Abstract:
A three-piece infrared single wavelength lens system includes, in order from the object side to the image side: a stop, a first lens element with a positive refractive power, a second lens element with a positive refractive power, and a third lens element with a positive refractive power. 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: 0.5&lt;f1/f23&lt;1.0. When the above relation is satisfied, a wide field of view can be obtained and the resolution can be improved evidently.

Description:
[0001]    BACKGROUND 
         [0002]    Field of the Invention 
         [0003]    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. 
         [0004]    Description of the Prior Art 
         [0005]    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 
         [0006]    (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. 
         [0007]    The applicant has also put forward a number of lens groups related to infrared wavelength reception, such as the single focus wide-angle lens modules disclosed in TW Appl. Nos. 098100552, 098125378 and U.S. Pat. Nos. 8,031,413, 8,369,031, 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. 
         [0008]    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. 
         [0009]    The present invention mitigates and/or obviates the aforementioned disadvantages. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is aimed at providing a three-piece infrared single wavelength lens system with better image sensing function. 
         [0011]    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 stop; a first lens element with a positive refractive power, having an object-side surface being convex near an optical axis and an image-side surface being convex 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 second lens element with a positive refractive power, having an object-side surface being concave near the optical axis and an image-side surface being convex near the optical axis, at least one of the object-side surface and the image-side surface of the second lens element being aspheric; and a third lens element with a positive 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. 
         [0012]    A focal length of the first lens element is f1, a focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.5&lt;f1/f23&lt;1.0, so that a wide field of view can be obtained and the resolution can be improved evidently. 
         [0013]    Preferably, the focal length of the first lens element is f1, a focal length of the second lens element is f2, and they satisfy the relation: 0.05&lt;f1/f2&lt;0.45, so that the refractive power of the first lens element and the second lens element are more suitable, it will be favorable to obtain a wide field of view and avoid the excessive increase of aberration of the system. 
         [0014]    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: 0.5&lt;f2/f3&lt;2.6, so that the refractive power of the second lens element and the third lens element are more balanced, it will be favorable to correct the aberration of the system and reduce the sensitivity of the system. 
         [0015]    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: 0.05&lt;f1/f3&lt;0.7, so that the positive refractive power of the first lens element can be distributed effectively, so as to reduce the sensitivity of the three-piece infrared single wavelength lens system. 
         [0016]    Preferably, a 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: 0.1&lt;f12/f3&lt;0.65, so that a wide field of view can be obtained and the resolution can be improved evidently. 
         [0017]    Preferably, a radius of curvature of the image-side surface of the first lens element is R2, a radius of curvature of the object-side surface of the second lens element is R3, and they satisfy the relation: 25&lt;R2/R3&lt;270, which can reduce the spherical aberration and astigmatism of the three-piece infrared single wavelength lens system. 
         [0018]    Preferably, the three-piece infrared single wavelength lens system has a maximum view angle FOV, and it satisfies the relation: 45&lt;FOV&lt;75, so that the three-piece infrared single wavelength lens system will have an appropriately large field of view. 
         [0019]    Preferably, a central thickness of the first lens element along the optical axis is CT1, a distance along the optical axis between the first lens element and the second lens element is T12, and they satisfy the relation: 1.4&lt;CT1/T12&lt;2.4, which is favorable to the assembly of the lens group, improving the yield of production. 
