Patent Publication Number: US-2021181467-A1

Title: Three-piece infrared single wavelength lens system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/233,022, which claims the earlier filing date of Dec. 26, 2018, the entire specification of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a lens system, and more particularly to a miniaturized three-piece infrared single wavelength lens system applicable to electronic products. 
     Description of the Prior Art 
     Nowadays digital imaging technology is constantly innovating and changing, in particular, digital carriers, such as, digital camera and mobile phone and so on, have become smaller in size, so CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor is also required to be more compact. In addition to be used in the field of photography, in recent years, infrared focusing lens has also be used in infrared receiving and sensing field of the game machine, and in order to make the scope of game machine induction user more broader, wide-angle lens group has become the mainstream for receiving infrared wavelength at present. 
     The applicant has also put forward a number of lens groups related to infrared wavelength reception, however, at present, the game machine is based on a more three-dimensional, real and immediate 3D game, the current or the applicant&#39;s previous lens groups are all 2D plane games, which cannot meet the 3D game focusing on the deep induction efficacy. 
     Special infrared receiving and induction lens groups for game machines are made of plastic for the pursuit of low cost, however, poor material transparency is one of the key factors that affect the depth detection accuracy of the game machine, and plastic lenses are easy to overheat or too cold in ambient temperature, so that the focal length of the lens group will be changed and cannot focus accurately. Therefore, the current infrared receiving and induction lens groups cannot meet the 3D game depth precise induction requirement. 
     The present invention mitigates and/or obviates the aforementioned disadvantages. 
     SUMMARY 
     The primary objective of the present invention is to provide a three-piece infrared single wavelength lens system which has a wide field of view, large stop, short length and less distortion. 
     Therefore, a three-piece infrared single wavelength lens system in accordance with the present invention comprises, in order from an object side to an image side: a first lens element with a negative refractive power having an object-side surface being convex near an optical axis and an image-side surface being concave near the optical axis, at least one of the object-side surface and the image-side surface of the first lens element being aspheric; a stop; a second lens element with a positive refractive power having an image-side surface being convex near the optical axis, at least one of an object-side surface and the image-side surface of the second lens element being aspheric; and a third lens element with a refractive power having an object-side surface being convex near the optical axis and an image-side surface being concave near the optical axis, at least one of the object-side surface and the image-side surface of the third lens element being aspheric. 
     Preferably, a focal length of the three-piece infrared single wavelength lens system is f, a focal length of the first lens element and the second lens element combined is f12, and they satisfy the relation: 0.5&lt;f/f12&lt;1.1, so that the shortening of the total length of the system and the correction of aberration can be balanced. 
     Preferably, the focal length of the three-piece infrared single wavelength lens system is f, a focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.8&lt;f/f23&lt;1.6, so that the shortening of the total length of the system and the correction of aberration can be balanced. 
     Preferably, a focal length of the first lens element is f1, a focal length of the second lens element is f2, and they satisfy the relation: −19&lt;f1/f2&lt;−1.4. Therefore, the refractive powers of the first and second lens elements can be properly distributed, so that the aberration of the three-piece infrared single wavelength lens system will not be too large. 
     Preferably, the focal length of the second lens element is f2, a focal length of the third lens element is f3, and they satisfy the relation: −0.02&lt;f2/f3&lt;0.26, so that the total optical length of the system can be reduced effectively. 
     Preferably, the focal length of the first lens element is f1, the focal length of the third lens element is f3, and they satisfy the relation: −1.5&lt;f1/f3&lt;0.07, it will be favorable to reduce the sensitivity and the aberration of the system. 
     Preferably, the focal length of the first lens element is f1, the focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: −23&lt;f1/f23&lt;−1.9, so that the resolution can be improved evidently. 
     Preferably, the focal length of the first lens element and the second lens element combined is f12, the focal length of the third lens element is f3, and they satisfy the relation: −0.05&lt;f12/f3&lt;0.37, so that the resolution can be improved evidently. 
     Preferably, a radius of curvature of the image-side surface of the first lens element is R1, a radius of curvature of the image source-side surface of the first lens element is R2, and they satisfy the relation: 0.9&lt;R1/R2&lt;5.3, which can provide good field of view and reduce the high order aberrations of the system. 
     Preferably, a radius of curvature of the image-side surface of the second lens element is R3, a radius of curvature of the image source-side surface of the second lens element is R4, and they satisfy the relation: −27&lt;R3/R4&lt;27, so that the astigmatism of the three-piece infrared single wavelength lens system can be reduced. 
     Preferably, a radius of curvature of the image-side surface of the third lens element is R5, a radius of curvature of the image source-side surface of the third lens element is R6, and they satisfy the relation: 0.7&lt;R5/R6&lt;1.5, so that the curvature configuration of the surfaces of the third lens element can be balanced effectively, so as to balance the field of view with the total track length. 
     Preferably, a central thickness of the first lens element along the optical axis is CT1, a central thickness of the second lens element along the optical axis is CT2, and they satisfy the relation: 0.5&lt;CT1/CT2&lt;1.1, so that the thicknesses of the first and second lens elements are more suitable, it is favorable to the homogeneity and formation of lens elements in manufacture. 
     Preferably, the central thickness of the second lens element along the optical axis is CT2, a central thickness of the third lens element along the optical axis is CT3, and they satisfy the relation: 0.9&lt;CT2/CT3&lt;2.4, so that the thicknesses of the second and third lens elements are more suitable, it is favorable to the homogeneity and formation of lens elements in manufacture. 
     Preferably, the central thickness of the first lens element along the optical axis is CT1, the central thickness of the third lens element along the optical axis is CT3, and they satisfy the relation: 0.6&lt;CT1/CT3&lt;1.8, so that the thicknesses of the first and third lens elements are more suitable, it is favorable to the homogeneity and formation of lens elements in manufacture. 
     Preferably, the focal length of the three-piece infrared single wavelength lens system is f, a distance from the image-side surface of the first lens element to the image source-side surface along the optical axis is TL, and they satisfy the relation: 0.3&lt;f/TL&lt;0.6, it will be favorable to maintain the objective of miniaturization and long focus of the three-piece infrared single wavelength lens system, which can be used in thin electronic products. 
     The present invention will be presented in further details from the following descriptions with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiments in accordance with the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a three-piece infrared single wavelength lens system in accordance with a first embodiment of the present invention; 
         FIG. 1B  shows the image plane curve and the distortion curve of the first embodiment of the present invention; 
         FIG. 2A  shows a three-piece infrared single wavelength lens system in accordance with a second embodiment of the present invention; 
         FIG. 2B  shows the image plane curve and the distortion curve of the second embodiment of the present invention; 
         FIG. 3A  shows a three-piece infrared single wavelength lens system in accordance with a third embodiment of the present invention; 
         FIG. 3B  shows the image plane curve and the distortion curve of the third embodiment of the present invention; 
         FIG. 4A  shows a three-piece infrared single wavelength lens system in accordance with a fourth embodiment of the present invention; 
         FIG. 4B  shows the image plane curve and the distortion curve of the fourth embodiment of the present invention; 
         FIG. 5A  shows a three-piece infrared single wavelength lens system in accordance with a fifth embodiment of the present invention; 
         FIG. 5B  shows the image plane curve and the distortion curve of the fifth embodiment of the present invention; 
         FIG. 6A  shows a three-piece infrared single wavelength lens system in accordance with a sixth embodiment of the present invention; 
         FIG. 6B  shows the image plane curve and the distortion curve of the sixth embodiment of the present invention; 
         FIG. 7A  shows a three-piece infrared single wavelength lens system in accordance with a seventh embodiment of the present invention; and 
         FIG. 7B  shows the image plane curve and the distortion curve of the seventh embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1A and 1B ,  FIG. 1A  shows a three-piece infrared single wavelength lens system in accordance with a first embodiment of the present invention, and  FIG. 1B  shows, in order from left to right, the image plane curve and the distortion curve of the first embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the first embodiment of the present invention comprises a stop  100  and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element  110 , a second lens element  120 , a third lens element  130 , an IR cut filter  170 , and an image plane  180 , wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop  100  is disposed between the first lens element  110  and the second lens element  120 . 
     The first lens element  110  with a negative refractive power has an object-side surface  111  being convex near an optical axis  190  and an image-side surface  112  being concave near the optical axis  190 , the object-side surface  111  and the image-side surface  112  are aspheric, and the first lens element  110  is made of plastic material. 
     The second lens element  120  with a positive refractive power has an object-side surface  121  being concave near the optical axis  190  and an image-side surface  122  being convex near the optical axis  190 , the object-side surface  121  and the image-side surface  122  are aspheric, and the second lens element  120  is made of plastic material. 
     The third lens element  130  with a positive refractive power has an object-side surface  131  being convex near the optical axis  190  and an image-side surface  132  being concave near the optical axis  190 , the object-side surface  131  and the image-side surface  132  are aspheric, the third lens element  130  is made of plastic material, and at least one of the object-side surface  131  and the image-side surface  132  is provided with at least one inflection point. 
     The IR cut filter  170  made of glass is located between the third lens element  130  and the image plane  180  and has no influence on the focal length of the three-piece infrared single wavelength lens system. 
     The equation for the aspheric surface profiles of the respective lens elements of the first embodiment is expressed as follows: 
     
