Patent Publication Number: US-11644646-B2

Title: Optical imaging lens

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of the application Ser. No. 16/425,843, filed on May 29, 2019, which is a continuation of the application Ser. No. 15/880,551, filed on Jan. 26, 2018, which claims priority to Chinese Patent Application No. 201711477746.1, filed on Dec. 29, 2017. The contents thereof are included herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an optical imaging lens. Specifically speaking, the present invention is directed to an optical imaging lens for use in portable electronic devices such as mobile phones, cameras, tablet personal computers, or personal digital assistants (PDA) for taking pictures and for recording videos, and for use in the field of detection of 3D images. 
     2. Description of the Prior Art 
     In recent years, the optical imaging lenses evolve and the application is getting wider and wider. In addition to being lighter, thinner, shorter and smaller, it is better to increase the luminous flux with the design of a smaller f-number. Accordingly, it is an important objective to develop an optical imaging lens not only to be lighter, thinner, shorter and smaller at the same time but also to have an optical imaging lens with a small f-number and with good imaging quality. 
     SUMMARY OF THE INVENTION 
     In light of the above, an embodiment of the present invention proposes an optical imaging lens of four lens elements which has reduced optical imaging lens system length, ensured imaging quality, a smaller f-number, good optical performance and is technically possible. The optical imaging lens of four lens elements of the present invention from an object side to an image side in order along an optical axis has a first lens element, a second lens element, a third lens element and a fourth lens element. Each one of the first lens element, the second lens element, the third lens element and the fourth lens element respectively has an object-side surface which faces toward the object side to allow imaging rays to pass through as well as an image-side surface which faces toward the image side to allow the imaging rays to pass through. 
     In one embodiment of the present invention, the optical-axis region of the image-side surface of the first lens element is concave. The periphery region of the image-side surface of the second lens element is convex. The third lens has positive refracting power and the optical-axis region of the object-side surface of the fourth lens element is convex. Lens elements having refracting power included by the optical imaging lens are only the four lens elements described above. The Abbe number of the first lens element is υ1, the Abbe number of the second lens element is υ2, the Abbe number of the third lens element is υ3 and the Abbe number of the fourth lens element is υ4 to satisfy υ2≤30.000 and (υ1+υ3+υ4)≤120.000. 
     In the optical imaging lens of the present invention, the embodiments further satisfy the following relationships:
 
 ALT/BFL≥ 1.200;
 
 AAG/G 23≤2.200;
 
 EFL /( T 1+ T 3)≤3.500;
 
( T 2+ T 3)/ T 1≥1.800;
 
( T 3+ T 4)/( G 23+ G 34)≤3.500;
 
( T 1+ T 2)/( G 12+ G 23)≤2.800;
 
 BFL /( G 34+ T 4)≤3.100;
 
 TL /( T 1+ G 12)≥3.200;
 
 EFL/AAG≤ 3.900;
 
 TTL /( T 3+ T 4)≥3.800;
 
 ALT/T 2≤4.800;
 
( T 4+ BFL )/ T 3≤4.500;
 
 T 2/ T 1≥1.000;
 
 ALT/AAG≤ 4.500;
 
 TL/BFL≥ 1.800;
 
( T 2+ T 3+ T 4)/ T 1≥2.500;
 
( T 1+ T 3+ T 4)/ T 2≤3.500;
 
 EFL /( T 2+ G 23)≤3.000; and
 
 ALT/T 13≥0.500.
 
