane with a size of <NUM> (<NUM>/<NUM> inch) and a constant maximum aperture corresponding to focal lengths from a wide-angle end to a telephoto end;
wherein f<NUM> represents a focal length of the second lens group, f<NUM> represents a focal length of the third lens group, f<NUM> represents a focal length of the fourth lens group, fw represents a focal length of the lens system at the wide-angle end, and ft represents a focal length of the lens system at the telephoto end.