         [0020]    Preferably, the distance along the optical axis between the first lens element and the second lens element is T12, a central thickness of the second lens element along the optical axis is CT2, and they satisfy the relation: 0.5&lt;T12/CT2&lt;1.4, which is favorable to the formation and homogeneity of lenses and can increase the yield of assembly. 
         [0021]    Preferably, the distance along the optical axis between the first lens element and the second lens element is T12, a distance along the optical axis between the second lens element and the third lens element is T23, and they satisfy the relation: 5.4&lt;T12/T23&lt;9.0, so that the distance between the lens elements is more suitable, it will be favorable to the assembly of the lenses, increasing the yield of finished products. 
         [0022]    Preferably, an Abbe number of the first lens element is V1, an Abbe number of the second lens element is V2, and they satisfy the relation: 30&lt;V1-V2&lt;42, which can reduce the spherical aberration and astigmatism of the three-piece infrared single wavelength lens system effectively. 
         [0023]    Preferably, the Abbe number of the first lens element is V1, an Abbe number of the third lens element is V3, and they satisfy the relation: 30&lt;V1-V3&lt;42, so that the chromatic aberration of the three-piece infrared single wavelength lens system can be modified effectively, improving the image quality. 
         [0024]    Preferably, a f-number of the three-piece infrared single wavelength lens system is Fno, and it satisfies the relation: 1.2&lt;Fno&lt;1.8, so that the size of the stop of the three-piece infrared single wavelength lens system can be adjusted properly, making the three-piece infrared single wavelength lens system has a big stop. 
         [0025]    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 
         [0026]      FIG. 1A  shows a three-piece infrared single wavelength lens system in accordance with a first embodiment of the present invention; 
           [0027]      FIG. 1B  shows the longitudinal spherical aberration curve, the astigmatic field curve and the distortion curve of the first embodiment of the present invention; 
           [0028]      FIG. 2A  shows a three-piece infrared single wavelength lens system in accordance with a second embodiment of the present invention; 
           [0029]      FIG. 2B  shows the longitudinal spherical aberration curve, the astigmatic field curve and the distortion curve of the second embodiment of the present invention; 
           [0030]      FIG. 3A  shows a three-piece infrared single wavelength lens system in accordance with a third embodiment of the present invention; 
           [0031]      FIG. 3B  shows the longitudinal spherical aberration curve, the astigmatic field curve and the distortion curve of the third embodiment of the present invention; 
           [0032]      FIG. 4A  shows a three-piece infrared single wavelength lens system in accordance with a fourth embodiment of the present invention; and 
           [0033]      FIG. 4B  shows the longitudinal spherical aberration curve, the astigmatic field curve and the distortion curve of the fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    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 longitudinal spherical aberration curves, the astigmatic field curves, 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 an image-side surface  112  of the first lens element  110  and an object to be imaged. 
         [0035]    The first lens element  110  with a positive refractive power has an object-side surface  111  being convex near an optical axis  190  and the image-side surface  112  being convex 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. 
         [0036]    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. 
         [0037]    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, and the third lens element  130  is made of plastic material. 
         [0038]    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. 
         [0039]    The equation for the aspheric surface profiles of the respective lens elements of the first embodiment is expressed as follows: 
         [0040]    wherein: 
         [0000]    
       