     T1 is a thickness of the first lens element along the optical axis, T2 is a thickness of the second lens element along the optical axis, T3 is a thickness of the third lens element along the optical axis, T4 is a thickness of the fourth lens element along the optical axis, G12 is an air gap between the first lens element and the second lens element along the optical axis, G23 is an air gap between the second lens element and the third lens element along the optical axis, G34 is an air gap between the third lens element and the fourth lens element along the optical axis. 
     TTL is a distance from the object-side surface of the first lens element to an image plane along the optical axis, TL is a distance from the object-side surface of the first lens element to the image-side surface of the fourth lens element along the optical axis, ALT is a sum of thickness of all the four lens elements along the optical axis, AAG is a sum of three air gaps from the first lens element to the fourth lens element along the optical axis, EFL is an effective focal length of the optical imaging lens and BFL is a distance from the image-side surface of the fourth lens element to an image plane along the optical axis. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 - 5    illustrate the methods for determining the surface shapes and for determining an optical axis region and a periphery region of one lens element. 
         FIG.  6    illustrates a first embodiment of the optical imaging lens of the present invention. 
         FIG.  7 A  illustrates the longitudinal spherical aberration on the image plane of the first embodiment. 
         FIG.  7 B  illustrates the field curvature on the sagittal direction of the first embodiment. 
         FIG.  7 C  illustrates the field curvature on the tangential direction of the first embodiment. 
         FIG.  7 D  illustrates the distortion of the first embodiment. 
         FIG.  8    illustrates a second embodiment of the optical imaging lens of the present invention. 
         FIG.  9 A  illustrates the longitudinal spherical aberration on the image plane of the second embodiment. 
         FIG.  9 B  illustrates the field curvature on the sagittal direction of the second embodiment. 
         FIG.  9 C  illustrates the field curvature on the tangential direction of the second embodiment. 
         FIG.  9 D  illustrates the distortion of the second embodiment. 
         FIG.  10    illustrates a third embodiment of the optical imaging lens of the present invention. 
         FIG.  11 A  illustrates the longitudinal spherical aberration on the image plane of the third embodiment. 
         FIG.  11 B  illustrates the field curvature on the sagittal direction of the third embodiment. 
         FIG.  11 C  illustrates the field curvature on the tangential direction of the third embodiment. 
         FIG.  11 D  illustrates the distortion of the third embodiment. 
         FIG.  12    illustrates a fourth embodiment of the optical imaging lens of the present invention. 
         FIG.  13 A  illustrates the longitudinal spherical aberration on the image plane of the fourth embodiment. 
         FIG.  13 B  illustrates the field curvature on the sagittal direction of the fourth embodiment. 
         FIG.  13 C  illustrates the field curvature on the tangential direction of the fourth embodiment. 
         FIG.  13 D  illustrates the distortion of the fourth embodiment. 
         FIG.  14    illustrates a fifth embodiment of the optical imaging lens of the present invention. 
         FIG.  15 A  illustrates the longitudinal spherical aberration on the image plane of the fifth embodiment. 
         FIG.  15 B  illustrates the field curvature on the sagittal direction of the fifth embodiment. 
         FIG.  15 C  illustrates the field curvature on the tangential direction of the fifth embodiment. 
         FIG.  15 D  illustrates the distortion of the fifth embodiment. 
         FIG.  16    illustrates a sixth embodiment of the optical imaging lens of the present invention. 
         FIG.  17 A  illustrates the longitudinal spherical aberration on the image plane of the sixth embodiment. 
         FIG.  17 B  illustrates the field curvature on the sagittal direction of the sixth embodiment. 
         FIG.  17 C  illustrates the field curvature on the tangential direction of the sixth embodiment. 
         FIG.  17 D  illustrates the distortion of the sixth embodiment. 
         FIG.  18    illustrates a seventh embodiment of the optical imaging lens of the present invention. 
         FIG.  19 A  illustrates the longitudinal spherical aberration on the image plane of the seventh embodiment. 
         FIG.  19 B  illustrates the field curvature on the sagittal direction of the seventh embodiment. 
         FIG.  19 C  illustrates the field curvature on the tangential direction of the seventh embodiment. 
         FIG.  19 D  illustrates the distortion of the seventh embodiment. 
         FIG.  20    shows the optical data of the first embodiment of the optical imaging lens. 
         FIG.  21    shows the aspheric surface data of the first embodiment. 
         FIG.  22    shows the optical data of the second embodiment of the optical imaging lens. 
         FIG.  23    shows the aspheric surface data of the second embodiment. 
         FIG.  24    shows the optical data of the third embodiment of the optical imaging lens. 
         FIG.  25    shows the aspheric surface data of the third embodiment. 
         FIG.  26    shows the optical data of the fourth embodiment of the optical imaging lens. 
         FIG.  27    shows the aspheric surface data of the fourth embodiment. 
         FIG.  28    shows the optical data of the fifth embodiment of the optical imaging lens. 
         FIG.  29    shows the aspheric surface data of the fifth embodiment. 
         FIG.  30    shows the optical data of the sixth embodiment of the optical imaging lens. 
         FIG.  31    shows the aspheric surface data of the sixth embodiment. 
         FIG.  32    shows the optical data of the seventh embodiment of the optical imaging lens. 
         FIG.  33    shows the aspheric surface data of the seventh embodiment. 
         FIG.  34    shows some important ratios in the embodiments. 
         FIG.  35    shows some important ratios in the embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the present disclosure, the optical system may comprise at least one lens element to receive imaging rays that are incident on the optical system over a set of angles ranging from parallel to an optical axis to a half field of view (HFOV) angle with respect to the optical axis. The imaging rays pass through the optical system to produce an image on an image plane. The term “a lens element having positive refracting power (or negative refracting power)” means that the paraxial refracting power of the lens element in Gaussian optics is positive (or negative). The term “an object-side (or image-side) surface of a lens element” refers to a specific region of that surface of the lens element at which imaging rays can pass through that specific region. Imaging rays include at least two types of rays: a chief ray Lc and a marginal ray Lm (as shown in  FIG.  1   ). An object-side (or image-side) surface of a lens element can be characterized as having several regions, including an optical axis region, a periphery region, and, in some cases, one or more intermediate regions, as discussed more fully below. 