       
         
           
             z 
             = 
             
               
                 
                   ch 
                   2 
                 
                 
                   1 
                   + 
                   
                     
                       [ 
                       
                         1 
                         - 
                         
                           
                             ( 
                             
                               k 
                               + 
                               1 
                             
                             ) 
                           
                            
                           
                             c 
                             2 
                           
                            
                           
                             h 
                             2 
                           
                         
                       
                       ] 
                     
                     0.5 
                   
                 
               
               + 
               
                 Ah 
                 4 
               
               + 
               
                 Bh 
                 6 
               
               + 
               
                 Ch 
                 8 
               
               + 
               
                 Dh 
                 
                   1 
                    
                   0 
                 
               
               + 
               
                 Eh 
                 
                   1 
                    
                   2 
                 
               
               + 
               
                 Fh 
                 
                   1 
                    
                   4 
                 
               
               + 
               
                 
                   Gh 
                   16 
                 
                  
                 
                     
                 
                  
                 … 
               
             
           
         
       
     
     wherein: 
     z represents the value of a reference position with respect to a vertex of the surface of a lens and a position with a height h along the optical axis  190 ; 
     c represents a paraxial curvature equal to 1/R (R: a paraxial radius of curvature); 
     h represents a vertical distance from the point on the curve of the aspheric surface to the optical axis  190 ; 
     k represents the conic constant; 
     A, B, C, D, E, F, G, . . . : represent the high-order aspheric coefficients. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, a focal length of the three-piece infrared single wavelength lens system is f, a f-number of the three-piece infrared single wavelength lens system is Fno, the three-piece infrared single wavelength lens system has a maximum view angle (field of view) FOV, and they satisfy the relations: f=1.46 mm; Fno=2.0; and FOV=77.99 degrees. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the three-piece infrared single wavelength lens system is f, a focal length of the first lens element  110  and the second lens element  120  combined is f12, and they satisfy the relation: f/f12=0.76. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the three-piece infrared single wavelength lens system is f, a focal length of the second lens element  120  and the third lens element  130  combined is f23, and they satisfy the relation: f/f23=1.29. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, a focal length of the first lens element  110  is f1, a focal length of the second lens element  120  is f2, and they satisfy the relation: f1/f2=−2.18. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the second lens element  120  is f2, a focal length of the third lens element  130  is f3, and they satisfy the relation: f2/f3=0.11. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the first lens element  110  is f1, the focal length of the third lens element  130  is f3, and they satisfy the relation: f1/f3=−0.23. In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the first lens element  110  is f1, the focal length of the second lens element  120  and the third lens element  130  combined is f23, and they satisfy the relation: f1/f23=−2.73. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the first lens element  110  and the second lens element  120  combined is f12, the focal length of the third lens element  130  is f3, and they satisfy the relation: f12/f3=0.14. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, the focal length of the three-piece infrared single wavelength lens system is f, a distance from the object-side surface  111  of the first lens element  110  to the image plane  180  along the optical axis  190  is TL, and they satisfy the relation: f/TL=0.39. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, a radius of curvature of the image-side surface  111  of the first lens element  110  is R1, a radius of curvature of the image source-side surface  112  of the first lens element  110  is R2, and they satisfy the relation: R1/R2=2.53. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, a radius of curvature of the image-side surface  121  of the second lens element  120  is R3, a radius of curvature of the image source-side surface  122  of the second lens element  120  is R4, and they satisfy the relation: R3/R4=21.37. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, a radius of curvature of the image-side surface  131  of the third lens element  130  is R5, a radius of curvature of the image source-side surface  132  of the third lens element  130  is R6, and they satisfy the relation: R5/R6=0.99. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, a central thickness of the first lens element  110  along the optical axis  190  is CT1, a central thickness of the second lens element  120  along the optical axis  190  is CT2, and they satisfy the relation: CT1/CT2=0.84. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, the central thickness of the second lens element  120  along the optical axis  190  is CT2, a central thickness of the third lens element  130  along the optical axis  190  is CT3, and they satisfy the relation: CT2/CT3=1.40. 
     In the first embodiment of the present three-piece infrared single wavelength lens system, the central thickness of the first lens element  110  along the optical axis  190  is CT1, the central thickness of the third lens element  130  along the optical axis  190  is CT3, and they satisfy the relation: CT1/CT3=1.17. 
     The detailed optical data of the first embodiment is shown in table 1, and the aspheric surface data is shown in table 2. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Embodiment 1 
               