         
           
             z 
             = 
             
               
                 
                   ch 
                   2 
                 
                 
                   1 
                   + 
                   
                     
                       [ 
                       
                         1 
                         - 
                         
                           
                             ( 
                             
                               k 
                               + 
                               1 
                             
                             ) 
                           
                            
                           
                             c 
                             2 
                           
                            
                           
                             h 
                             2 
                           
                         
                       
                       ] 
                     
                     0.5 
                   
                 
               
               + 
               
                 Ah 
                 4 
               
               + 
               
                 Bh 
                 6 
               
               + 
               
                 Ch 
                 8 
               
               + 
               
                 Dh 
                 10 
               
               + 
               
                 Eh 
                 12 
               
               + 
               
                 Gh 
                 14 
               
               + 
               … 
             
           
         
       
     
         [0041]    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 ; 
         [0042]    c represents a paraxial curvature equal to 1/R (R: a paraxial radius of curvature); 
         [0043]    h represents a vertical distance from the point on the curve of the aspheric surface to the optical axis  190 ; 
         [0044]    k represents the conic constant; 
         [0045]    A, B, C, D, E, G, . . . : represent the high-order aspheric coefficients. 
         [0046]    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=1.192 mm; Fno=1.4; and FOV=60 degrees. 
         [0047]    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  and the third lens element  130  combined is f23, and they satisfy the relation: f1/f23=0.64636. 
         [0048]    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, a focal length of the second lens element  120  is f2, and they satisfy the relation: f1/f2=0.22985. 
         [0049]    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=1.39174. 
         [0050]    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=0.31990. 
         [0051]    In the first embodiment of the present three-piece infrared single wavelength lens system, a 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=0.32798. 
         [0052]    In the first embodiment of the present three-piece infrared single wavelength lens system, a radius of curvature of the image-side surface  112  of the first lens element  110  is R2, a radius of curvature of the object-side surface  121  of the second lens element  120  is R3, and they satisfy the relation: R2/R3=261.90368. 
         [0053]    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 distance along the optical axis  190  between the first lens element  110  and the second lens element  120  is T12, and they satisfy the relation: CT1/T12=1.85473. 
         [0054]    In the first embodiment of the present three-piece infrared single wavelength lens system, the distance along the optical axis  190  between the first lens element  110  and the second lens element  120  is T12, a central thickness of the second lens element  120  along the optical axis  190  is CT2, and they satisfy the relation: T12/CT2=0.97384. 
         [0055]    In the first embodiment of the present three-piece infrared single wavelength lens system, the distance along the optical axis  190  between the first lens element  110  and the second lens element  120  is T12, a distance along the optical axis  190  between the second lens element  120  and the third lens element  130  is T23, and they satisfy the relation: T12/T23=7.159. 
         [0056]    In the first embodiment of the present three-piece infrared single wavelength lens system, an Abbe number of the first lens element  110  is V1, an Abbe number of the second lens element  120  is V2, and they satisfy the relation: V1-V2=34.5. 
         [0057]    In the first embodiment of the present three-piece infrared single wavelength lens system, the Abbe number of the first lens element  110  is V1, an Abbe number of the third lens element  130  is V3, and they satisfy the relation: V1-V3=34.5. 
         [0058]    The detailed optical data of the first embodiment is shown in table 1, and the aspheric surface data is shown in table 2. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Embodiment 1 
               
               
                 f(focal length) = 1.192 mm, Fno = 1.4, FOV = 60 deg. 
               
             
          
           
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                   
               
               
                 surface 
                   
                 Radius 
                 Thickness  
                 Material 
                 Index 
                 Abbe # 
                 Focal length 
               
               
                   
               
             
          
           
               
                 0 
                 object 
                 infinity 
                 500.000 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0.002 
                   
                   
                   
                   
               
               
                 2 
                 stop 
                 infinity 
                 −0.002 
                   
                   
                   
                   
               
             
          
           
               
                 3 
                 Lens 1 
                 0.866 
                 (ASP) 
                 0.398 
                 plastic 
                 1.544 
                 56.000 
                 1.610 
               
               
                 4 
                   
                 −107.896 
                 (ASP) 
                 0.215 
                   
                   
                   
                   
               
               
                 5 
                 Lens 2 
                 −0.412 
                 (ASP) 
                 0.221 
                 plastic 
                 1.651 
                 21.500 
                 7.005 
               
               
                 6 
                   
                 −0.454 
                 (ASP) 
                 0.030 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 0.658 
                 (ASP) 
                 0.256 
                 plastic 
                 1.651 
                 21.500 
                 5.034 
               
               
                 8 
                   
                 0.707 
                 (ASP) 
                 0.379 
                   
                   
                   
                   
               
             
          
           
               
                 9 
                 IR-filter 
                 infinity 
                 0.210 
                 glass 
                 1.517 
                 64.167 
                 — 
               
               
                 10 
                   
                 infinity 
                 0.131 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 0.000 
                   
                   
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Aspheric Coefficients 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 surface 
               
             
          
           
               
                   
                   
                 3 
                 4 
                 5 
               
               
                   
                   
               
               
                   
                 K: 
                 1.6561E−01 
                 9.0001E+01 
                 −5.0677E−01 
               
               
                   
                 A: 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                 B: 
                 −1.7783E−01 
                 −3.8297E−01 
                 2.8597E+00 
               
               
                   
                 C: 
                 2.2848E+00 
                 7.7170E+00 
                 −5.9554E+00 
               
               
                   
                 D: 
                 −5.8170E+01 
                 −1.3481E+02 
                 −6.6323E+01 
               
               
                   
                 E: 
                 5.3783E+02 
                 1.0727E+03 
                 1.1671E+03 
               
               
                   
                 F: 
                 −2.3081E+03 
                 −3.8622E+03 
                 −4.7624E+03 
               
               
                   
                 G 
                 3.4798E+03 
                 4.9505E+03 
                 6.3678E+03 
               
               
                   
                 H 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                   
               
             
          
           
               
                   
                 surface 
               
             
          
           
               
                   
                   
                 6 
                 7 
                 8 
               
               
                   
                   
               
               
                   