       FIG.  1    is a radial cross-sectional view of a lens element  100 . Two referential points for the surfaces of the lens element  100  can be defined: a central point, and a transition point. The central point of a surface of a lens element is a point of intersection of that surface and the optical axis I. As illustrated in  FIG.  1   , a first central point CP 1  may be present on the object-side surface  110  of lens element  100  and a second central point CP 2  may be present on the image-side surface  120  of the lens element  100 . The transition point is a point on a surface of a lens element, at which the line tangent to that point is perpendicular to the optical axis I. The optical boundary OB of a surface of the lens element is defined as a point at which the radially outermost marginal ray Lm passing through the surface of the lens element intersects the surface of the lens element. All transition points lie between the optical axis I and the optical boundary OB of the surface of the lens element. If multiple transition points are present on a single surface, then these transition points are sequentially named along the radial direction of the surface with reference numerals starting from the first transition point. For example, the first transition point, e.g., TP 1 , (closest to the optical axis I), the second transition point, e.g., TP 2 , (as shown in  FIG.  4   ), and the Nth transition point (farthest from the optical axis I). 
     The region of a surface of the lens element from the central point to the first transition point TP 1  is defined as the optical axis region, which includes the central point. The region located radially outside of the farthest N th  transition point from the optical axis I to the optical boundary OB of the surface of the lens element is defined as the periphery region. In some embodiments, there may be intermediate regions present between the optical axis region and the periphery region, with the number of intermediate regions depending on the number of the transition points. 
     The shape of a region is convex if a collimated ray being parallel to the optical axis I and passing through the region is bent toward the optical axis I such that the ray intersects the optical axis I on the image side A 2  of the lens element. The shape of a region is concave if the extension line of a collimated ray being parallel to the optical axis I and passing through the region intersects the optical axis I on the object side A 1  of the lens element. 
     Additionally, referring to  FIG.  1   , the lens element  100  may also have a mounting portion  130  extending radially outward from the optical boundary OB. The mounting portion  130  is typically used to physically secure the lens element to a corresponding element of the optical system (not shown). Imaging rays do not reach the mounting portion  130 . The structure and shape of the mounting portion  130  are only examples to explain the technologies, and should not be taken as limiting the scope of the present disclosure. The mounting portion  130  of the lens elements discussed below may be partially or completely omitted in the following drawings. 
     Referring to  FIG.  2   , optical axis region Z 1  is defined between central point CP and first transition point TP 1 . Periphery region Z 2  is defined between TP 1  and the optical boundary OB of the surface of the lens element. Collimated ray  211  intersects the optical axis I on the image side A 2  of lens element  200  after passing through optical axis region Z 1 , i.e., the focal point of collimated ray  211  after passing through optical axis region Z 1  is on the image side A 2  of the lens element  200  at point R in  FIG.  2   . Accordingly, since the ray itself intersects the optical axis I on the image side A 2  of the lens element  200 , optical axis region Z 1  is convex. On the contrary, collimated ray  212  diverges after passing through periphery region Z 2 . The extension line EL of collimated ray  212  after passing through periphery region Z 2  intersects the optical axis I on the object side A 1  of lens element  200 , i.e., the focal point of collimated ray  212  after passing through periphery region Z 2  is on the object side A 1  at point M in  FIG.  2   . Accordingly, since the extension line EL of the ray intersects the optical axis I on the object side A 1  of the lens element  200 , periphery region Z 2  is concave. In the lens element  200  illustrated in  FIG.  2   , the first transition point TP 1  is the border of the optical axis region and the periphery region, i.e., TP 1  is the point at which the shape changes from convex to concave. 
     Alternatively, there is another way for a person having ordinary skill in the art to determine whether an optical axis region is convex or concave by referring to the sign of “Radius” (the “R” value), which is the paraxial radius of shape of a lens surface in the optical axis region. The R value is commonly used in conventional optical design software such as Zemax and CodeV. The R value usually appears in the lens data sheet in the software. For an object-side surface, a positive R value defines that the optical axis region of the object-side surface is convex, and a negative R value defines that the optical axis region of the object-side surface is concave. Conversely, for an image-side surface, a positive R value defines that the optical axis region of the image-side surface is concave, and a negative R value defines that the optical axis region of the image-side surface is convex. The result found by using this method should be consistent with the method utilizing intersection of the optical axis by rays/extension lines mentioned above, which determines surface shape by referring to whether the focal point of a collimated ray being parallel to the optical axis I is on the object-side or the image-side of a lens element. As used herein, the terms “a shape of a region is convex (concave),” “a region is convex (concave),” and “a convex-(concave-) region,” can be used alternatively. 
       FIG.  3   ,  FIG.  4    and  FIG.  5    illustrate examples of determining the shape of lens element regions and the boundaries of regions under various circumstances, including the optical axis region, the periphery region, and intermediate regions as set forth in the present specification. 
