Abstract:
The present invention provides a micro-projection lens including first lens group, a second lens group, and a third lens group arranged in sequence along an optical axis from a screen side to a light modulator side. The first lens group has positive refractive power and includes at least an aspheric lens. The second lens group has negative refractive power and includes at least a glass tablet. The third lens group has positive refractive power and includes at least an aspheric lens. Therefore, the micro-projection lens of the present invention has a small size and high optical performance.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a lens, and more particularly to a micro-projection lens. 
         [0003]    2. Description of the Related Art 
         [0004]    As the progress of technology, projectors are more and more popular in conference, video conference or watching movies. For portability of the projector, a micro-projector, which is small and light, had been presented in market. A lens for the micro-projector, it has to be smaller and lighter than the conventional projection lens, and furthermore, it must have high resolution and high contract to provide high optical performance. Therefore, small size and high optical performance are two important facts for lens of the micro-projector. 
         [0005]    Conventional lenses for the micro-projector usually have a plurality of lens groups to obtain high optical performance. Some of them have more than ten lenses, however, this kind of lens has high optical performance, but is big and heavy. It is a trade-off between the size and optical performance in the lens for micro-projector. 
       SUMMARY OF THE INVENTION 
       [0006]    The primary objective of the present invention is to provide a micro-projection lens, which has a small size and a high optical performance. 
         [0007]    According to the objective of the present invention, the present invention provides a micro-projection lens including first lens group, a second lens group, and a third lens group arranged in sequence along an optical axis from a screen side to a light modulator side. 
         [0008]    In order to have a great image quality, the first lens group has positive refractive power and includes at least an aspheric lens. 
         [0009]    In order to raise imaging quality, the second lens group has negative refractive power and includes at least a glass tablet. 
         [0010]    In order to reduce chromatic aberration, the third lens group has positive refractive power and includes at least an aspheric lens. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a sketch diagram of the arrangement of the lenses of a first preferred embodiment of the present invention; 
           [0012]      FIG. 2  is a sketch diagram of light path of the first preferred embodiment of the present invention; 
           [0013]      FIG. 3A  is a field curvature diagram and a distortion diagram of the first preferred embodiment of the present invention; 
           [0014]      FIG. 3B  is a through focus MTF diagram of the first preferred embodiment of the present invention; 
           [0015]      FIG. 3C  is a spatial frequency MTF diagram of the first preferred embodiment of the present invention; 
           [0016]      FIG. 4  is a sketch diagram of the arrangement of the lenses of a second preferred embodiment of the present invention; 
           [0017]      FIG. 5  is a sketch diagram of light path of the second preferred embodiment of the present invention; 
           [0018]      FIG. 6A  is a field curvature diagram and a distortion diagram of the second preferred embodiment of the present invention; 
           [0019]      FIG. 6B  is a through focus MTF diagram of the second preferred embodiment of the present invention; 
           [0020]      FIG. 6C  is a spatial frequency MTF diagram of the second preferred embodiment of the present invention; 
           [0021]      FIG. 7  is a sketch diagram of the arrangement of the lenses of a third preferred embodiment of the present invention; 