               
                 f(focal length) = 1.46 mm, Fno = 2.0, FOV = 77.99 deg. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                 Focal 
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 0 
                 object 
                 infinity 
                 400 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 2 
                 Lens 1 
                 2.471 
                 (ASP) 
                 0.627 
                 plastic 
                 1.64 
                 22.46 
                 −3.10 
               
               
                 3 
                   
                 0.977 
                 (ASP) 
                 0.265 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 4 
                 stop 
                 infinity 
                 0.175 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 Lens 2 
                 −18.292 
                 (ASP) 
                 0.748 
                 plastic 
                 1.64 
                 22.46 
                 1.42 
               
               
                 6 
                   
                 −0.856 
                 (ASP) 
                 0.089 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 1.347 
                 (ASP) 
                 0.535 
                 plastic 
                 1.64 
                 22.46 
                 13.54 
               
               
                 8 
                   
                 1.360 
                 (ASP) 
                 0.532 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 9 
                 IR-filter 
                 infinity 
                 0.300 
                 glass 
                 1.517 
                 64.17 
                   
               
               
                 10 
                   
                 infinity 
                 0.487 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 — 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
            
               
                   
               
               
                     2 
               
               
                 Aspheric Coefficients 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 surface 
                 2 
                 3 
                 5 
                 6 
                 7 
                 8 
               
               
                   
               
               
                 K: 
                 −1.0327E+01 
                  3.0863E+00 
                  1.0000E+02 
                 −5.8755E+00 
                 −3.1425E+00 
                  5.0181E−01 
               
               
                 A: 
                  3.1022E−01 
                  9.6810E−01 
                  1.2756E−02 
                 −1.3466E+00 
                 −6.3764E−02 
                  1.9540E−01 
               
               
                 B: 
                 −3.1197E−02 
                 −1.5244E+00 
                  1.1466E+00 
                  2.6519E+00 
                 −2.3095E−01 
                 −9.8564E−01 
               
               
                 C: 
                 −7.6936E−01 
                  1.5958E+01 
                 −1.3834E+01 
                 −5.7362E+00 
                  7.8978E−01 
                  1.4447E+00 
               
               
                 D: 
                  3.6174E+00 
                  7.9098E+00 
                  9.0565E+01 
                  7.7256E+00 
                 −8.0977E−01 
                 −1.2454E+00 
               
               
                 E: 
                 −7.0575E+00 
                  2.7563E+02 
                 −2.6962E+02 
                  1.7481E+00 
                 −2.0375E+00 
                  2.2039E−02 
               
               
                 F 
                  6.7217E+00 
                 −4.2786E+03 
                  4.0275E+02 
                 −2.6779E+01 
                  5.0798E+00 
                  8.3253E−01 
               
               
                 G 
                 −2.4889E+00 
                  2.1456E+04 
                 −2.5241E+02 
                  3.3857E+01 
                 −2.9953E+00 
                 −4.7259E−01 
               
               
                   
               
            
           
         
       
     
     The units of the radius of curvature, the thickness and the focal length in table 1 are expressed in mm, the surface numbers 0-11 represent the surfaces sequentially arranged from the object-side to the image-side along the optical axis. In table 2, k represents the conic coefficient of the equation of the aspheric surface profiles, and A, B, C, D, E, F, G . . . : represent the high-order aspheric coefficients. The tables presented below for each embodiment are the corresponding schematic parameter, image plane curves and distortion curves, and the definitions of the tables are the same as Table 1 and Table 2 of the first embodiment. Therefore, an explanation in this regard will not be provided again. 
     Referring to  FIGS. 2A and 2B ,  FIG. 2A  shows a three-piece infrared single wavelength lens system in accordance with a second embodiment of the present invention, and  FIG. 2B  shows, in order from left to right, the image plane curve and the distortion curve of the second embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the second embodiment of the present invention comprises a stop  200  and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element  210 , a second lens element  220 , a third lens element  230 , an IR cut filter  270 , and an image plane  280 , wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop  200  is disposed between the first lens element  210  and the second lens element  220 . 
     The first lens element  210  with a negative refractive power has an object-side surface  211  being convex near an optical axis  290  and an image-side surface  212  being concave near the optical axis  290 , the object-side surface  211  and the image-side surface  212  are aspheric, and the first lens element  210  is made of plastic material. 
     The second lens element  220  with a positive refractive power has an object-side surface  221  being concave near the optical axis  290  and an image-side surface  222  being convex near the optical axis  290 , the object-side surface  221  and the image-side surface  222  are aspheric, and the second lens element  220  is made of plastic material. 
     The third lens element  230  with a positive refractive power has an object-side surface  231  being convex near the optical axis  290  and an image-side surface  232  being concave near the optical axis  290 , the object-side surface  231  and the image-side surface  232  are aspheric, the third lens element  230  is made of plastic material, and at least one of the object-side surface  231  and the image-side surface  232  is provided with at least one inflection point. 
     The IR cut filter  270  made of glass is located between the third lens element  230  and the image plane  280  and has no influence on the focal length of the three-piece infrared single wavelength lens system. 
     The detailed optical data of the second embodiment is shown in table 3, and the aspheric surface data is shown in table 4. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Embodiment 2 
               
               
                 f(focal length) = 1.49 mm, Fno = 2.0, FOV = 77.91 deg. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                 Focal 
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 0 
                 object 
                 infinity 
                 400 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 2 
                 Lens 1 
                 3.812 
                 (ASP) 
                 0.594 
                 plastic 
                 1.64 
                 22.46 
                 −2.79 
               
               
                 3 
                   
                 1.116 
                 (ASP) 
                 0.280 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 4 
                 stop 
                 infinity 
                 0.121 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 Lens 2 
                 −14.118 
                 (ASP) 
                 0.751 
                 plastic 
                 1.54 
                 56 
                 1.59 
               
               
                 6 
                   
                 −0.815 
                 (ASP) 
                 0.030 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 1.079 
                 (ASP) 
                 0.554 
                 plastic 
                 1.54 
                 56 
                 7.89 
               
               
                 8 
                   
                 1.191 
                 (ASP) 
                 0.571 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 9 
                 IR-filter 
                 infinity 
                 0.300 
                 glass 
                 1.517 
                 64.17 
                   