       FIG.  3    is a radial cross-sectional view of a lens element  300 . As illustrated in  FIG.  3   , only one transition point TP 1  appears within the optical boundary OB of the image-side surface  320  of the lens element  300 . Optical axis region Z 1  and periphery region Z 2  of the image-side surface  320  of lens element  300  are illustrated. The R value of the image-side surface  320  is positive (i.e., R&gt;0). Accordingly, the optical axis region Z 1  is concave. 
     In general, the shape of each region demarcated by the transition point will have an opposite shape to the shape of the adjacent region(s). Accordingly, the transition point will define a transition in shape, changing from concave to convex at the transition point or changing from convex to concave. In  FIG.  3   , since the shape of the optical axis region Z 1  is concave, the shape of the periphery region Z 2  will be convex as the shape changes at the transition point TP 1 . 
       FIG.  4    is a radial cross-sectional view of a lens element  400 . Referring to  FIG.  4   , a first transition point TP 1  and a second transition point TP 2  are present on the object-side surface  410  of lens element  400 . The optical axis region Z 1  of the object-side surface  410  is defined between the optical axis I and the first transition point TP 1 . The R value of the object-side surface  410  is positive (i.e., R&gt;0). Accordingly, the optical axis region Z 1  is convex. 
     The periphery region Z 2  of the object-side surface  410 , which is also convex, is defined between the second transition point TP 2  and the optical boundary OB of the object-side surface  410  of the lens element  400 . Further, intermediate region Z 3  of the object-side surface  410 , which is concave, is defined between the first transition point TP 1  and the second transition point TP 2 . Referring once again to  FIG.  4   , the object-side surface  410  includes an optical axis region Z 1  located between the optical axis I and the first transition point TP 1 , an intermediate region Z 3  located between the first transition point TP 1  and the second transition point TP 2 , and a periphery region Z 2  located between the second transition point TP 2  and the optical boundary OB of the object-side surface  410 . Since the shape of the optical axis region Z 1  is designed to be convex, the shape of the intermediate region Z 3  is concave as the shape of the intermediate region Z 3  changes at the first transition point TP 1 , and the shape of the periphery region Z 2  is convex as the shape of the periphery region Z 2  changes at the second transition point TP 2 . 
       FIG.  5    is a radial cross-sectional view of a lens element  500 . Lens element  500  has no transition point on the object-side surface  510  of the lens element  500 . For a surface of a lens element with no transition point, for example, the object-side surface  510  the lens element  500 , the optical axis region Z 1  is defined as the region between 0-50% of the distance between the optical axis I and the optical boundary OB of the surface of the lens element and the periphery region is defined as the region between 50%-100% of the distance between the optical axis I and the optical boundary OB of the surface of the lens element. Referring to lens element  500  illustrated in  FIG.  5   , the optical axis region Z 1  of the object-side surface  510  is defined between the optical axis I and 50% of the distance between the optical axis I and the optical boundary OB. The R value of the object-side surface  510  is positive (i.e., R&gt;0). Accordingly, the optical axis region Z 1  is convex. For the object-side surface  510  of the lens element  500 , because there is no transition point, the periphery region Z 2  of the object-side surface  510  is also convex. It should be noted that lens element  500  may have a mounting portion (not shown) extending radially outward from the periphery region Z 2 . 
     As shown in  FIG.  6   , the optical imaging lens  1  of four lens elements of the present invention, sequentially located from an object side  2  (where an object is located) to an image side  3  along an optical axis  4 , has a first lens element  10 , an aperture stop (ape. stop)  80 , a second lens element  20 , a third lens element  30 , a fourth lens element  40  and an image plane  71 . Generally speaking, the first lens element  10 , the second lens element  20 , the third lens element  30  and the fourth lens element  40  may be made of a transparent plastic material but the present invention is not limited to this. Each lens element has an appropriate refracting power. In the present invention, the lens elements having refracting power included by the optical imaging lens  1  are only the four lens elements as described above. The optical axis  4  is the optical axis of the entire optical imaging lens  1 , and the optical axis  4  of each of the lens elements coincides with the optical axis  4  of the optical imaging lens  1 . 
     Furthermore, the optical imaging lens  1  includes an aperture stop (ape. stop)  80  disposed in an appropriate position. In  FIG.  6   , the aperture stop  80  is disposed between the first lens element  10  and the second lens element  20 . When light emitted or reflected by an object (not shown) which is located at the object side  2  enters the optical imaging lens  1  of the present invention, it forms a clear and sharp image on the image plane  71  at the image side  3  after passing through the first lens element  10 , the aperture stop  80 , the second lens element  20 , the third lens element  30 , the fourth lens element  40  and the optional filter  70 . In the embodiments of the present invention, the optional setting filter  70  is disposed between the image-side surface  42  of the fourth lens element  40  and the image plane  71 . In one embodiment of the present invention, the optional setting filter  70  may be a filter of various suitable functions, for example, the filter  70  may be a filter to allow light of specific wavelength (such as IR or visible light) to pass through. 
     Each lens element in the optical imaging lens  1  of the present invention has an object-side surface facing toward the object side  2  and allowing imaging rays to pass through as well as an image-side surface facing toward the image side  3  and allowing the imaging rays to pass through. In addition, each object-side surface and image-side surface in the optical imaging lens  1  of the present invention has an optical axis region and a periphery region. For example, the first lens element  10  has an object-side surface  11  and an image-side surface  12 ; the second lens element  20  has an object-side surface  21  and an image-side surface  22 ; the third lens element  30  has an object-side surface  31  and an image-side surface  32 ; the fourth lens element  40  has an object-side surface  41  and an image-side surface  42 . 
