Patent Publication Number: US-2022229270-A1

Title: Large-aperture four-piece optical lens

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims priority to and the benefit of Chinese Patent Application No. CN202110064542.5 filed in China on Jan. 18, 2021. The disclosure of the above application is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present invention relates to an optical lens, and more particularly, to a large-aperture four-piece optical lens. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     In traditional technologies, a headlight lens based on a projection principle is composed of a light source, a light energy collecting member, a cut-off line structure and a convex lens. 
     A light digital projection technology is used in a newly developed pixel headlight which is also known as a matrix headlight, so that the headlight not only has a lighting function, but also can project patterns on the ground, such as weather conditions, road navigation, or other symbols for identification by people outside a vehicle. An optical system of the pixel headlight mainly comprises an illuminable pixel (such as mini LED, micro LED, LCD screen, LCOS or lightened DMD digital microlens) and a projection optical lens. In order to make the projection pattern clearly visible, the lens needs to have a good optical performance: chromatic aberration, field curvature, astigmatism and other optical aberrations are eliminated. 
     For the optical lens in the prior art, a plurality of positive and negative lenses need to be properly combined for joint use, so as to eliminate aberration. A specific number of the optical lenses used is related to parameters, performance indexes, and used optical materials and optical processes of the optical lenses, and a slightly complicated optical lens may be provided with more than 10 lenses. The optical lens currently used in a mobile phone is provided with more than 6 lenses, with a high cost. 
     In traditional technologies, the imaging quality of a Cook&#39;s three-piece lens is difficult to meet requirements.  FIG. 1  shows a classic four-piece three-set Tessar lens, which is evolved from the Cook&#39;s three-piece lens, that is, the last set of single convex lenses is a double-cemented lens. The Tessar lens has sharp imaging and good correction for various aberrations, but a numerical aperture of original design is small, and is generally only about 0.125 and less than 0.2, which means that a utilization rate of light energy is extremely low, and the lenses need to be adjusted very accurately in assembly and use, with small tolerance and high use requirements. A four-piece double Gauss lens also has the above problems. 
     The headlight has both lighting and imaging functions. On one hand, a higher energy utilization rate and a higher brightness are needed, and on the other hand, there are certain image quality requirements for a projected image, especially low chromatic aberration. In addition, due to a particularity of automobile application, the optical lens needs to have a higher thermal reliability, a better vibration reliability and a lower mass, and in order to further improve the market competitiveness, a lower cost is needed at the same time. 
     The optical lens in the prior art cannot meet the performance requirements of a high energy utilization rate, a high imaging quality, a simple and stable structure and a low cost at the same time. 
     SUMMARY 
     Aiming at the problems in the prior art above, the present invention provides a large-aperture four-piece optical lens, which has a high energy utilization rate, a high imaging quality, a simple and stable structure and low manufacturing and using cost. 