               
               
                 10 
                   
                 infinity 
                 0.554 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 — 
                   
                   
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Aspheric Coefficients 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 surface 
                 2 
                 3 
                 5 
                 6 
                 7 
                 8 
               
               
                   
               
               
                 K: 
                  6.1294E−01 
                  4.1054E+00 
                 −8.5037E+01 
                 −5.7819E+00 
                 −1.7078E+00 
                  3.0868E−01 
               
               
                 A: 
                  2.9587E−01 
                  9.8160E−01 
                  2.8199E−01 
                 −1.4358E+00 
                 −5.0194E−02 
                  3.3745E−01 
               
               
                 B: 
                 −8.5807E−02 
                  3.8457E−01 
                  1.1145E+00 
                  2.6237E+00 
                 −2.4864E−01 
                 −1.2885E+00 
               
               
                 C: 
                 −7.7507E−01 
                  1.0655E+01 
                 −1.4238E+01 
                 −5.4432E+00 
                  5.7364E−01 
                  1.4215E+00 
               
               
                 D: 
                  3.7345E+00 
                  6.2729E+00 
                  9.0630E+01 
                  7.7065E+00 
                 −7.9521E−01 
                 −1.1033E+00 
               
               
                 E: 
                 −7.1555E+00 
                  4.3767E+02 
                 −2.7077E+02 
                  3.2756E−01 
                 −1.8521E+00 
                 −3.2038E−02 
               
               
                 F 
                  6.5121E+00 
                 −4.6057E+03 
                  3.9975E+02 
                 −2.8291E+01 
                  4.9918E+00 
                  8.4759E−01 
               
               
                 G 
                 −2.3272E+00 
                  1.7582E+04 
                 −2.4111E+02 
                  4.3738E+01 
                 −3.1894E+00 
                 −5.1100E−01 
               
               
                   
               
            
           
         
       
     
     In the second embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the second embodiment, so an explanation in this regard will not be provided again. 
     Moreover, these parameters can be calculated from Table 3 and Table 4 as the following values and satisfy the following conditions: 
     
       
         
           
               
             
               
                   
               
               
                 Embodiment 2 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 f[mm] 
                 1.49 
                 f12/f3 
                 0.29 
               
               
                   
                 Fno 
                 2.0 
                 f/TL 
                 0.40 
               
               
                   
                 FOV[deg.] 
                 77.91 
                 R1/R2 
                 3.42 
               
               
                   
                 f/f12 
                 0.65 
                 R3/R4 
                 17.33 
               
               
                   
                 f/f23 
                 1.28 
                 R5/R6 
                 0.91 
               
               
                   
                 f1/f2 
                 −1.76 
                 CT1/CT2 
                 0.79 
               
               
                   
                 f2/f3 
                 0.20 
                 CT2/CT3 
                 1.36 
               
               
                   
                 f1/f3 
                 −0.35 
                 CT1/CT3 
                 1.07 
               
               
                   
                 f1/f23 
                 −2.40 
               
               
                   
                   
               
            
           
         
       
     
     Referring to  FIGS. 3A and 3B ,  FIG. 3A  shows a three-piece infrared single wavelength lens system in accordance with a third embodiment of the present invention, and  FIG. 3B  shows, in order from left to right, the image plane curve and the distortion curve of the third embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the third embodiment of the present invention comprises a stop  300  and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element  310 , a second lens element  320 , a third lens element  330 , an IR cut filter  370 , and an image plane  380 , wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop  300  is disposed between the first lens element  310  and the second lens element  320 . 
     The first lens element  310  with a negative refractive power has an object-side surface  311  being convex near an optical axis  390  and an image-side surface  312  being concave near the optical axis  390 , the object-side surface  311  and the image-side surface  312  are aspheric, and the first lens element  310  is made of plastic material. 
     The second lens element  320  with a positive refractive power has an object-side surface  321  being concave near the optical axis  390  and an image-side surface  322  being convex near the optical axis  390 , the object-side surface  321  and the image-side surface  322  are aspheric, and the second lens element  320  is made of plastic material. 
     The third lens element  330  with a positive refractive power has an object-side surface  331  being convex near the optical axis  390  and an image-side surface  332  being concave near the optical axis  390 , the object-side surface  331  and the image-side surface  332  are aspheric, the third lens element  330  is made of plastic material, and at least one of the object-side surface  331  and the image-side surface  332  is provided with at least one inflection point. 
     The IR cut filter  370  made of glass is located between the third lens element  330  and the image plane  380  and has no influence on the focal length of the three-piece infrared single wavelength lens system. 
     The detailed optical data of the third embodiment is shown in table 5, and the aspheric surface data is shown in table 6. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Embodiment 3 
               
               
                 f(focal length) = 1.49 mm, Fno = 2.0, FOV = 77.90 deg. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                 Focal 
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 0 
                 object 
                 infinity 
                 400 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 2 
                 Lens 1 
                 4.705 
                 (ASP) 
                 0.602 
                 plastic 
                 1.54 
                 56 
                 −2.98 
               
               
                 3 
                   
                 1.137 
                 (ASP) 
                 0.271 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 4 
                 stop 
                 infinity 
                 0.133 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 Lens 2 
                 −16.856 
                 (ASP) 
                 0.750 
                 plastic 
                 1.54 
                 56 
                 1.59 
               
               
                 6 
                   
                 −0.822 
                 (ASP) 
                 0.063 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 1.087 
                 (ASP) 
                 0.549 
                 plastic 
                 1.54 
                 56 
                 8.86 
               
               
                 8 
                   
                 1.162 
                 (ASP) 
                 0.570 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 9 
                 IR-filter 
                 infinity 
                 0.300 
                 glass 
                 1.517 
                 64.17 
                   
               
               
                 10 
                   
                 infinity 
                 0.525 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 — 
                   
                   
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Aspheric Coefficients 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 surface 
                 2 
                 3 
                 5 
                 6 
                 7 
                 8 
               
               
                   
               
               
                 K: 
                  3.8604E+00 
                  3.2101E+00 
                 −1.0001E+02 
                 −6.1038E+00 
                 −1.5996E+00 
                  2.6418E−01 
               
               
                 A: 
                  3.0709E−01 
                  1.0878E+00 
                  2.0179E−01 
                 −1.4445E+00 
                 −6.1041E−02 
                  2.9361E−01 
               
               
                 B: 
                 −1.1443E−01 
                  9.3265E−01 
                  1.2597E+00 
                  2.6941E+00 
                 −2.9449E−01 
                 −1.2264E+00 
               