     Each lens element in the optical imaging lens  1  of the present invention further has a thickness T along the optical axis  4 . For example, the first lens element  10  has a first lens element thickness T1, the second lens element  20  has a second lens element thickness T2, the third lens element  30  has a third lens element thickness T3, the fourth lens element  40  has a fourth lens element thickness T4. Therefore, the sum of the thickness of all the four lens elements in the optical imaging lens  1  along the optical axis  4  is ALT=T1+T2+T3+T4. 
     In addition, between two adjacent lens elements in the optical imaging lens  1  of the present invention there may be an air gap along the optical axis  4 . For example, there is an air gap G12 disposed between the first lens element  10  and the second lens element  20 , an air gap G23 disposed between the second lens element  20  and the third lens element  30 , an air gap G34 disposed between the third lens element  30  and the fourth lens element  40 . Therefore, the sum of three air gaps from the first lens element  10  to the fourth lens element  40  along the optical axis  4  is AAG=G12+G23+G34. 
     In addition, the distance from the object-side surface  11  of the first lens element  10  to the image plane  71 , namely the total length of the optical imaging lens along the optical axis  4  is TTL; the effective focal length of the optical imaging lens is EFL; the distance from the image-side surface  42  of fourth lens element  40  to the image plane  71  along the optical axis  4  is BFL; the distance from the object-side surface  11  of the first lens element  10  to the image-side surface  42  of the fourth lens element  40  along the optical axis  4  is TL. 
     When the filter  70  is disposed between the fourth lens element  40  and the image plane  71 , the distance from the image-side surface  42  of the fourth lens element  40  to the filter  70  along the optical axis  4  is G4F; the thickness of the filter  70  along the optical axis  4  is TF; the distance from the filter  70  to the image plane  71  along the optical axis  4  is GFP; and the distance from the image-side surface  42  of the fourth lens element  40  to the image plane  71  along the optical axis  4  is BFL. Therefore, BFL=G4F+TF+GFP. 
     Furthermore, the focal length of the first lens element  10  is f1; the focal length of the second lens element  20  is f2; the focal length of the third lens element  30  is f3; the focal length of the fourth lens element  40  is f4; the refractive index of the first lens element  10  is n1; the refractive index of the second lens element  20  is n2; the refractive index of the third lens element  30  is n3; the refractive index of the fourth lens element  40  is n4; the Abbe number of the first lens element  10  is υ1; the Abbe number of the second lens element  20  is 12; the Abbe number of the third lens element  30  is υ3; and the Abbe number of the fourth lens element  40  is υ4. 
     First Embodiment 
     Please refer to  FIG.  6    which illustrates the first embodiment of the optical imaging lens  1  of the present invention. Please refer to  FIG.  7 A  for the longitudinal spherical aberration on the image plane  71  of the first embodiment; please refer to  FIG.  7 B  for the field curvature on the sagittal direction; please refer to  FIG.  7 C  for the field curvature on the tangential direction; and please refer to  FIG.  7 D  for the distortion aberration. The Y axis of the spherical aberration in each embodiment is “field of view” for 1.0. The Y axis of the field curvature and the distortion aberration in each embodiment stands for “image height”, IMH, which is 1.500 mm. 
     The optical imaging lens  1  of the first embodiment exclusively has four lens elements  10 ,  20 ,  30  and  40  with refracting power. The optical imaging lens  1  also has an aperture stop  80  and an image plane  71 . The aperture stop  80  is provided between the first lens element  10  and the second lens element  20 . 
     The first lens element  10  has negative refracting power. An optical axis region  13  of the object-side surface  11  facing toward the object side  2  is convex, and a periphery region  14  of the object-side surface  11  facing toward the object side  2  is convex. An optical axis region  16  of the image-side surface  12  facing toward the image side  3  is concave, and a periphery region  17  of the image-side surface  12  facing toward the image side  3  is concave. Besides, both the object-side surface  11  and the image-side  12  of the first lens element  10  are aspherical surfaces but the present invention is not limited to these. 
     The second lens element  20  has positive refracting power. An optical axis region  23  of the object-side surface  21  facing toward the object side  2  is convex, and a periphery region  24  of the object-side surface  21  facing toward the object side  2  is convex. An optical axis region  26  of the image-side surface  22  facing toward the image side  3  is convex, and a periphery region  27  of the image-side surface  22  facing toward the image side  3  is convex. Besides, both the object-side surface  21  and the image-side  22  of the second lens element  20  are aspherical surfaces but the present invention is not limited to these. 
     The third lens element  30  has positive refracting power. An optical axis region  33  of the object-side surface  31  facing toward the object side  2  is concave, and a periphery region  34  of the object-side surface  31  facing toward the object side  2  is concave. An optical axis region  36  of the image-side surface  32  facing toward the image side  3  is convex, and a periphery region  37  of the image-side surface  32  facing toward the image side  3  is convex. Besides, both the object-side surface  31  and the image-side  32  of the third lens element  30  are aspherical surfaces but the present invention is not limited to these. 
     The fourth lens element  40  has positive refracting power. An optical axis region  43  of the object-side surface  41  facing toward the object side  2  is convex, and a periphery region  44  of the object-side surface  41  facing toward the object side  2  is concave. An optical axis region  46  of the image-side surface  42  facing toward the image side  3  is concave, and a periphery region  47  of the image-side surface  42  facing toward the image side  3  is convex. Besides, both the object-side surface  41  and the image-side  42  of the fourth lens element  40  are aspherical surfaces but the present invention is not limited to these. 
     In the first lens element  10 , the second lens element  20 , the third lens element  30  and the fourth lens element  40  of the optical imaging lens element  1  of the present invention, there are 8 surfaces, such as the object-side surfaces  11 / 21 / 31 / 41  and the image-side surfaces  12 / 22 / 32 / 42 . If a surface is aspherical, these aspheric coefficients are defined according to the following formula: 
     