                 K: 
                 −1.5487E+00 
                 −1.1929E+01 
                 −6.9879E+00 
               
               
                   
                 A: 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                 B: 
                 −4.3135E−01 
                 2.0091E+00 
                 −5.2294E−01 
               
               
                   
                 C: 
                 5.6008E+00 
                 −2.1131E+01 
                 1.5078E+00 
               
               
                   
                 D: 
                 −5.8963E+01 
                 1.1419E+02 
                 −1.1792E+01 
               
               
                   
                 E: 
                 3.4446E+02 
                 −3.9602E+02 
                 3.2929E+01 
               
               
                   
                 F: 
                 −7.4388E+02 
                 7.4075E+02 
                 −5.7999E+01 
               
               
                   
                 G 
                 5.0956E+02 
                 −6.2921E+02 
                 4.4847E+01 
               
               
                   
                 H 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                   
               
             
          
         
       
     
         [0059]    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, H . . . : represent the high-order aspheric coefficients. The tables presented below for each embodiment are the corresponding schematic parameter and aberration 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. 
         [0060]    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 longitudinal spherical aberration curves, the astigmatic field curves, 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 an image-side surface  212  of the first lens element  210  and an object to be imaged. 
         [0061]    The first lens element  210  with a positive refractive power has an object-side surface  211  being convex near an optical axis  290  and the image-side surface  212  being convex 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. 
         [0062]    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. 
         [0063]    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, and the third lens element  230  is made of plastic material. 
         [0064]    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. 
         [0065]    The detailed optical data of the second embodiment is shown in table 3, and the aspheric surface data is shown in table 4. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Embodiment 2 
               
               
                 f(focal length) = 1.264 mm, Fno = 1.4, FOV = 55 deg. 
               
             
          
           
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                   
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 Focal length 
               
               
                   
               
             
          
           
               
                 0 
                 object 
                 infinity 
                 500.000 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0.003 
                   
                   
                   
                   
               
               
                 2 
                 stop 
                 infinity 
                 −0.003 
                   
                   
                   
                   
               
             
          
           
               
                 3 
                 Lens 1 
                 0.956 
                 (ASP) 
                 0.479 
                 plastic 
                 1.544 
                 56.000 
                 1.760 
               
               
                 4 
                   
                 −56.134 
                 (ASP) 
                 0.258 
                   
                   
                   
                   
               
               
                 5 
                 Lens 2 
                 −0.453 
                 (ASP) 
                 0.221 
                 plastic 
                 1.651 
                 21.500 
                 9.111 
               
               
                 6 
                   
                 −0.499 
                 (ASP) 
                 0.030 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 0.669 
                 (ASP) 
                 0.274 
                 plastic 
                 1.651 
                 21.500 
                 4.227 
               
               
                 8 
                   
                 0.752 
                 (ASP) 
                 0.367 
                   
                   
                   
                   
               
             
          
           
               
                 9 
                 IR-filter 
                 infinity 
                 0.210 
                 glass 
                 1.517 
                 64.167 
                 — 
               
               
                 10 
                   
                 infinity 
                 0.144 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 0.000 
                   
                   
                   
                   
               
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Aspheric Coefficients 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 surface 
               
             
          
           
               
                   
                   
                 3 
                 4 
                 5 
               
               
                   
                   
               
               
                   
                 K: 
                 1.4591E−01 
                 8.6453E+03 
                 −5.0418E−01 
               
               
                   
                 A: 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                 B: 
                 −1.4983E−01 
                 −2.5141E−01 
                 2.1650E+00 
               
               
                   
                 C: 
                 1.4038E+00 
                 4.8007E+00 
                 −3.7831E+00 
               
               
                   
                 D: 
                 −2.9628E+01 
                 −6.9229E+01 
                 −3.4353E+01 
               
               
                   
                 E: 
                 2.2943E+02 
                 4.5491E+02 
                 4.9418E+02 
               
               
                   
                 F: 
                 −8.0646E+02 
                 −1.3541E+03 
                 −1.6700E+03 
               
               
                   
                 G 
                 1.0122E+03 
                 1.4330E+03 
                 1.8433E+03 
               
               
                   
                 H 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                   
               
             
          
           
               
                   
                 surface 
               
             
          
           
               
                   
                   
                 6 
                 7 
                 8 
               
               
                   