     The large-aperture four-piece optical lens provided by the present invention comprises a first lens with positive focal power, a second lens with negative focal power, a third lens with positive focal power and a fourth lens with positive focal power which are sequentially arranged, wherein two surfaces of the first lens are an S1 surface and an S2 surface respectively, two surfaces of the second lens are an S3 surface and an S4 surface respectively, two surfaces of the third lens are an S5 surface and an S6 surface respectively, two surfaces of the fourth lens are an S7 surface and an S8 surface respectively, the S1 surface, the S2 surface, the S3 surface, the S4 surface, the S5 surface, the S6 surface, the S7 surface and the S8 surface are sequentially arranged, a side of the S8 surface far away from the S7 surface is provided with an S9 surface, an aperture diaphragm is arranged on a side of the Si surface or between the S2 surface and the S3 surface, a vignetting diaphragm is arranged on the S7 surface, the S1 surface, the S2 surface, the S5 surface, the S6 surface and the S7 surface are all convex surfaces, and the S4 surface is a concave surface; 
     a distance between the aperture diaphragm and an object focal point of the lens is |ST-F obj |, and an equivalent focal length of the lens is f 0 , |ST−F obj |&lt;0.7f 0 ; 
     an aperture d of the S1 surface to the S8 surface satisfies the following relationship: d i &gt;0.9d j , i&lt;j, i is an integer ranging from 1 to 7, and j is an integer ranging from 2 to 8; 
     a radius of curvature of the S3 surface is r 3 , a radius of curvature of the S4 surface is r 4 , |r 4 |&lt;|r 3 |, a radius of curvature of the S7 surface is r 7 , a radius of curvature of the S8 surface is r 8 , |r 7 |&lt;|r 8 |, an equivalent focal length of the fourth lens is greater than that of the third lens, and the equivalent focal length of the fourth lens is greater than that of the first lens; and 
     a distance between centers of the S6 surface and the S7 surface is G 67 , and a distance between centers of the S2 surface and the S3 surface is G 23 , G 67 &lt;G 23 . 
     Preferably, a rear intercept of the lens is greater than 2 mm. 
     Preferably, the S8 surface is a flat surface or a concave surface. 
     Preferably, the S1 surface, the S2 surface, the S3 surface, the S4 surface, the S5 surface, the S6 surface, the S7 surface and the S8 surface are spherical surfaces or aspherical surfaces. 
     Preferably, the first lens, the second lens, the third lens and the fourth lens are single lenses or cemented lenses. 
     Preferably, the first lens, the second lens, the third lens and the fourth lens are glass lenses or plastic lenses. 
     Further, an Abbe number of the first lens is Vd 1 , an Abbe number of the second lens is Vd 2 , an Abbe number of the third lens is Vd 3 , and an Abbe number of the fourth lens is Vd 4 , Vd 1 −Vd 2 &gt;25, Vd 3 −Vd 2 &gt;25, Vd 4 −Vd 2 &gt;25. 
     The present invention has the beneficial effects that: the present invention discloses the large-aperture four-piece optical lens, only four lenses are used in the lens, with a low manufacturing cost, a simple and stable overall structure, a good anti-vibration performance and a low lens mass, and the lenses have a low sensitivity to axial tolerance in assembly, with a large tolerance rate, a low assembly difficulty and a low assembly cost; and an energy utilization rate can be improved by increasing the numerical aperture, which can effectively improve a brightness of light distribution, and when applied to the projection imaging system, the optical lens has a good chromatic dispersion performance and a good image resolution, which means that the optical lens has a high imaging quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in detail below in conjunction with embodiments and accompanying drawings, in which: 
         FIG. 1  is a schematic structural diagram of a lens system of a Tessar lens. 
         FIG. 2  is a schematic structural diagram of Embodiment 1 of the present invention. 
         FIG. 3  is a graph of an astigmatism and field curvature curve and a distortion curve in Embodiment 1 of the present invention. 
         FIG. 4  is a graph of an on-axis chromatic aberration curve in Embodiment 1 of the present invention. 
         FIG. 5  is a graph of a MTF curve in Embodiment 1 of the present invention. 
         FIG. 6  is a schematic structural diagram of Embodiment 2 of the present invention. 
         FIG. 7  is a graph of an astigmatism and field curvature curve and a distortion curve in Embodiment 2 of the present invention. 
         FIG. 8  is a graph of an on-axis chromatic aberration curve in Embodiment 2 of the present invention. 
         FIG. 9  is a graph of a MTF curve in Embodiment 2 of the present invention. 
     