           [0022]      FIG. 8  is a sketch diagram of light path of the third preferred embodiment of the present invention; 
           [0023]      FIG. 9A  is a field curvature diagram and a distortion diagram of the third preferred embodiment of the present invention; 
           [0024]      FIG. 9B  is a through focus MTF diagram of the third preferred embodiment of the present invention; and 
           [0025]      FIG. 9C  is a spatial frequency MTF diagram of the third preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 1  is the arrangement of a micro-projection lens  1  of the first preferred embodiment of the present invention, and  FIG. 2  is the light path of  FIG. 1 . As shown in  FIG. 1  and  FIG. 2 , the micro-projection lens  1  of the first preferred embodiment of the present invention includes: 
         [0027]    The micro-projection lens  1  of the first preferred embodiment of the present includes, along an optical axis Z from a screen side to a light modulator (DMD) side, a first lens group G 11 , an aperture STO 1 , a second lens group G 12 , and a third lens group G 13 . 
         [0028]    The first lens group G 11  has positive refractive power and includes a first lens L 11  and a second lens L 12 . The first lens L 11  is a plastic, aspheric, and meniscus lens with negative refractive power. The first lens L 11  has a convex surface S 1  facing the screen side and a concave surface S 2  facing the DMD side. The convex surface S 1  and the concave surface S 2  are aspheric. The second lens L 12  is a plastic, aspheric, and meniscus lens with positive refractive power. The second lens L 12  has a convex surface S 3  facing the screen side and a concave surface S 4  facing the DMD side. The convex surface S 3  and the concave surface S 4  are aspheric. The second lens L 12  leads the positive refractive power of the first lens group G 11 . The first lens L 11  and the second lens L 12  further have the following condition to improve image quality and reduce chromatic aberration: 
         [0000]      0.4 &lt;f 2/ F 12&lt;0.08 
         [0029]    wherein: 
         [0030]    f2: effective focus length of the second lens L 12 ; and 
         [0031]    F12: composite focus length of the first lens L 11  and the second lens L 12 . 
         [0032]    The second lens group G 12  has negative refractive power and includes a third lens L 13  and a fourth lens L 14 . The third lens L 13  is a glass lens with negative refractive power, and the fourth lens L 14  is a glass lens with positive refractive power. The third lens L 13  leads the negative refractive power of the second lens group G 12 . The third lens L 13  and the fourth lens L 14  are bonded together to form a doublet L 134  with negative refractive power. The doublet L 134  has the following condition to reduce chromatic aberration and beam expansion: 
         [0000]      0.1 &lt;f 3 /F 34&lt;0.5 
         [0033]    wherein: 
         [0034]    f3: effective focus length of the third lens L 13 ; and 
         [0035]    F34: composite focus length of the doublet L 134 . 
         [0036]    The third lens group G 13  includes a fifth lens L 15 , which is a plastic lens with positive refractive power, and both surfaces S 9 , S 10  of which are aspheric. The third lens group G 13  may enhance imaging of the first lens group G 11  and correct field curvature and astigmatism to raise the image quality of the micro-projection lens  1  of the present invention. 
         [0037]    In addition, the micro-projection lens  1  is further provided with a color filter CF 1  and a beam splitter BS 1  between the third lens group B 13  and the screen side. They are common in the prior art, so we do not describe the detail here. 
         [0038]    Table 1 shows focus length (F), F-number (Fno), radius of curvature of the lens at the optical axis (R), thickness of the lens at the optical axis (T), refractive index (Nd), and the Abbe number (Vd) of the micro-projection lens  1  of the first preferred embodiment: 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 F = 1 mm Fno = 1.87 
               