                   
               
               
                   
                 K: 
                 −1.4998E+00 
                 −1.0282E+01 
                 −5.4983E+00 
               
               
                   
                 A: 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                 B: 
                 −3.2878E−01 
                 1.8526E+00 
                 −8.3680E−02 
               
               
                   
                 C: 
                 3.5347E+00 
                 −1.3143E+01 
                 1.1134E+00 
               
               
                   
                 D: 
                 −3.0133E+01 
                 5.8273E+01 
                 −6.4602E+00 
               
               
                   
                 E: 
                 1.4609E+02 
                 −1.6768E+02 
                 1.3145E+01 
               
               
                   
                 F: 
                 −2.6120E+02 
                 2.6112E+02 
                 −2.0481E+01 
               
               
                   
                 G 
                 1.4485E+02 
                 −1.7938E+02 
                 1.5542E+01 
               
               
                   
                 H 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                   
               
             
          
         
       
     
         [0066]    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. 
         [0067]    Moreover, these parameters can be calculated from Table 3 and Table 4 as the following values and satisfy the following conditions: 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Embodiment 2 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 f 
                 1.264 
                 f12/f3 
                 0.43356 
               
               
                   
                 Fno 
                 1.4 
                 R2/R3 
                 123.96486 
               
               
                   
                 FOV 
                 55 
                 CT1/T12 
                 1.85478 
               
               
                   
                 f1/f2 
                 0.19314 
                 T12/CT2 
                 1.16877 
               
               
                   
                 f2/f3 
                 2.15539 
                 T12/T23 
                 8.60333 
               
               
                   
                 f1/f3 
                 0.41629 
                 V1 − V2 
                 34.5 
               
               
                   
                 f1/f23 
                 0.71360 
                 V1 − V3 
                 34.5 
               
               
                   
                   
               
             
          
         
       
     
         [0068]    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 longitudinal spherical aberration curves, the astigmatic field curves, 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 an image-side surface  312  of the first lens element  310  and an object to be imaged. 
         [0069]    The first lens element  310  with a positive refractive power has an object-side surface  311  being convex near an optical axis  390  and the image-side surface  312  being convex 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. 
         [0070]    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. 
         [0071]    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, and the third lens element  330  is made of plastic material. 
         [0072]    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. 
         [0073]    The detailed optical data of the third embodiment is shown in table 5, and the aspheric surface data is shown in table 6. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Embodiment 3 
               
               
                 f(focal length) = 1.076 mm, Fno = 1.6, FOV = 65 deg. 
               
             
          
           
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                   
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 Focal length 
               
               
                   
               
             
          
           
               
                 0 
                 object 
                 infinity 
                 500.000 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 −0.054 
                   
                   
                   
                   
               
               
                 2 
                 stop 
                 infinity 
                 0.054 
                   
                   
                   
                   
               
             
          
           
               
                 3 
                 Lens 1 
                 0.876 
                 (ASP) 
                 0.358 
                 plastic 
                 1.544 
                 56.000 
                 1.602 
               
               
                 4 
                   
                 −37.188 
                 (ASP) 
                 0.211 
                   
                   
                   
                   
               
               
                 5 
                 Lens 2 
                 −0.412 
                 (ASP) 
                 0.213 
                 plastic 
                 1.651 
                 21.500 
                 7.268 
               
               
                 6 
                   
                 −0.453 
                 (ASP) 
                 0.030 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 0.626 
                 (ASP) 
                 0.254 
                 plastic 
                 1.651 
                 21.500 
                 3.216 
               
               
                 8 
                   
                 0.764 
                 (ASP) 
                 0.333 
                   
                   
                   
                   
               
             
          
           
               
                 9 
                 IR-filter 
                 infinity 
                 0.210 
                 glass 
                 1.517 
                 64.167 
                 — 
               
               
                 10 
                   
                 infinity 
                 0.131 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 0.000 
                   
                   
                   
                   
               
             
          
           
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                 Aspheric Coefficients 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 surface 
               
             
          
           
               
                   
                   
                 3 
                 4 
                 5 
               
               
                   
                   
               
               
                   
                 K: 
                 1.1143E−01 
                 4.5584E+03 
                 −5.0524E−01 
               
               
                   