               
                 C: 
                 −7.5850E−01 
                  1.5572E+01 
                 −1.3966E+01 
                 −5.5142E+00 
                  6.8511E−01 
                  1.3989E+00 
               
               
                 D: 
                  3.7253E+00 
                 −2.1114E+01 
                  9.0065E+01 
                  7.5212E+00 
                 −7.4286E−01 
                 −1.1461E+00 
               
               
                 E: 
                 −7.1213E+00 
                  3.5686E+02 
                 −2.7158E+02 
                  7.7397E−01 
                 −2.0586E+00 
                 −2.2590E−02 
               
               
                 F 
                  6.4293E+00 
                 −3.5542E+03 
                  3.9946E+02 
                 −2.7494E+01 
                  4.9270E+00 
                  9.4774E−01 
               
               
                 G 
                 −2.2747E+00 
                  1.6967E+04 
                 −2.3662E+02 
                  4.1759E+01 
                 −2.9126E+00 
                 −5.9429E−01 
               
               
                   
               
            
           
         
       
     
     In the third embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the third embodiment, so an explanation in this regard will not be provided again. 
     Moreover, these parameters can be calculated from Table 5 and Table 6 as the following values and satisfy the following conditions: 
     
       
         
           
               
             
               
                   
               
               
                 Embodiment 3 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 f[mm] 
                 1.49 
                 f12/f3 
                 0.25 
               
               
                   
                 Fno 
                 2.0 
                 f/TL 
                 0.40 
               
               
                   
                 FOV[deg.] 
                 77.90 
                 R1/R2 
                 4.14 
               
               
                   
                 f/f12 
                 0.68 
                 R3/R4 
                 20.50 
               
               
                   
                 f/f23 
                 1.25 
                 R5/R6 
                 0.94 
               
               
                   
                 f1/f2 
                 −1.87 
                 CT1/CT2 
                 0.80 
               
               
                   
                 f2/f3 
                 0.18 
                 CT2/CT3 
                 1.37 
               
               
                   
                 f1/f3 
                 −0.34 
                 CT1/CT3 
                 1.10 
               
               
                   
                 f1/f23 
                 −2.51 
               
               
                   
                   
               
            
           
         
       
     
     Referring to  FIGS. 4A and 4B ,  FIG. 4A  shows a three-piece infrared single wavelength lens system in accordance with a fourth embodiment of the present invention, and  FIG. 4B  shows, in order from left to right, the image plane curve and the distortion curve of the fourth embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the fourth embodiment of the present invention comprises a stop  400  and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element  410 , a second lens element  420 , a third lens element  430 , an IR cut filter  470 , and an image plane  480 , wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop  400  is disposed between the first lens element  410  and the second lens element  420 . 
     The first lens element  410  with a negative refractive power has an object-side surface  411  being convex near an optical axis  490  and an image-side surface  412  being concave near the optical axis  490 , the object-side surface  411  and the image-side surface  412  are aspheric, and the first lens element  410  is made of plastic material. 
     The second lens element  420  with a positive refractive power has an object-side surface  421  being concave near the optical axis  490  and an image-side surface  422  being convex near the optical axis  490 , the object-side surface  421  and the image-side surface  422  are aspheric, and the second lens element  420  is made of plastic material. 
     The third lens element  430  with a negative refractive power has an object-side surface  431  being convex near the optical axis  490  and an image-side surface  432  being concave near the optical axis  490 , the object-side surface  431  and the image-side surface  432  are aspheric, the third lens element  430  is made of plastic material, and at least one of the object-side surface  431  and the image-side surface  432  is provided with at least one inflection point. 
     The IR cut filter  470  made of glass is located between the third lens element  430  and the image plane  480  and has no influence on the focal length of the three-piece infrared single wavelength lens system. 
     The detailed optical data of the fourth embodiment is shown in table 7, and the aspheric surface data is shown in table 8. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Embodiment 4 
               
               
                 f(focal length) = 1.48 mm, Fno = 2.0, FOV = 77.92 deg. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                 Focal 
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 0 
                 object 
                 infinity 
                 400 
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0 
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 2 
                 Lens 1 
                 1.956 
                 (ASP) 
                 0.491 
                 plastic 
                 1.64 
                 22.46 
                 −3.90 
               
               
                 3 
                   
                 0.977 
                 (ASP) 
                 0.272 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 4 
                 stop 
                 infinity 
                 0.162 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 Lens 2 
                 −7.733 
                 (ASP) 
                 0.688 
                 plastic 
                 1.64 
                 22.46 
                 1.31 
               
               
                 6 
                   
                 −0.763 
                 (ASP) 
                 0.031 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 1.269 
                 (ASP) 
                 0.407 
                 plastic 
                 1.64 
                 22.46 
                 −78.93 
               
               
                 8 
                   
                 1.085 
                 (ASP) 
                 0.556 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 9 
                 IR-filter 
                 infinity 
                 0.300 
                 glass 
                 1.517 
                 64.17 
                   
               
               
                 10 
                   
                 infinity 
                 0.506 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 — 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Aspheric Coefficients 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 surface 
                 2 
                 3 
                 5 
                 6 
                 7 
                 8 
               
               
                   
               
               
                 K: 
                 −2.2390E+00 
                  4.1672E+00 
                  7.2309E+01 
                 −4.7502E+00 
                 −1.9112E+00 
                  1.4270E−01 
               
               
                 A: 
                  3.5786E−01 
                  7.9903E−01 
                  5.1762E−02 
                 −1.3765E+00 
                 −7.1093E−02 
                  8.8149E−02 
               
               
                 B: 
                  5.5728E−02 
                  1.2861E+00 
                  1.5493E+00 
                  2.7087E+00 
                 −3.5407E−01 
                 −1.1246E+00 
               
               
                 C: 
                 −5.7846E−01 
                  3.3499E+00 
                 −1.3171E+01 
                 −5.7142E+00 
                  6.9128E−01 
                  1.4349E+00 
               
               
                 D: 
                  3.6046E+00 
                  4.7493E+00 
                  8.8838E+01 
                  7.4603E+00 
                 −8.1157E−01 
                 −1.1405E+00 
               
               
                 E: 
                 −7.2812E+00 
                  3.9678E+02 
                 −2.7472E+02 
                  1.1838E+00 
                 −1.7842E+00 
                  1.6324E−02 
               
               
                 F 
                  6.6380E+00 
                 −4.4874E+03 
                  4.0815E+02 
                 −2.5526E+01 
                  5.4012E+00 
                  6.2446E−01 
               
               
                 G 
                 −1.3242E+00 
                  2.3249E+04 
                 −2.4394E+02 
                  4.2597E+01 
                 −3.9130E+00 
                 −3.9325E−01 
               
               
                   
               
            