       
         
           
             
               Z 
               ⁡ 
               ( 
               Y 
               ) 
             
             = 
             
               
                 
                   
                     Y 
                     2 
                   
                   R 
                 
                 / 
                 
                   ( 
                   
                     1 
                     + 
                     
                       
                         1 
                         - 
                         
                           
                             ( 
                             
                               1 
                               + 
                               K 
                             
                             ) 
                           
                           ⁢ 
                           
                             
                               Y 
                               2 
                             
                             
                               R 
                               2 
                             
                           
                         
                       
                     
                   
                   ) 
                 
               
               + 
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   n 
                 
                 
                   
                     a 
                     
                       2 
                       ⁢ 
                       i 
                     
                   
                   × 
                   
                     Y 
                     
                       2 
                       ⁢ 
                       i 
                     
                   
                 
               
             
           
         
       
     
     In which: 
     R represents the curvature radius of the lens element surface; 
     Z represents the depth of an aspherical surface (the perpendicular distance between the point of the aspherical surface at a distance Y from the optical axis and the tangent plane of the vertex on the optical axis of the aspherical surface); 
     Y represents a vertical distance from a point on the aspherical surface to the optical axis; 
     K is a conic constant; and 
     a 2i  is the aspheric coefficient of the 2i th  order. 
     The optical data of the first embodiment of the optical imaging lens  1  are shown in  FIG.  20    while the aspheric surface data are shown in  FIG.  21   . In the present embodiments of the optical imaging lens, the f-number of the entire optical imaging lens element system is Fno, EFL is the effective focal length, HFOV stands for the half field of view which is half of the field of view of the entire optical imaging lens element system, and the unit for the curvature radius, the thickness and the focal length is in millimeters (mm). In this embodiment, image height=1.500 mm; EFL=2.108 mm; HFOV=34.216 degrees; TTL=3.272 mm; Fno=1.5. 
     Second Embodiment 
     Please refer to  FIG.  8    which illustrates the second embodiment of the optical imaging lens  1  of the present invention. It is noted that from the second embodiment to the following embodiments, in order to simplify the figures, only the components different from what the first embodiment has, and the basic lens elements will be labeled in figures. Other components that are the same as what the first embodiment has, such as the object-side surface, the image-side surface, the optical axis region and the periphery region will be omitted in the following embodiments. Please refer to  FIG.  9 A  for the longitudinal spherical aberration on the image plane  71  of the second embodiment, please refer to  FIG.  9 B  for the field curvature on the sagittal direction, please refer to  FIG.  9 C  for the field curvature on the tangential direction, and please refer to  FIG.  9 D  for the distortion. The components in this embodiment are similar to those in the first embodiment, but the optical data such as the curvature radius, the lens thickness, the aspheric surface or the back focal length in this embodiment are different from the optical data in the first embodiment. Besides, in this embodiment, the first lens element  10  has positive refracting power and the fourth lens element  40  has negative refracting power. 
     The optical data of the second embodiment of the optical imaging lens are shown in  FIG.  22    while the aspheric surface data are shown in  FIG.  23   . In this embodiment, image height=1.500 mm; EFL=2.274 mm; HFOV=32.831 degrees; TTL=3.328 mm; Fno=1.5. In particular, 1. the longitudinal spherical aberration and the distortion of the optical imaging lens in this embodiment are better than those of the optical imaging lens in the first embodiment, and 2. the fabrication of this embodiment is easier than that of the first embodiment so the yield is better. 
     Third Embodiment 
     Please refer to  FIG.  10    which illustrates the third embodiment of the optical imaging lens  1  of the present invention. Please refer to  FIG.  11 A  for the longitudinal spherical aberration on the image plane  71  of the third embodiment; please refer to  FIG.  11 B  for the field curvature on the sagittal direction; please refer to  FIG.  11 C  for the field curvature on the tangential direction; and please refer to  FIG.  11 D  for the distortion. The components in this embodiment are similar to those in the first embodiment, but the optical data such as the curvature radius, the lens thickness, the aspheric surface or the back focal length in this embodiment are different from the optical data in the first embodiment. Besides, in this embodiment, the first lens element  10  has positive refracting power, the periphery region  17  of the image-side surface  12  facing toward the image side  3  of the first lens element  10  is convex, the periphery region  24  of the object-side surface  21  facing toward the object side  2  of the second lens element  20  is concave, the optical axis region  26  of the image-side surface  22  facing toward the image side  3  of the second lens element  20  is concave and the fourth lens element  40  has negative refracting power. 