             
          
           
               
                   
                 Surface 
                 R(mm) 
                 T(mm) 
                 Nd 
                 Vd 
                 Note 
               
               
                   
                   
               
             
          
           
               
                   
                 OBJ 
                 ∞ 
                 85 
                   
                   
                   
               
               
                   
                 S1 
                 1.3988 
                 0.0505 
                 1.5346 
                 56.0722 
                 L11 
               
               
                   
                 S2 
                 0.7772 
                 0.0137 
               
               
                   
                 S3 
                 0.4796 
                 0.1273 
                 1.6142 
                 25.5765 
                 L12 
               
               
                   
                 S4 
                 1.2118 
                 0.0275 
               
               
                   
                 S5 
                 0 
                 0.281 
                   
                   
                 STO1 
               
               
                   
                 S6 
                 −0.3314 
                 0.1403 
                 1.8081 
                 22.7608 
                 L134 
               
               
                   
                 S7 
                 5.8649 
                 0.392 
                 1.8348 
                 42.7137 
               
               
                   
                 S8 
                 −0.6727 
                 0.0137 
               
               
                   
                 S9 
                 1.0354 
                 0.5072 
                 1.5346 
                 56.0722 
                 L15 
               
               
                   
                 S10 
                 −1.3539 
                 0.0549 
               
               
                   
                 S11 
                 ∞ 
                 0.0549 
                 1.5069 
                 63.1283 
                 CF1 
               
               
                   
                 S12 
                 ∞ 
                 0.0412 
               
               
                   
                 S13 
                 ∞ 
                 1.0711 
                 1.544 
                 56.2 
                 BS1 
               
               
                   
                 S14 
                 ∞ 
                 0 
               
               
                   
                   
               
             
          
         
       
     
         [0039]    In the present embodiment, the depths of aspheric surfaces S 1 , S 2 , S 3 , S 4 , S 9 , and S 10  may be obtained by the following equation: 
         [0000]    
       
         
           
             z 
             = 
             
               
                 
                   ch 
                   2 
                 
                 
                   1 
                   + 
                   
                     
                       [ 
                       
                         1 
                         - 
                         
                           
                             ( 
                             
                               k 
                               + 
                               1 
                             
                             ) 
                           
                            
                           
                             c 
                             2 
                           
                            
                           
                             h 
                             2 
                           
                         
                       
                       ] 
                     
                     
                       1 
                       2 
                     
                   
                 
               
               + 
               
                 Ah 
                 4 
               
               + 
               
                 Bh 
                 6 
               
               + 
               
                 Ch 
                 8 
               
               + 
               
                 Dh 
                 10 
               
               + 
               
                 Eh 
                 12 
               
               + 
               
                 Fh 
                 14 
               
               + 
               
                 Gh 
                 16 
               
             
           
         
       
     
         [0040]    Wherein: 
         [0041]    z: depth of aspheric concave surface; 
         [0042]    c: reciprocal of radius of curvature; 
         [0043]    h: radius of aperture of surface; 
         [0044]    k: conic constant; and 
         [0045]    A˜G: coefficient of the radius of aperture of surface. 
         [0046]    Table 2 shows the conic constants k of the aspheric surfaces and the coefficients A˜G of the radius of aperture of surface h: 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Surface 
                 S1 
                 S2 
                 S3 
                 S4 
                 S9 
                 S10 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 K 
                 18.06013 
                 5.887988 
                 −4.91669 
                 −0.40475 
                 0.631234 
                 −0.87562 
               
               
                 A 
                 4.422165 
                 −0.53822 
                 0.847186 
                 −1.61333 
                 −0.21466 
                 0.336144 
               
               
                 B 
                 −48.115 
                 −15.6236 
                 0 
                 0 
                 0.279976 
                 0.026312 
               
               
                 C 
                 102.096 
                 −103.981 
                 0 
                 0 
                 −0.4814 
                 1.023267 
               
               
                 D 
                 796.3909 
                 −4448.82 
                 0 
                 0 
                 −0.88204 
                 −2.81254 
               
               
                 E 
                 −18767.3 
                 22847.17 
                 0 
                 0 
                 3.414232 
                 2.365793 
               
               
                 F 
                 19959.34 
                 365518.4 
                 0 
                 0 
                 −2.38517 
                 3.899506 
               
               
                 G 
                 −506023 
                 −9192814 
                 0 
                 0 
                 0.631234 
                 −0.97562 
               
               
                   
               
             
          
         
       
     