                 A: 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                 B: 
                 −2.6472E−01 
                 −4.3381E−01 
                 3.0370E+00 
               
               
                   
                 C: 
                 2.4231E+00 
                 1.0284E+01 
                 −1.0318E+01 
               
               
                   
                 D: 
                 −3.2150E+01 
                 −1.4021E+02 
                 −1.4086E+01 
               
               
                   
                 E: 
                 1.7801E+02 
                 9.7852E+02 
                 8.8790E+02 
               
               
                   
                 F: 
                 −6.4089E+02 
                 −3.3473E+03 
                 −4.0655E+03 
               
               
                   
                 G 
                 8.4568E+02 
                 4.1659E+03 
                 5.7099E+03 
               
               
                   
                 H 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                   
               
             
          
           
               
                   
                 surface 
               
             
          
           
               
                   
                   
                 6 
                 7 
                 8 
               
               
                   
                   
               
               
                   
                 K: 
                 −1.4714E+00 
                 −1.2397E+01 
                 −6.4401E+00 
               
               
                   
                 A: 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                 B: 
                 −4.9828E−01 
                 2.6913E+00 
                 −4.5859E−01 
               
               
                   
                 C: 
                 6.5987E+00 
                 −2.3621E+01 
                 5.1313E+00 
               
               
                   
                 D: 
                 −7.6651E+01 
                 1.2891E+02 
                 −3.6777E+01 
               
               
                   
                 E: 
                 4.6447E+02 
                 −4.6825E+02 
                 1.1797E+02 
               
               
                   
                 F: 
                 −1.0766E+03 
                 9.5965E+02 
                 −1.9549E+02 
               
               
                   
                 G 
                 8.5055E+02 
                 −8.6698E+02 
                 1.2566E+02 
               
               
                   
                 H 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                   
               
             
          
         
       
     
         [0074]    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. 
         [0075]    Moreover, these parameters can be calculated from Table 5 and Table 6 as the following values and satisfy the following conditions: 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Embodiment 3 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 f 
                 1.076 
                 f12/f3 
                 0.50896 
               
               
                   
                 Fno 
                 1.6 
                 R2/R3 
                 90.34390 
               
               
                   
                 FOV 
                 65 
                 CT1/T12 
                 1.69914 
               
               
                   
                 f1/f2 
                 0.22035 
                 T12/CT2 
                 0.98882 
               
               
                   
                 f2/f3 
                 2.26020 
                 T12/T23 
                 7.01767 
               
               
                   
                 f1/f3 
                 0.49804 
                 V1 − V2 
                 34.5 
               
               
                   
                 f1/f23 
                 0.84401 
                 V1 − V3 
                 34.5 
               
               
                   
                   
               
             
          
         
       
     
         [0076]    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 longitudinal spherical aberration curves, the astigmatic field curves, 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 an image-side surface  412  of the first lens element  410  and an object to be imaged. 
         [0077]    The first lens element  410  with a positive refractive power has an object-side surface  411  being convex near an optical axis  490  and the image-side surface  412  being convex 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. 
         [0078]    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. 
         [0079]    The third lens element  430  with a positive 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, and the third lens element  430  is made of plastic material. 
         [0080]    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. 
         [0081]    The detailed optical data of the fourth embodiment is shown in table 7, and the aspheric surface data is shown in table 8. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Embodiment 4 
               
               
                 f(focal length) = 1.11 mm, Fno = 1.4, FOV = 64 deg. 
               
             
          
           
               
                   
                   
                 Curvature 
                   
                   
                   
                   
                   
               
               
                 surface 
                   
                 Radius 
                 Thickness 
                 Material 
                 Index 
                 Abbe # 
                 Focal length 
               
               
                   
               
             
          
           
               
                 0 
                 object 
                 infinity 
                 500.000 
                   
                   
                   
                   
               
               
                 1 
                   
                 infinity 
                 0.000 
                   
                   
                   
                   
               
               
                 2 
                 stop 
                 infinity 
                 0.000 
                   
                   
                   
                   
               
             
          
           
               
                 3 
                 Lens 1 
                 0.848 
                 (ASP) 
                 0.364 
                 plastic 
                 1.544 
                 56.000 
                 1.508 
               
               
                 4 
                   
                 −13.555 
                 (ASP) 
                 0.173 
                   
                   
                   