    
    
     Reference numerals:  10  refers to first lens,  11  refers to S1 surface,  12  refers to S2 surface,  20  refers to second lens,  21  refers to S3 surface,  22  refers to S4 surface,  30  refers to third lens,  31  refers to S5 surface,  32  refers to S6 surface,  40  refers to fourth lens,  41  refers to S7 surface,  42  refers to S8 surface,  50  refers to S9 surface,  60  refers to aperture diaphragm, and  70  refers to vignetting diaphragm. 
     DETAILED DESCRIPTION 
     In order to further understand the features, the technical means, and the achieved specific objectives and functions of the present invention, the present invention is further described in detail hereinafter with reference to the accompanying drawings and the specific embodiments. 
     With reference to  FIG. 1  to  FIG. 9 , 
     a basic embodiment of the present invention discloses a large-aperture four-piece optical lens, which comprises a first lens  10  with positive focal power, a second lens  20  with negative focal power, a third lens  30  with positive focal power and a fourth lens  40  with positive focal power which are sequentially arranged along a light incident direction. Two surfaces of the first lens  10  are an S1 surface  11  and an S2 surface  12  respectively, two surfaces of the second lens  20  are an S3 surface  21  and an S4 surface  22  respectively, two surfaces of the third lens  30  are an S5 surface  31  and an S6 surface  32  respectively, and two surfaces of the fourth lens  40  are an S7 surface  41  and an S8 surface  42  respectively. The S1 surface  11 , the S2 surface  12 , the S3 surface  21 , the S4 surface  22 , the S5 surface  31 , the S6 surface  32 , the S7 surface  41  and the S8 surface  42  are sequentially arranged along a light incident direction. A side of the S8 surface  42  far away from the S7 surface  41  is provided with an S9 surface  50 , and the S9 surface  50  is an image surface, which means that the S 9  surface  50  is located at an image focal point of a whole optical lens. An aperture diaphragm  60  is arranged on a side of the S1 surface  11  or between the S2 surface  12  and the S3 surface  21 . Ideally, the aperture diaphragm  60  is located on a side of the S1 surface  11  far away from the S2 surface  12 . When applied to a vehicle headlight lens, considering a modeling design requirement, the aperture diaphragm  60  may be arranged between the S2 surface  12  and the S3 surface  21 , so that a structural body of the aperture diaphragm  60  can be hidden inside the lens, and the structural body of the aperture diaphragm  60  cannot be observed outside the vehicle headlight lens. A vignetting diaphragm  70  is arranged on the S7 surface  41 , and the vignetting diaphragm  70  is generally a lens mount. The S1 surface  11 , the S2 surface  12 , the S5 surface  31 , the S6 surface  32  and the S7 surface  41  are all convex surfaces, and the S4 surface  22  is a concave surface. 
     A distance between the aperture diaphragm  60  and an object focal point of the whole optical lens is |ST-F obj |, ST represents a distance between the aperture diaphragm  60  and a center of the whole optical lens, and F obj  represents a distance between the object focal point of the whole optical lens and the center of the whole optical lens. An equivalent focal length of the whole optical lens is f 0 , and in practical application, the object focal point of the whole optical lens may be inside the first lens  10 , so that the aperture diaphragm  60  is arranged near the object focal point of the whole optical lens, which means that the following formula: |ST−F obj |&lt;0.7f 0  is satisfied. 
     Apertures d 1 ˜d 8  of the S1 surface  11  to the S8 surface  42  satisfy the following relationship: d i &gt;0.9d j , i&lt;j, i is an integer ranging from 1 to 7, j is an integer ranging from 2 to 8, and d is an aperture of a corresponding optical surface. Along a light incident direction, the apertures of the S1 surface  11  to the S8 surface  42  are changed basically conforming to a trend of gradual decrease. 
     A radius of curvature of the S3 surface  21  is r 3 , a radius of curvature of the S 4  surface  22  is r 4 , |r 4 |&lt;|r 3 |, and a radius of curvature of the S7 surface  41  is r 7 , a radius of curvature of the S8 surface  42  is r 8 , |r 7 |&lt;|r 8 |. An equivalent focal length of the fourth lens  40  is greater than that of the third lens  30 , that is, f 4 &gt;f 3 , and the equivalent focal length of the fourth lens  40  is greater than that of the first lens  10 , that is, f 4 &gt;f 1 . 
     A distance between centers of the S6 surface  32  and the S7 surface  41  is G 67 , and a distance between centers of the S2 surface  12  and the S3 surface  21  is G 23 , G 67 &lt;G 23 . 
     In operation, a ray sequentially reaches the S1 surface  11 , the S2 surface  12 , the S3 surface  21 , the S4 surface  22 , the S5 surface  31 , the S6 surface  32 , the S7 surface  41 , the S8 surface  42  and the S9 surface  50 . The optical lens of the present invention can significantly improve a chromatic dispersion performance of a vehicle headlight, and reduce a sensitivity of the lens to axial tolerance in assembly, with a high assembly tolerance rate and a low assembly difficulty. 