     The optical data of the third embodiment of the optical imaging lens are shown in  FIG.  24    while the aspheric surface data are shown in  FIG.  25   . In this embodiment, image height=1.500 mm; EFL=2.554 mm; HFOV=30.000 degrees; TTL=3.743 mm; Fno=1.5. In particular, the imaging quality of the optical imaging lens in this embodiment is better than that of the optical imaging lens in the first embodiment. 
     Fourth Embodiment 
     Please refer to  FIG.  12    which illustrates the fourth embodiment of the optical imaging lens  1  of the present invention. Please refer to  FIG.  13 A  for the longitudinal spherical aberration on the image plane  71  of the fourth embodiment; please refer to  FIG.  13 B  for the field curvature on the sagittal direction; please refer to  FIG.  13 C  for the field curvature on the tangential direction; and please refer to  FIG.  13 D  for the distortion. The components in this embodiment are similar to those in the first embodiment, but the optical data such as the curvature radius, the lens thickness, the aspheric surface or the back focal length in this embodiment are different from the optical data in the first embodiment. Besides, in this embodiment, the first lens element  10  has positive refracting power, the periphery region  37  of the image-side surface  32  facing toward the image side  3  of the third lens element  30  is concave and the fourth lens element  40  has negative refracting power. There is a filter  70  disposed between the fourth lens element  40  and the image plane  71  in the fourth embodiment and the filter  70  may be coated with a film which exclusively allow IR to pass through. 
     The optical data of the fourth embodiment of the optical imaging lens are shown in  FIG.  26    while the aspheric surface data are shown in  FIG.  27   . In this embodiment, image height=1.977 mm; EFL=2.498 mm; HFOV=35.043 degrees; TTL=3.628 mm; Fno=1.29. In particular, 1. the Fno of the optical imaging lens in this embodiment is smaller than that of the optical imaging lens in the first embodiment, 2. the longitudinal spherical aberration of the optical imaging lens in this embodiment is better than that of the optical imaging lens in the first embodiment. 
     Fifth Embodiment 
     Please refer to  FIG.  14    which illustrates the fifth embodiment of the optical imaging lens  1  of the present invention. Please refer to  FIG.  15 A  for the longitudinal spherical aberration on the image plane  71  of the fifth embodiment; please refer to  FIG.  15 B  for the field curvature on the sagittal direction; please refer to  FIG.  15 C  for the field curvature on the tangential direction, and please refer to  FIG.  15 D  for the distortion. The components in this embodiment are similar to those in the first embodiment, but the optical data such as the curvature radius, the lens thickness, the aspheric surface or the back focal length in this embodiment are different from the optical data in the first embodiment. Besides, in this embodiment, the first lens element  10  has positive refracting power, the periphery region  34  of the object-side surface  31  facing toward the object side  2  of the third lens element  30  is convex, the periphery region  37  of the image-side surface  32  facing toward the image side  3  of the third lens element  30  is concave and the fourth lens element  40  has negative refracting power. 
     The optical data of the fifth embodiment of the optical imaging lens are shown in  FIG.  28    while the aspheric surface data are shown in  FIG.  29   . In this embodiment, image height=1.500 mm; EFL=2.170 mm; HFOV=34.255 degrees; TTL=3.900 mm; Fno=1.25. In particular, 1. the Fno of the optical imaging lens in this embodiment is smaller than that of the optical imaging lens in the first embodiment, 2. the longitudinal spherical aberration and the distortion of the optical imaging lens in this embodiment are better than those of the optical imaging lens in the first embodiment. 
     Sixth Embodiment 
     Please refer to  FIG.  16    which illustrates the sixth embodiment of the optical imaging lens  1  of the present invention. Please refer to  FIG.  17 A  for the longitudinal spherical aberration on the image plane  71  of the sixth embodiment; please refer to  FIG.  17 B  for the field curvature on the sagittal direction; please refer to  FIG.  17 C  for the field curvature on the tangential direction, and please refer to  FIG.  17 D  for the distortion. The components in this embodiment are similar to those in the first embodiment, but the optical data such as the curvature radius, the lens thickness, the aspheric surface or the back focal length in this embodiment are different from the optical data in the first embodiment. Besides, in this embodiment, the first lens element  10  has positive refracting power, the periphery region  17  of the image-side surface  12  facing toward the image side  3  of the first lens element  10  is convex, the periphery region  24  of the object-side surface  21  facing toward the object side  2  of the second lens element  20  is concave, the periphery region  37  of the image-side surface  32  facing toward the image side  3  of the third lens element  30  is concave and the fourth lens element  40  has negative refracting power. 
     The optical data of the sixth embodiment of the optical imaging lens are shown in  FIG.  30    while the aspheric surface data are shown in  FIG.  31   . In this embodiment, image height=1.500 mm; EFL=2.134 mm; HFOV=33.397 degrees; TTL=3.318 mm; Fno=1.00. In particular, 1. the Fno of the optical imaging lens in this embodiment is smaller than that of the optical imaging lens in the first embodiment, 2. the distortion of the optical imaging lens in this embodiment is better than that of the optical imaging lens in the first embodiment. 
     Seventh Embodiment 