                   
               
               
                 5 
                 Lens 2 
                 −0.416 
                 (ASP) 
                 0.234 
                 plastic 
                 1.635 
                 23.900 
                 5.081 
               
               
                 6 
                   
                 −0.445 
                 (ASP) 
                 0.030 
                   
                   
                   
                   
               
               
                 7 
                 Lens 3 
                 0.612 
                 (ASP) 
                 0.236 
                 plastic 
                 1.635 
                 23.900 
                 6.070 
               
               
                 8 
                   
                 0.625 
                 (ASP) 
                 0.358 
                   
                   
                   
                   
               
             
          
           
               
                 9 
                 IR-filter 
                 infinity 
                 0.210 
                 glass 
                 1.517 
                 64.167 
                 — 
               
               
                 10 
                   
                 infinity 
                 0.131 
                   
                   
                   
                   
               
               
                 11 
                 Image 
                 infinity 
                 0.000 
                   
                   
                   
                   
               
             
          
           
               
                   
                 plane 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 8 
               
               
                   
               
               
                 Aspheric coefficients 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 surface 
               
             
          
           
               
                   
                   
                 3 
                 4 
                 5 
               
               
                   
                   
               
               
                   
                 K: 
                 −6.8165E−02 
                 −6.6204E+01 
                 −5.5086E−01 
               
               
                   
                 A: 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                 B: 
                 −9.2855E−02 
                 −3.9781E−01 
                 2.8075E+00 
               
               
                   
                 C: 
                 −1.7300E+00 
                 −9.5082E−01 
                 −1.4380E+01 
               
               
                   
                 D: 
                 −1.1434E+01 
                 7.3878E+00 
                 1.3482E+02 
               
               
                   
                 E: 
                 3.1050E+02 
                 2.2340E+00 
                 −3.5346E+02 
               
               
                   
                 F: 
                 −2.3349E+03 
                 −1.6160E+02 
                 3.2516E+02 
               
               
                   
                 G 
                 5.0324E+03 
                 3.4273E+02 
                 −1.3212E+01 
               
               
                   
                 H 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                   
               
             
          
           
               
                   
                 surface 
               
             
          
           
               
                   
                   
                 6 
                 7 
                 8 
               
               
                   
                   
               
               
                   
                 K: 
                 −1.6842E+00 
                 −1.0036E+01 
                 −6.3872E+00 
               
               
                   
                 A: 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                 B: 
                 −4.2370E−01 
                 2.1256E+00 
                 −2.1000E−01 
               
               
                   
                 C: 
                 2.6819E+00 
                 −2.0101E+01 
                 5.4441E−01 
               
               
                   
                 D: 
                 8.1475E+00 
                 1.1789E+02 
                 −5.4072E+00 
               
               
                   
                 E: 
                 −8.0008E+01 
                 −4.9289E+02 
                 −5.1579E+00 
               
               
                   
                 F: 
                 4.9479E+02 
                 1.1501E+03 
                 3.0434E+01 
               
               
                   
                 G 
                 −8.8479E+02 
                 −1.2123E+03 
                 −2.9698E+01 
               
               
                   
                 H 
                 0.0000E+00 
                 0.0000E+00 
                 0.0000E+00 
               
               
                   
                   
               
             
          
         
       
     
         [0082]    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. 
         [0083]    Moreover, these parameters can be calculated from Table 7 and Table 8 as the following values and satisfy the following conditions: 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Embodiment 4 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 f 
                 1.11 
                 f12/f3 
                 0.24379 
               
               
                   
                 Fno 
                 1.4 
                 R2/R3 
                 32.60571 
               
               
                   
                 FOV 
                 64 
                 CT1/T12 
                 2.10076 
               
               
                   
                 f1/f2 
                 0.29673 
                 T12/CT2 
                 0.74124 
               
               
                   
                 f2/f3 
                 0.83702 
                 T12/T23 
                 5.77300 
               
               
                   
                 f1/f3 
                 0.24837 
                 V1 − V2 
                 32.1 
               
               
                   
                 f1/f23 
                 0.63936 
                 V1 − V3 
                 32.1 
               
               
                   
                   
               
             
          
         
       
     
         [0084]    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. 
         [0085]    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. 
         [0086]    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. 
         [0087]    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.