     For a Tessar lens based on a classic Cook&#39;s three-piece variant, as shown in  FIG. 1 , the aperture diaphragm is generally arranged at a middle lens, which can reduce or correct common aberration, such as field curvature, astigmatism and chromatic aberration, through structural symmetry. However, this structure, on one hand, may lead to a small numerical aperture for describing an overall light energy utilization rate; and on the other hand, may also lead to a very large chief ray angle CRA of a chief ray of a large field of view on an image surface. An illumination intensity of a general light source satisfies a Lambert&#39;s cosine law, and the illumination intensity is maximum at a 0-degree position, decays to 0.5 at a 60-degree position, and is 0 at a 90-degree position. Due to a large chief ray angle CRA, it is indicated that energy obtained by the lens system is lower for a solid angle of the same size. 
     According to the present invention, the aperture diaphragm  60  is arranged at the object focal point of the optical lens, thus forming an image space telecentric lens, so that the chief rays of the fields of view are parallel, that is, the chief ray angles CRA of the chief rays of the fields of view on the image surface which is namely the S9 surface  50  are all 0 degree, which means that the energy utilization rate of the present invention is higher for the solid angle of the same size. In practical application, the aperture diaphragm  60  is arranged near the object focal point of the optical lens, and the chief ray angles of the chief rays of the fields of view on the image surface which is namely the S9 surface  50  are all less than 20 degrees, with a high energy utilization rate. 
     In the embodiment, a rear intercept of the lens is greater than 2 mm, which means that a distance between the S8 surface  42  and the S9 surface  50  is greater than 2 mm. Since the light source may generate a certain amount of heat in use, the four-piece optical lens provided with sufficient rear intercept can effectively avoid deformation of parts caused by heating. 
     In the embodiment, the S8 surface  42  is a flat surface or a concave surface. In the embodiment, the S1 surface  11 , the S2 surface  12 , the S3 surface  21 , the S4 surface  22 , the S5 surface  31 , the S6 surface  32 , the S7 surface  41  and the S8 surface  42  are spherical surfaces or aspherical surfaces, which means that the S1 surface  11  to the S8 surface  42  may all be spherical surfaces, or the S1 surface  11  to the S8 surface  42  may all be aspherical surfaces, or the S1 surface  11  to the S8 surface  42  comprise spherical surfaces and aspherical surfaces. The aspherical surface is a rationally designed surface type. 
     In the embodiment, the first lens  10 , the second lens  20 , the third lens  30  and the fourth lens  40  are single lenses or cemented lenses, which means that the first lens  10 , the second lens  20 , the third lens  30  and the fourth lens  40  may all be single lenses, or the first lens  10 , the second lens  20 , the third lens  30  and the fourth lens  40  may all be cemented lenses, or the first lens  10 , the second lens  20 , the third lens  30  and the fourth lens  40  comprise single lenses and cemented lenses. The cemented lens, also known as an achromatic lens, is formed by cementing two single lenses, and a multi-color imaging performance of the cemented lens is much better than that of the single lens. 
     In the embodiment, the first lens  10 , the second lens  20 , the third lens  30  and the fourth lens  40  are glass lenses or plastic lenses, which means that the first lens  10 , the second lens  20 , the third lens  30  and the fourth lens  40  may all be glass lenses, or the first lens  10 , the second lens  20 , the third lens  30  and the fourth lens  40  may all be plastic lenses, or the first lens  10 , the second lens  20 , the third lens  30  and the fourth lens  40  comprise glass lenses and plastic lenses. 
     In the embodiment, an Abbe number of the first lens  10  is Vd 1 , an Abbe number of the second lens  20  is Vd 2 , an Abbe number of the third lens  30  is Vd 3 , and an Abbe number of the fourth lens  40  is Vd 4 , Vd 1 −Vd 2 &gt;25, Vd 3 −Vd 2 &gt;25, Vd 4 −Vd 2 &gt;25. 
     In Embodiment 1, a structure of an optical lens is shown in  FIG. 2 , and the optical lens is arranged according to Table 1, Table 2, Table 3 and Table 4 below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Parameters of surfaces in Embodiment 1 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Serial No. 
                 Type of 
                 Radius of curvature 
                 Thickness 
                 Refractive 
                 Abbe number 
                 Aperture 
               