           
         
       
     
     In the fourth embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the fourth embodiment, so an explanation in this regard will not be provided again. 
     Moreover, these parameters can be calculated from Table 7 and Table 8 as the following values and satisfy the following conditions: 
     
       
         
           
               
             
               
                   
               
               
                 Embodiment 4 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 f[mm] 
                 1.48 
                 f12/f3 
                 −0.02 
               
               
                   
                 Fno 
                 2.0 
                 f/TL 
                 0.43 
               
               
                   
                 FOV[deg.] 
                 77.92 
                 R1/R2 
                 2.00 
               
               
                   
                 f/f12 
                 0.89 
                 R3/R4 
                 10.14 
               
               
                   
                 f/f23 
                 1.27 
                 R5/R6 
                 1.17 
               
               
                   
                 f1/f2 
                 −2.97 
                 CT1/CT2 
                 0.71 
               
               
                   
                 f2/f3 
                 −0.02 
                 CT2/CT3 
                 1.69 
               
               
                   
                 f1/f3 
                 0.05 
                 CT1/CT3 
                 1.21 
               
               
                   
                 f1/f23 
                 −3.34 
               
               
                   
                   
               
            
           
         
       
     
     Referring to  FIGS. 5A and 5B ,  FIG. 5A  shows a three-piece infrared single wavelength lens system in accordance with a fifth embodiment of the present invention, and  FIG. 5B  shows, in order from left to right, the image plane curve and the distortion curve of the fifth embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the fifth embodiment of the present invention comprises a stop  500  and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element  510 , a second lens element  520 , a third lens element  530 , an IR cut filter  570 , and an image plane  580 , wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop  500  is disposed between the first lens element  510  and the second lens element  520 . 
     The first lens element  510  with a negative refractive power has an object-side surface  511  being convex near an optical axis  590  and an image-side surface  512  being concave near the optical axis  590 , the object-side surface  511  and the image-side surface  512  are aspheric, and the first lens element  510  is made of plastic material. 
     The second lens element  520  with a positive refractive power has an object-side surface  521  being concave near the optical axis  590  and an image-side surface  522  being convex near the optical axis  590 , the object-side surface  521  and the image-side surface  522  are aspheric, and the second lens element  520  is made of plastic material. 
     The third lens element  530  with a positive refractive power has an object-side surface  531  being convex near the optical axis  590  and an image-side surface  532  being concave near the optical axis  590 , the object-side surface  531  and the image-side surface  532  are aspheric, the third lens element  530  is made of plastic material, and at least one of the object-side surface  531  and the image-side surface  532  is provided with at least one inflection point. 
     The IR cut filter  570  made of glass is located between the third lens element  530  and the image plane  580  and has no influence on the focal length of the three-piece infrared single wavelength lens system. 
     The detailed optical data of the fifth embodiment is shown in table 9, and the aspheric surface data is shown in table 10. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Embodiment 5 
               
               
                 f(focal length) = 1.54 mm, Fno = 2.0, FOV = 74.94 deg. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                 Focal 
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 0 
                 object 
                 infinity 
                 400 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 2 
                 Lens 1 
                 2.202 
                 (ASP) 
                 0.590 
                 plastic 
                 1.64 
                 22.46 
                 −3.90 
               
               
                 3 
                   
                 1.035 
                 (ASP) 
                 0.313 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 4 
                 stop 
                 infinity 
                 0.160 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 Lens 2 
                 −10.566 
                 (ASP) 
                 0.701 
                 plastic 
                 1.64 
                 22.46 
                 1.49 
               
               
                 6 
                   
                 −0.869 
                 (ASP) 
                 0.068 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 1.322 
                 (ASP) 
                 0.501 
                 plastic 
                 1.64 
                 22.46 
                 17.49 
               
               
                 8 
                   
                 1.287 
                 (ASP) 
                 0.557 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 9 
                 IR-filter 
                 infinity 
                 0.300 
                 glass 
                 1.517 
                 64.17 
                   
               
               
                 10 
                   
                 infinity 
                 0.512 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 — 
                   
                   
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Aspheric Coefficients 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 surface 
                 2 
                 3 
                 5 
                 6 
                 7 
                 8 
               
               
                   
               
               
                 K: 
                 −7.8009E+00 
                  4.0019E+00 
                  8.2382E+01 
                 −6.3430E+00 
                 −2.5821E+00 
                  3.6935E−01 
               
               
                 A: 
                  3.2392E−01 
                  9.2476E−01 
                  4.3206E−02 
                 −1.3338E+00 
                 −5.4925E−02 
                  1.7484E−01 
               
               
                 B: 
                 −4.7520E−03 
                 −2.2725E+00 
                  1.5276E+00 
                  2.7900E+00 
                 −2.3750E−01 
                 −1.0033E+00 
               
               
                 C: 
                 −7.4350E−01 
                  1.6052E+01 
                 −1.3402E+01 
                 −5.6303E+00 
                  7.9650E−01 
                  1.4545E+00 
               
               
                 D: 
                  3.6126E+00 
                  2.0368E+01 
                  8.9465E+01 
                  7.5649E+00 
                 −7.8032E−01 
                 −1.2230E+00 
               
               
                 E: 
                 −7.0746E+00 
                  2.4563E+02 
                 −2.7315E+02 
                  1.5984E+00 
                 −2.0042E+00 
                  3.1563E−02 
               
               
                 F 
                  6.7177E+00 
                 −4.8788E+03 
                  4.0098E+02 
                 −2.5663E+01 
                  5.1399E+00 
                  8.3926E−01 
               
               
                 G 
                 −2.4136E+00 
                  1.9148E+04 
                 −2.3677E+02 
                  3.8274E+01 
                 −3.1164E+00 
                 −5.2049E−01 
               
               
                   
               
            
           
         
       
     
     In the fifth embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the fifth embodiment, so an explanation in this regard will not be provided again. 
     Moreover, these parameters can be calculated from Table 9 and Table 10 as the following values and satisfy the following conditions: 
     
       
         
           
               
             
               
                   
               
               
                 Embodiment 5 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 f[mm] 
                 1.54 
                 f12/f3 
                 0.11 
               
               
                   
                 Fno 
                 2.0 
                 f/TL 
                 0.42 
               
               
                   
                 FOV[deg.] 
                 74.94 
                 R1/R2 
                 2.13 
               
               
                   
                 f/f12 
                 0.78 
                 R3/R4 
                 12.15 
               
               
                   
                 f/f23 
                 1.28 
                 R5/R6 
                 1.03 
               
               
                   
                 f1/f2 
                 −2.63 
                 CT1/CT2 
                 0.84 
               
               
                   
                 f2/f3 
                 0.08 
                 CT2/CT3 
                 1.40 
               
               
                   
                 f1/f3 
                 −0.22 
                 CT1/CT3 
                 1.18 
               
               
                   
                 f1/f23 
                 −3.24 
               
               
                   