         [0047]    With the arrangement of the lenses and the aperture, the micro-projection lens  1  of the first preferred embodiment is small in size and has a good image quality. The detail data are shown in  FIG. 3A  to  FIG. 3C . 
         [0048]      FIG. 3A  is a field curvature diagram and a distortion diagram of the first preferred embodiment of the present invention;  FIG. 3B  is a through focus MTF diagram of the first preferred embodiment of the present invention; and  FIG. 3C  is a spatial frequency MTF diagram of the first preferred embodiment of the present invention. In  FIG. 3A , the maximum field curvature is between 0.08 mm and −0.04 mm, and the distortion is under 2%. In  FIG. 3B , it shows that the micro-projection lens  1  of the first preferred embodiment has a good resolution from any field of view. In  FIG. 3C  the spatial frequency MTF still is greater than 50% in 66 lp/mm. The results show the resolution of the micro-projection lens  1  of the first embodiment of the present invention is qualified. 
         [0049]    As shown in  FIG. 4  and  FIG. 5 , a micro-projection lens  2  of the second preferred embodiment of the present invention includes, along an optical axis Z from a screen side to a light modulator (DMD) side, a first lens group G 21 , an aperture STO 2 , a second lens group G 22 , a third lens group G 23 , a color filter CF 2 , and a beam splitter BS 2 , in which the first lens group G 21  has positive refractive power, the second lens group G 22  has negative refractive power, and the third lens group G 23  has positive refractive power. 
         [0050]    The first lens group G 21  includes a first lens L 21  and a second lens L 22 . The first lens L 21  is a plastic, aspheric, and meniscus lens with negative refractive power. The first lens L 21  has a convex surface S 1  and a concave surface S 2 , and both of them are aspheric. The second lens L 22  is a plastic, aspheric, and meniscus lens with positive refractive power. The second lens L 12  has a convex surface S 32  and a concave surface S 4 , and both of them are aspheric. The second lens L 12  leads the positive refractive power of the first lens group G 11 . The first lens L 11  and the second lens L 12  further have the following condition to improve image quality and reduce chromatic aberration: 
         [0000]      0.4 &lt;f 2 /F 12&lt;0.95 
         [0051]    wherein: 
         [0052]    f2: effective focus length of the second lens L 22 ; and 
         [0053]    F12: composite focus length of the first lens L 21  and the second lens L 22 . 
         [0054]    The second lens group G 22  includes a third lens L 23  and a fourth lens L 24 . The third lens L 23  is a glass lens with negative refractive power, and the fourth lens L 24  is a glass lens with positive refractive power. The third lens L 23  and the fourth lens L 24  are bonded together to form a doublet L 234  with negative refractive power. The doublet L 234  has the following condition to reduce chromatic aberration and beam expansion: 
         [0000]      0.1 &lt;f 3 /F 34&lt;0.5 
         [0055]    wherein: 
         [0056]    f3: effective focus length of the third lens L 23 ; and 
         [0057]    F34: composite focus length of the doublet L 234 . 
         [0058]    The third lens group G 23  includes a fifth lens L 25 , which is a plastic lens with positive refractive power, and both surfaces S 9 , S 10  of which are aspheric. The third lens group G 23  may enhance imaging of the first lens group G 21  and correct field curvature and astigmatism. 
         [0059]    Table 3 shows focus length (F), F-number (Fno), radius of curvature of the lens at the optical axis (R), thickness of the lens at the optical axis (T), refractive index (Nd), and the Abbe number (Vd) of the micro-projection lens  2  of the second preferred embodiment: 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 F = 1 mm Fno = 1.87 
               
             
          
           
               
                 Surface 
                 R(mm) 
                 T(mm) 
                 Nd 
                 Vd 
                 Note 
               
               
                   
               
             
          
           
               
                 OBJ 
                 ∞ 
                 123 
                   
                   
                   
               
               
                 S1 
                 1.0402 
                 0.0959 
                 1.5312 
                 56.0438 
                 L21 
               
               
                 S2 
                 0.6758 
                 0.0137 
               
               
                 S3 
                 0.4829 
                 0.1534 
                 1.607 
                 27 
                 L22 
               
               
                 S4 
                 2.2343 
                 0.022 
               
               
                 S5 
                 0 
                 0.2074 
                   
                   
                 STO2 
               
               
                 S6 
                 −0.286 
                 0.0959 
                 1.8467 
                 23.7779 
                 L234 
               