               
                 of surface 
                 surface 
                 r (mm) 
                 (mm) 
                 index n 
                 Vd 
                 d 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Object 
                 Spherical 
                 Infinity 
                 25,000 
                   
                   
                   
               
               
                 surface 
                 surface 
                   
                   
                   
                   
                   
               
               
                 Aperture 
                 Spherical 
                 Infinity 
                 0.00 
                   
                   
                 41.88 
               
               
                 diaphragm 
                 surface 
                   
                   
                   
                   
                   
               
               
                 S1 
                 Aspherical 
                 46.83 
                 15.42 
                 1.492 
                 57.98 
                 41.89 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S2 
                 Aspherical 
                 −10.40 
                 4.50 
                   
                   
                 41.08 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S3 
                 Aspherical 
                 20.42 
                 2.43 
                 1.584 
                 27.86 
                 30.35 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S4 
                 Aspherical 
                 4.62 
                 6.56 
                   
                   
                 25.75 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S5 
                 Spherical 
                 20.99 
                 13.80 
                 1.487 
                 70.42 
                 26.50 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S6 
                 Spherical 
                 −30.17 
                 0.09 
                   
                   
                 25.59 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S7 
                 Spherical 
                 17.96 
                 11.24 
                 1.755 
                 52.30 
                 20.65 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S8 
                 Spherical 
                 54.09 
                 4.31 
                   
                   
                 14.42 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S9 
                 Spherical 
                 Infinity 
                 0.00 
                   
                   
                 10.00 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     An expression of the aspherical surface is as follows: 
     
       
         
           
             z 
             = 
             
               
                 
                   c 
                   ⁢ 
                   
                     r 
                     2 
                   
                 
                 
                   1 
                   + 
                   
                     
                       1 
                       - 
                       
                         
                           ( 
                           
                             1 
                             + 
                             k 
                           
                           ) 
                         
                         ⁢ 
                         
                           c 
                           2 
                         
                         ⁢ 
                         
                           r 
                           2 
                         
                       
                     
                   
                 
               
               + 
               
                 A 
                 ⁢ 
                 
                   r 
                   4 
                 
               
               + 
               
                 B 
                 ⁢ 
                 
                   r 
                   6 
                 
               
               + 
               
                 C 
                 ⁢ 
                 
                   r 
                   8 
                 
               
               + 
               
                 D 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     0 
                   
                 
               
               + 
               
                 E 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     2 
                   
                 
               
               + 
               
                 F 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     4 
                   
                 
               
               + 
               
                 G 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     6 
                   
                 
               
               + 
               
                 H 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     8 
                   
                 
               
               + 
               
                 Jr 
                 
                   2 
                   ⁢ 
                   0 
                 
               
             