                   
               
            
           
         
       
     
     Referring to  FIGS. 6A and 6B ,  FIG. 6A  shows a three-piece infrared single wavelength lens system in accordance with a sixth embodiment of the present invention, and  FIG. 6B  shows, in order from left to right, the image plane curve and the distortion curve of the sixth embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the sixth embodiment of the present invention comprises a stop  600  and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element  610 , a second lens element  620 , a third lens element  630 , an IR cut filter  670 , and an image plane  680 , wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop  600  is disposed between the first lens element  610  and the second lens element  620 . 
     The first lens element  610  with a negative refractive power has an object-side surface  611  being convex near an optical axis  690  and an image-side surface  612  being concave near the optical axis  690 , the object-side surface  611  and the image-side surface  612  are aspheric, and the first lens element  610  is made of plastic material. 
     The second lens element  620  with a positive refractive power has an object-side surface  621  being concave near the optical axis  690  and an image-side surface  622  being convex near the optical axis  690 , the object-side surface  621  and the image-side surface  622  are aspheric, and the second lens element  620  is made of plastic material. 
     The third lens element  630  with a positive refractive power has an object-side surface  631  being convex near the optical axis  690  and an image-side surface  632  being concave near the optical axis  690 , the object-side surface  631  and the image-side surface  632  are aspheric, the third lens element  630  is made of plastic material, and at least one of the object-side surface  631  and the image-side surface  632  is provided with at least one inflection point. 
     The IR cut filter  670  made of glass is located between the third lens element  630  and the image plane  680  and has no influence on the focal length of the three-piece infrared single wavelength lens system. 
     The detailed optical data of the sixth embodiment is shown in table 11, and the aspheric surface data is shown in table 12. 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Embodiment 6 
               
               
                 f(focal length) = 1.57 mm, Fno = 2.1, FOV = 74.88 deg. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                 Focal 
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 0 
                 object 
                 infinity 
                 infinity 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 2 
                 Lens 1 
                 2.500 
                 (ASP) 
                 0.433 
                 plastic 
                 1.54 
                 56 
                 −26.05 
               
               
                 3 
                   
                 1.988 
                 (ASP) 
                 0.159 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 4 
                 stop 
                 infinity 
                 0.160 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 Lens 2 
                 −1.834 
                 (ASP) 
                 0.701 
                 plastic 
                 1.63 
                 23.9 
                 1.75 
               
               
                 6 
                   
                 −0.775 
                 (ASP) 
                 0.249 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 1.407 
                 (ASP) 
                 0.570 
                 plastic 
                 1.54 
                 56 
                 22.37 
               
               
                 8 
                   
                 1.375 
                 (ASP) 
                 0.503 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 9 
                 IR-filter 
                 infinity 
                 0.300 
                 glass 
                 1.517 
                 64.17 
                   
               
               
                 10 
                   
                 infinity 
                 0.326 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 — 
                   
                   
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Aspheric Coefficients 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 surface 
                 2 
                 3 
                 5 
                 6 
                 7 
                 8 
               
               
                   
               
               
                 K: 
                  5.2732E+00 
                  2.0909E+01 
                 −9.5305E−01 
                 −5.6895E+00 
                 −2.4514E+00 
                 −7.6091E−02 
               
               
                 A: 
                  3.3414E−01 
                  8.4239E−01 
                 −7.7180E−02 
                 −1.4036E+00 
                  2.0463E−03 
                  7.0750E−02 
               
               
                 B: 
                  2.7099E−01 
                 −7.1657E−01 
                  1.1784E+00 
                  2.7424E+00 
                 −9.5297E−02 
                 −2.4395E−01 
               
               
                 C: 
                 −2.4011E+00 
                  4.4395E+01 
                 −9.3653E+00 
                 −5.9797E+00 
                 −1.1786E−01 
                 −4.2916E−02 
               
               
                 D: 
                  1.0078E+01 
                 −2.3174E+02 
                  6.3816E+01 
                  5.0229E+00 
                 −8.2333E−03 
                  1.1159E−01 
               
               
                 E: 
                 −3.5750E+00 
                  1.3698E+02 
                 −2.8006E+02 
                  2.7918E−01 
                  7.3641E−02 
                  1.7417E−02 
               
               
                 F 
                 −3.8559E+01 
                  1.0939E+03 
                  8.6338E+02 
                 −2.1985E+00 
                  7.8696E−02 
                 −8.2864E−02 
               
               
                 G 
                  5.4058E+01 
                  9.4539E+03 
                 −1.2923E+03 
                 −2.9416E+00 
                 −2.0725E−01 
                  3.1924E−02 
               
               
                   
               
            
           
         
       
     
     In the sixth embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the sixth embodiment, so an explanation in this regard will not be provided again. 
     Moreover, these parameters can be calculated from Table 11 and Table 12 as the following values and satisfy the following conditions: 
     
       
         
           
               
             
               
                   
               
               
                 Embodiment 6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 f[mm] 
                 1.57 
                 f12/f3 
                 0.09 
               
               
                   
                 Fno 
                 2.1 
                 f/TL 
                 0.46 
               
               
                   
                 FOV[deg.] 
                 74.88 
                 R1/R2 
                 1.26 
               
               
                   
                 f/f12 
                 0.81 
                 R3/R4 
                 2.36 
               
               
                   
                 f/f23 
                 1.10 
                 R5/R6 
                 1.02 
               
               
                   
                 f1/f2 
                 −14.86 
                 CT1/CT2 
                 0.62 
               
               
                   
                 f2/f3 
                 0.08 
                 CT2/CT3 
                 1.23 
               
               
                   
                 f1/f3 
                 −1.16 
                 CT1/CT3 
                 0.76 
               
               
                   
                 f1/f23 
                 −18.15 
               
               
                   
                   
               
            
           
         
       