     Please refer to  FIG.  18    which illustrates the seventh embodiment of the optical imaging lens  1  of the present invention. Please refer to  FIG.  19 A  for the longitudinal spherical aberration on the image plane  71  of the seventh embodiment; please refer to  FIG.  19 B  for the field curvature on the sagittal direction; please refer to  FIG.  19 C  for the field curvature on the tangential direction, and please refer to  FIG.  19 D  for the distortion. The components in this embodiment are similar to those in the first embodiment, but the optical data such as the curvature radius, the lens thickness, the aspheric surface or the back focal length in this embodiment are different from the optical data in the first embodiment. Besides, in this embodiment, the first lens element  10  has positive refracting power, the periphery region  24  of the object-side surface  21  facing toward the object side  2  of the second lens element  20  is concave and the periphery region  34  of the object-side surface  31  facing toward the object side  2  of the third lens element  30  is convex. 
     The optical data of the seventh embodiment of the optical imaging lens are shown in  FIG.  32    while the aspheric surface data are shown in  FIG.  33   . In this embodiment, image height=1.500 mm; EFL=2.162 mm; HFOV=32.555 degrees; TTL=3.545 mm; Fno=0.96. In particular, 1. the Fno of the optical imaging lens in this embodiment is smaller than that of the optical imaging lens in the first embodiment, 2. the imaging quality of the optical imaging lens in this embodiment is better than that of the optical imaging lens in the first embodiment, 3. the fabrication of this embodiment is easier than that of the first embodiment so the yield is better. 
     Some important ratios in each embodiment are shown in  FIG.  34    and in  FIG.  35   . 
     The applicant found that by the following designs matched with each other, the lens configuration in the embodiments of the present invention has the features and corresponding advantages: 
     1. The optical-axis region of the image-side surface of the first lens element is designed to be concave, the periphery region of the image-side surface of the second lens element is convex, the third lens has positive refracting power and the optical-axis region of the object-side surface of the fourth lens element is designed to be convex. It effectively increases the luminous flux of the total optical imaging lens system to simultaneously have good imaging quality. 
     By controlling υ2≤30.000 to go with (1+υ3+υ4)≤120.000, it helps to correct the chromatic aberration of the entire optical system. The selection of the above-mentioned materials facilitates the purpose of the reduction of the length of the optical system due to the higher refractive index. υ2 is preferably 20.000≤υ2≤30.000 and (υ1+υ3+υ4) is preferably 60.000≤(1+υ3+υ4)≤120.000. 
     In addition, it is further discovered that there are some better ratio ranges for different optical data according to the above various important ratios. Better optical ratio ranges help the designers to design a better optical performance and an effectively reduce length of a practically possible optical imaging lens set: 
     To diminish the total length of the optical imaging lens, to ensure good imaging quality and to take the easiness of the fabrication of the optical imaging lens into consideration, the embodiments of the present invention proposes the solution to reduce the lens thickness and air gaps between adjacent lens elements. The following conditions help the optical imaging lens have better arrangement: 
     1) ALT/BFL≥1.200, the preferable range is 1.200≤ALT/BFL≤2.700; 
     2) AAG/G23≤2.200, the preferable range is 1.000≤AAG/G23≤2.200; 
     3) EFL/(T1+T3)≤3.500, the preferable range is 2.000≤EFL/(T1+T3)≤3.500; 
     4) (T2+T3)/T11.800, the preferable range is 1.800≤(T2+T3)/T1≤3.300; 
     5) (T3+T4)/(G23+G34)≤3.500, the preferable range is 0.600≤(T3+T4)/(G23+G34)≤3.500; 
     6) (T1+T2)/(G12+G23)≤2.800, the preferable range is 0.700≤(T1+T2)/(G12+G23)≤2.800; 
     7) BFL/(G34+T4)≤3.100, the preferable range is 1.000≤BFL/(G34+T4)≤3.100; 
     8) TL/(T1+G12)≥3.200, the preferable range is 3.200≤TL/(T1+G12)≤6.800; 
     9) EFL/AAG≤3.900, the preferable range is 1.900≤EFL/AAG≤3.900; 
     10) TTL/(T3+T4)≥3.800, the preferable range is 3.800≤TTL/(T3+T4)≤5.500; 
     11) ALT/T2≤4.800, the preferable range is 2.500≤ALT/T2≤4.800; 
     12) (T4+BFL)/T3≤4.500, the preferable range is 2.500 (T4+BFL)/T3≤4.500; 
     13) T2/T1≥1.000, the preferable range is 1.000≤T2/T1≥2.000; 
     14) ALT/AAG≤4.500, the preferable range is 1.500≤ALT/AAG≤4.500; 
     15) TL/BFL≥1.800, the preferable range is 1.800≤TL/BFL≤3.500; 
     16) (T2+T3+T4)/T1≥2.500, the preferable range is 2.500≤(T2+T3+T4)/T1≥4.500; 
     17) (T1+T3+T4)/T2≤3.500, the preferable range is 1.500≤(T1+T3+T4)/T2≤3.500; 
     18) EFL/(T2+G23)≤3.000, the preferable range is 1.500≤EFL/(T2+G23)≤3.000; 
     19) ALT/T1≥3.500, the preferable range is 3.500≤ALT/T1≤5.500. 
     In the light of the unpredictability of the optical imaging lens, the present invention suggests the above principles to have a shorter total length of the optical imaging lens, a larger aperture available, better imaging quality or a better fabrication yield to overcome the drawbacks of prior art. 
     In addition to the above ratios, one or more conditional formulae may be optionally combined to be used in the embodiments of the present invention and the present invention is not limit to this. The curvatures of each lens element or multiple lens elements may be fine-tuned to result in more fine structures to enhance the performance or the resolution. The above limitations may be properly combined in the embodiments without causing inconsistency. 
     The maximum and minimum numeral values derived from the combinations of the optical parameters disclosed in the embodiments of the invention may all be applicable and enable people skill in the pertinent art to implement the invention. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.