           
         
       
     
     wherein z is a vector height of an r position on the aspherical surface, c is a paraxial curvature of the aspherical surface, c=1/r, r is a radius of curvature, k is a conic coefficient, and A to J are higher-order coefficients. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Parameters of aspherical surfaces in Embodiment 1 
               
            
           
           
               
               
               
               
               
            
               
                   
                 S1 
                 S2 
                 S3 
                 S4 
               
               
                   
               
               
                 Conic coefficient k 
                 0 
                 −4.932 
                 −8.84E−01 
                 −1.77E+00 
               
               
                 A 
                 −1.90E−05 
                   1.10E−05 
                 −1.07E−04 
                   5.28E−06 
               
               
                 B 
                   9.32E−08 
                 −4.95E−08 
                   3.52E−07 
                   1.25E−07 
               
               
                 C 
                 −3.69E−10 
                   6.47E−11 
                 −6.71E−10 
                 −6.40E−10 
               
               
                 D 
                   6.38E−13 
                   4.00E−16 
                   3.73E−13 
                   8.26E−13 
               
               
                 E 
                 −3.68E−16 
                 0 
                 0 
                 0 
               
            
           
           
               
            
               
                 Other higher-order coefficients are all 0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
               
                   
               
             
            
               
                 Design parameters of optical lenses in Embodiment 1 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 Equivalent focal 
                 f1 1   
                 f1 2   
                 f1 3   
                 f1 4   
                 Rear 
                   
                 Numerical 
                 1/2 FOV 
               
               
                 Parameter 
                 length f 0  (mm) 
                 (mm) 
                 (mm) 
                 (mm) 
                 (mm) 
                 intercept 
                 f/EPD 
                 aperture NA 
                 (°) 
               
               
                   
               
               
                 Value 
                 28.3 
                 19.00 
                 −10.81 
                 27.85 
                 31.41 
                 4.30 
                 0.67 
                 0.74 
                 10.0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Constrained relationships in Embodiment 1 
               
            
           
           
               
               
            
               
                 Constrained relationship 
                 Result 
               
               
                   
               
               
                 |ST − F obj | &lt; 0.7f 0   
                 |ST − F obj | = 12.81 mm, so that the condition is satisfied 
               
               
                 Aperture d i  &gt; 0.9d j   
                 It can be seen from Table 1 that the condition is satisfied 
               
               
                 The S7 surface is provided  
                 A vignetting coefficient of ½ FOV is 0.45 
               
               
                 with the vignetting diaphragm 
                   
               
               
                 |r 4 | &lt; |r 3 | 
                 It can be seen from Table 1 that the condition is satisfied 
               
               
                 r 4  &lt; 0 
                 It can be seen from Table 1 that the condition is satisfied 
               
               
                 f 4  &gt; f 3   
                 It can be seen from Table 3 that the condition is satisfied 
               
               
                 f 4  &gt; f 1   
                 It can be seen from Table 3 that the condition is satisfied 
               
               
                 |r 7 | &lt; |r 8 | 
                 It can be seen from Table 1 that the condition is satisfied 
               
               
                 G 67  &lt; G 23   
                 It can be seen from Table 1 that the condition is satisfied 
               
               
                 The rear intercept is greater  
                 It can be seen from Table 3 that the rear intercept is 4.3  
               
               
                 than 2 mm 
                 mm, and the condition is satisfied 
               
               
                   
               
            
           
         
       
     
     To sum up, it can be seen that the numerical aperture in Embodiment 1 reaches 0.74, which is much greater than 0.125 of the Tessar lens, so that the energy utilization rate is significantly improved. An astigmatism and field curvature curve and a distortion curve in Embodiment 1 are shown in  FIG. 3 , an on-axis chromatic aberration curve is shown in  FIG. 4 , and a MTF (Modulation Transfer Function) curve is shown in  FIG. 5 . It can be seen that the optical lens has a good imaging quality when applied to a projection imaging system. 
     In Embodiment 2, a structure of an optical lens is shown in  FIG. 6 , and the optical lens is arranged according to Table 5, Table 6, Table 7 and Table 8 below. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Parameters of surfaces in Embodiment 2 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Serial No. of 
                 Type of 
                 Radius of 
                 Thickness 
                 Refractive 
                 Abbe 
                   