     
     Referring to  FIGS. 7A and 7B ,  FIG. 7A  shows a three-piece infrared single wavelength lens system in accordance with a seventh embodiment of the present invention, and  FIG. 7B  shows, in order from left to right, the image plane curve and the distortion curve of the seventh embodiment of the present invention. A three-piece infrared single wavelength lens system in accordance with the seventh embodiment of the present invention comprises a stop  700  and a lens group. The lens group comprises, in order from an object side to an image side: a first lens element  710 , a second lens element  720 , a third lens element  730 , an IR cut filter  770 , and an image plane  780 , wherein the three-piece infrared single wavelength lens system has a total of three lens elements with refractive power. The stop  700  is disposed between the first lens element  710  and the second lens element  720 . 
     The first lens element  710  with a negative refractive power has an object-side surface  711  being convex near an optical axis  790  and an image-side surface  712  being concave near the optical axis  790 , the object-side surface  711  and the image-side surface  712  are aspheric, and the first lens element  710  is made of plastic material. 
     The second lens element  720  with a positive refractive power has an object-side surface  721  being concave near the optical axis  790  and an image-side surface  722  being convex near the optical axis  790 , the object-side surface  721  and the image-side surface  722  are aspheric, and the second lens element  720  is made of plastic material. 
     The third lens element  730  with a positive refractive power has an object-side surface  731  being convex near the optical axis  790  and an image-side surface  732  being concave near the optical axis  790 , the object-side surface  731  and the image-side surface  732  are aspheric, the third lens element  730  is made of plastic material, and at least one of the object-side surface  731  and the image-side surface  732  is provided with at least one inflection point. 
     The IR cut filter  770  made of glass is located between the third lens element  730  and the image plane  780  and has no influence on the focal length of the three-piece infrared single wavelength lens system. 
     The detailed optical data of the seventh embodiment is shown in table 13, and the aspheric surface data is shown in table 14. 
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 Embodiment 7 
               
               
                 f(focal length) = 1.46 mm, Fno = 2.0, FOV = 84.9 deg. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                 Focal 
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 length 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 0 
                 object 
                 infinity 
                 infinity 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 2 
                 Lens 1 
                 2.268 
                 (ASP) 
                 0.604 
                 plastic 
                 1.54 
                 56 
                 −26.05 
               
               
                 3 
                   
                 0.942 
                 (ASP) 
                 0.270 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 4 
                 stop 
                 infinity 
                 0.138 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 Lens 2 
                 17.583 
                 (ASP) 
                 0.782 
                 plastic 
                 1.63 
                 23.9 
                 1.75 
               
               
                 6 
                   
                 −0.817 
                 (ASP) 
                 0.070 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 1.391 
                 (ASP) 
                 0.422 
                 plastic 
                 1.54 
                 56 
                 22.37 
               
               
                 8 
                   
                 1.235 
                 (ASP) 
                 0.546 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 9 
                 IR-filter 
                 infinity 
                 0.300 
                 glass 
                 1.517 
                 64.17 
                   
               
               
                 10 
                   
                 infinity 
                 0.501 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 — 
                   
                   
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 14 
               
             
            
               
                   
               
               
                 Aspheric Coefficients 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 surface 
                 2 
                 3 
                 5 
                 6 
                 7 
                 8 
               
               
                   
               
               
                 K: 
                 −9.7413E+00 
                  3.1682E+00 
                  1.0001E+02 
                 −5.3455E+00 
                 −3.2823E+00 
                  2.7202E−01 
               
               
                 A: 
                  3.1137E−01 
                  8.2309E−01 
                  3.7344E−03 
                 −1.3292E+00 
                 −6.1724E−02 
                  1.4826E−01 
               
               
                 B: 
                 −1.0515E−02 
                 −1.4297E+00 
                  1.1470E+00 
                  2.6637E+00 
                 −3.0264E−01 
                 −1.0266E+00 
               
               
                 C: 
                 −7.6675E−01 
                  1.6638E+01 
                 −1.3918E+01 
                 −5.7517E+00 
                  7.3444E−01 
                  1.4292E+00 
               
               
                 D: 
                  3.6057E+00 
                  2.6176E+00 
                  9.0309E+01 
                  7.6743E+00 
                 −8.3905E−01 
                 −1.2264E+00 
               
               
                 E: 
                 −7.0811E+00 
                  2.3399E+02 
                 −2.7074E+02 
                  1.6806E+00 
                 −2.0145E+00 
                  2.5782E−02 
               
               
                 F 
                  6.7095E+00 
                 −4.7000E+03 
                  4.0328E+02 
                 −2.6807E+01 
                  5.1297E+00 
                  8.7831E−01 
               
               
                 G 
                 −2.4452E+00 
                  1.9814E+04 
                 −2.4640E+02 
                  3.4028E+01 
                 −2.8834E+00 
                 −4.9463E−01 
               
               
                   
               
            
           
         
       
     
     In the seventh embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the first embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the first embodiment with corresponding values for the seventh embodiment, so an explanation in this regard will not be provided again. 
     Moreover, these parameters can be calculated from Table 13 and Table 14 as the following values and satisfy the following conditions: 
     
       
         
           
               
             
               
                   
               
               
                 Embodiment 7 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 f[mm] 
                 1.46 
                 f12/f3 
                 0.003 
               
               
                   
                 Fno 
                 2.0 
                 f/TL 
                 0.40 
               
               
                   
                 FOV[deg.] 
                 84.90 
                 R1/R2 
                 2.41 
               
               
                   
                 f/f12 
                 0.88 
                 R3/R4 
                 −21.53 
               
               
                   
                 f/f23 
                 1.30 
                 R5/R6 
                 1.13 
               
               
                   
                 f1/f2 
                 −2.46 
                 CT1/CT2 
                 0.77 
               
               
                   
                 f2/f3 
                 0.002 
                 CT2/CT3 
                 1.85 
               
               
                   
                 f1/f3 
                 −0.01 
                 CT1/CT3 
                 1.43 
               
               
                   
                 f1/f23 
                 −2.79 
               
               
                   
                   
               
            
           
         
       
     
     In the present three-piece infrared single wavelength lens system, the lens elements can be made of plastic or glass. If the lens elements are made of plastic, the cost will be effectively reduced. If the lens elements are made of glass, there is more freedom in distributing the refractive power of the three-piece infrared single wavelength lens system. Plastic lens elements can have aspheric surfaces, which allow more design parameter freedom (than spherical surfaces), so as to reduce the aberration and the number of the lens elements, as well as the total track length of the three-piece infrared single wavelength lens system. 
     In the present three-piece infrared single wavelength lens system, if the object-side or the image-side surface of the lens elements with refractive power is convex and the location of the convex surface is not defined, the object-side or the image-side surface of the lens elements near the optical axis is convex. If the object-side or the image-side surface of the lens elements is concave and the location of the concave surface is not defined, the object-side or the image-side surface of the lens elements near the optical axis is concave. 
     The three-piece infrared single wavelength lens system of the present invention can be used in focusing optical systems and can obtain better image quality. The three-piece infrared single wavelength lens system of the present invention can also be used in electronic imaging systems, such as, 3D image capturing, digital camera, mobile device, digital flat panel or vehicle camera. 
     While we have shown and described various embodiments in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.