               
                 S7 
                 2.3327 
                 0.3749 
                 1.8348 
                 42.7137 
               
               
                 S8 
                 −0.6664 
                 0.0137 
               
               
                 S9 
                 1.1673 
                 0.53 
                 1.5312 
                 56.0438 
                 L25 
               
               
                 S10 
                 −0.867 
                 0.0548 
               
               
                 S11 
                 0 
                 0.0959 
                 1.5069 
                 29.0329 
                 CF2 
               
               
                 S12 
                 0 
                 0.0411 
               
               
                 S13 
                 0 
                 1.0685 
                 1.544 
                 56.2 
                 BS2 
               
               
                 S14 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
         [0060]    In the present embodiment, the depths of aspheric surfaces S 1 , S 2 , S 3 , S 4 , S 9 , and S 10  may be obtained by the following equation: 
         [0000]    
       
         
           
             z 
             = 
             
               
                 
                   ch 
                   2 
                 
                 
                   1 
                   + 
                   
                     
                       [ 
                       
                         1 
                         - 
                         
                           
                             ( 
                             
                               k 
                               + 
                               1 
                             
                             ) 
                           
                            
                           
                             c 
                             2 
                           
                            
                           
                             h 
                             2 
                           
                         
                       
                       ] 
                     
                     
                       1 
                       2 
                     
                   
                 
               
               + 
               
                 Ah 
                 4 
               
               + 
               
                 Bh 
                 6 
               
               + 
               
                 Ch 
                 8 
               
               + 
               
                 Dh 
                 10 
               
               + 
               
                 Eh 
                 12 
               
               + 
               
                 Fh 
                 14 
               
               + 
               
                 Gh 
                 16 
               
             
           
         
       
     
         [0061]    Wherein: 
         [0062]    z: depth of aspheric concave surface; 
         [0063]    c: reciprocal of radius of curvature; 
         [0064]    h: radius of aperture of surface; 
         [0065]    k: conic constant; and 
         [0066]    A˜G: coefficient of the radius of aperture of surface. 
         [0067]    Table 4 shows the conic constants k of the aspheric surfaces and the coefficients A˜G of the radius of aperture of surface h: 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Surface 
                 S1 
                 S2 
                 S3 
                 S4 
                 S9 
                 S10 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 K 
                 −3.56434 
                 −12.0594 
                 −5.5006 
                 4.107109 
                 −2.64746 
                 0.100194 
               
               
                 A 
                 0.213774 
                 −5.33006 
                 −2.15296 
                 −1.18515 
                 −0.04917 
                 0.510103 
               
               
                 B 
                 −12.8265 
                 18.03895 
                 33.12787 
                 −14.3793 
                 0.393039 
                 0.090766 
               
               
                 C 
                 14.72801 
                 283.9151 
                 501.4091 
                 341.818 
                 −0.67881 
                 0.603814 
               
               
                 D 
                 −1270.91 
                 −2346.93 
                 −2496.55 
                 −4770.77 
                 0.274208 
                 −0.99677 
               
               
                 E 
                 19424.1 
                 8416.695 
                 34986.49 
                 41239.42 
                 1.429255 
                 1.971666 
               
               
                 F 
                 −39771.3 
                 135996.8 
                 −116968 
                 120959.7 
                 −1.65382 
                 0.164762 
               