               
               
                 surface 
                 surface 
                 curvature r (mm) 
                 (mm) 
                 index n 
                 number Vd 
                 Aperture d 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Object 
                 Spherical 
                 Infinity 
                 25000 
                   
                   
                   
               
               
                 surface 
                 surface 
                   
                   
                   
                   
                   
               
               
                 S1 
                 Aspherical 
                 42.622 
                 8.510 
                 1.492 
                 57.98 
                 28.93 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S2 
                 Aspherical 
                 −12.870 
                 7.441 
                   
                   
                 28.16 
               
               
                 (aperture 
                 surface 
                   
                   
                   
                   
                   
               
               
                 diaphragm) 
                   
                   
                   
                   
                   
                   
               
               
                 S3 
                 Aspherical 
                 −115.860 
                 2.390 
                 1.584 
                 27.86 
                 20.16 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S4 
                 Aspherical 
                 4.641 
                 2.626 
                   
                   
                 18.30 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S5 
                 Aspherical 
                 7.185 
                 9.354 
                 1.586 
                 60.60 
                 19.07 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S6 
                 Aspherical 
                 −22.594 
                 1.789 
                   
                   
                 17.65 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S7 
                 Spherical 
                 11.890 
                 5.613 
                 1.755 
                 52.30 
                 12.47 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S8 
                 Spherical 
                 20.294 
                 3.115 
                   
                   
                  9.74 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                 S9 
                 Spherical 
                 Infinity 
                 0.00 
                   
                   
                  7.99 
               
               
                   
                 surface 
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     An expression of the aspherical surface is as follows: 
     
       
         
           
             z 
             = 
             
               
                 
                   c 
                   ⁢ 
                   
                     r 
                     2 
                   
                 
                 
                   1 
                   + 
                   
                     
                       1 
                       - 
                       
                         
                           ( 
                           
                             1 
                             + 
                             k 
                           
                           ) 
                         
                         ⁢ 
                         
                           c 
                           2 
                         
                         ⁢ 
                         
                           r 
                           2 
                         
                       
                     
                   
                 
               
               + 
               
                 A 
                 ⁢ 
                 
                   r 
                   4 
                 
               
               + 
               
                 B 
                 ⁢ 
                 
                   r 
                   6 
                 
               
               + 
               
                 C 
                 ⁢ 
                 
                   r 
                   8 
                 
               
               + 
               
                 D 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     0 
                   
                 
               
               + 
               
                 E 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     2 
                   
                 
               
               + 
               
                 F 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     4 
                   
                 
               
               + 
               
                 G 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     6 
                   
                 
               
               + 
               
                 H 
                 ⁢ 
                 
                   r 
                   
                     1 
                     ⁢ 
                     8 
                   
                 
               
               + 
               
                 Jr 
                 
                   2 
                   ⁢ 
                   0 
                 
               
             
           
         
       
     
     wherein z is a vector height of an r position on the aspherical surface, c is a paraxial curvature of the aspherical surface, c=1/r, r is a radius of curvature, k is a conic coefficient, and A to J are higher-order coefficients. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Parameters of aspherical surfaces in Embodiment 2 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 S1 
                 S2 
                 S3 
                 S4 
                 S5 
                 S6 
               
               
                   
               
               
                 Conic 
                 −7.17110872 
                 −5.588 
                   9.36E+00 
                 −2.54E+00 
                 −2.88 
                 −25.40 
               
               
                 coefficient k 
                   
                   
                   
                   
                   
                   
               
               
                 A 
                   3.56E−06 
                   2.36E−06 
                   7.44E−05 
                   8.32E−05 
                   6.35E−05 
                 −2.22E−04 
               
               
                 B 
                 −8.65E−08 
                 −2.25E−08 
                 −1.42E−06 
                   5.47E−07 
                   1.04E−06 
                   3.70E−06 
               
               
                 C 
                   2.83E−10 
                 −8.74E−11 
                   1.14E−08 
                 −4.13E−08 
                 −8.28E−09 
                 −1.79E−08 
               
               
                 D 
                 −6.66E−13 
                   2.12E−13 
                 −1.02E−10 
                   2.43E−10 
                     0E+00 
                   0.00E+00 
               
               
                 E 
                   0.00E+00 
                     0E+00 
                   4.73E−13 
                     0E+00 
                     0E+00 
                     0E+00 
               
            
           
           
               
            
               
                 Other higher-order coefficients are all 0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
               
                   
               
             
            
               
                 Design parameters of optical lenses in Embodiment 2 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 Equivalent focal 
                 f1 1   
                 f1 2   
                 f1 3   
                 f1 4   
                 Rear 
                   
                 Numerical 
                 1/2 FOV 
               
               
                 Parameter 
                 length f 0  (mm) 
                 (mm) 
                 (mm) 
                 (mm) 
                 (mm) 
                 intercept 
                 f/EPD 
                 aperture NA 
                 (°) 
               
               
                   
               
               
                 Value 
                 18.89 
                 21.10 
                 −7.51 
                 10.49 
                 29.41 
                 3.12 
                 0.67 
                 0.75 
                 12.0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Constrained relationships in Embodiment 2 
               
            
           
           
               
               
            
               
                 Constrained relationship 
                 Result 
               
               
                   
               
               
                 |ST − F obj | &lt; 0.7f 0   
                 |ST − F obj | = 6.62 mm, so that the condition is satisfied 
               
               
                 Aperture d i  &gt; 0.9d j   
                 It can be seen from Table 5 that the condition is satisfied 
               
               
                 The S7 surface is provided 
                 A vignetting coefficient of ½ FOV is 0.72 
               
               
                 with the vignetting diaphragm 
                   
               
               
                 |r 4 | &lt; |r 3 | 
                 It can be seen from Table 5 that the condition is satisfied 
               
               
                 r 4  &lt; 0 
                 It can be seen from Table 5 that the condition is satisfied 
               
               
                 f 4  &gt; f 3   
                 It can be seen from Table 7 that the condition is satisfied 
               
               
                 f 4  &gt; f 1   
                 It can be seen from Table 7 that the condition is satisfied 
               
               
                 |r 7 | &lt; |r 8 | 
                 It can be seen from Table 5 that the condition is satisfied 
               
               
                 G 67  &lt; G 23   
                 It can be seen from Table 5 that the condition is satisfied 
               
               
                 The rear intercept is greater 
                 It can be seen from Table 7 that the rear intercept is 3.12  
               
               
                 than 2 mm 
                 mm, and the condition is satisfied 
               
               
                   
               
            
           
         
       
     
     To sum up, it can be seen that the numerical aperture in Embodiment 2 reaches 0.75, which is much greater than 0.125 of the Tessar lens, so that the energy utilization rate is significantly improved. An astigmatism and field curvature curve and a distortion curve in Embodiment 2 are shown in  FIG. 7 , an on-axis chromatic aberration curve is shown in  FIG. 8 , and a MTF (Modulation Transfer Function) curve is shown in  FIG. 9 . It can be seen that the optical lens has a good imaging quality when applied to a projection imaging system. 
     The above embodiments only express some implementation modes of the present invention, and the descriptions thereof are specific and detailed, but cannot be understood as limiting the scope of the patent of the present invention. It shall be pointed out that those of ordinary skills in the art may further make several modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be subject to the appended claims.