               
                 G 
                 3E−07 
                 6E−07 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
         [0068]    With the arrangement of the lenses and the aperture, the micro-projection lens  2  of the second preferred embodiment is small in size and has a good image quality. The detail data are shown in  FIG. 6A  to  FIG. 6C . 
         [0069]      FIG. 6A  is a field curvature diagram and a distortion diagram of the second preferred embodiment of the present invention;  FIG. 6B  is a through focus MTF diagram of the second preferred embodiment of the present invention; and  FIG. 6C  is a spatial frequency MTF diagram of the second preferred embodiment of the present invention. In  FIG. 6A , the maximum field curvature is between 0.05 mm and −0.03 mm, and the distortion is under 2%. In  FIG. 6B , it shows that the micro-projection lens  1  of the first preferred embodiment has a good resolution from any field of view. In  FIG. 6C  the spatial frequency MTF still is greater than 40% in 66 lp/mm. The results show the resolution of the micro-projection lens  2  of the second embodiment of the present invention is qualified. 
         [0070]    As shown in  FIG. 7  and  FIG. 8 , a micro-projection lens  3  of the third preferred embodiment of the present invention includes, along an optical axis Z from a screen side to a light modulator (DMD) side, a first lens group G 31 , an aperture STO 3 , a second lens group G 32 , a third lens group G 33 , a color filter CF 3 , and a beam splitter BS 3 , in which the first lens group G 31  has positive refractive power, the second lens group G 32  has negative refractive power, and the third lens group G 33  has positive refractive power. 
         [0071]    The first lens group G 31  includes a first lens L 31  and a second lens L 32 . The first lens L 31  is a plastic, aspheric, and meniscus lens with negative refractive power, and the second lens L 32  is a plastic, aspheric, and meniscus lens with positive refractive power. The first lens L 31  and the second lens L 32  have a convex surface S 1 , S 3  and a concave surface S 2 , S 4  respectively, and all of them are aspheric. The first lens L 31  and the second lens L 32  further have the following condition to improve image quality and reduce chromatic aberration: 
         [0000]      0.4 &lt;f 2 /F 12&lt;0.95 
         [0072]    wherein: 
         [0073]    f2: effective focus length of the second lens L 32 ; and 
         [0074]    F12: composite focus length of the first lens L 31  and the second lens L 32 . 
         [0075]    The second lens group G 32  includes a third lens L 33  and a fourth lens L 34 . The third lens L 33  is a glass lens with negative refractive power, and the fourth lens L 34  is a glass lens with positive refractive power. The third lens L 33  and the fourth lens L 34  are bonded together to form a doublet L 334 . The doublet L 334  has the following condition to reduce chromatic aberration and beam expansion: 
         [0000]      0.1 &lt;f 3 /F 34&lt;0.5 
         [0076]    wherein: 
         [0077]    f3: effective focus length of the third lens L 33 ; and 
         [0078]    F34: composite focus length of the doublet L 334 . 
         [0079]    The third lens group G 33  includes a fifth lens L 35 , which is a plastic lens with positive refractive power, and both surfaces S 9 , S 10  of which are aspheric. The third lens group G 33  may enhance imaging of the first lens group G 31  and correct field curvature and astigmatism. 
         [0080]    Table 5 shows focus length (F), F-number (Fno), radius of curvature of the lens at the optical axis (R), thickness of the lens at the optical axis (T), refractive index (Nd), and the Abbe number (Vd) of the micro-projection lens  3  of the third preferred embodiment: 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 F = 1 mm Fno = 1.85 
               
             
          
           
               
                 Surface 
                 R(mm) 
                 T(mm) 
                 Nd 
                 Vd 
                 Note 
               
               
                   
               
             
          
           
               
                 OBJ 
                 ∞ 
                 123 
                   
                   
                   
               
               
                 S1 
                 0.789 
                 0.0959 
                 1.5312 
                 56.0438 
                 L31 
               
               
                 S2 
                 0.5283 
                 0.0137 
               
               
                 S3 
                 0.4317 
                 0.143 
                 1.6073 
                 26.6467 
                 L32 
               
               
                 S4 
                 1.4137 
                 0.0829 
               
               
                 S5 
                 0 
                 0.1842 
                   
                   
                 STO3 
               
               
                 S6 
                 −0.2911 
                 0.0959 
                 1.8467 
                 23.7779 
                 L334 
               
               
                 S7 
                 3.4146 
                 0.3338 
                 1.7292 
                 54.68 
               
               
                 S8 
                 −0.6402 
                 0.0137 
               
               
                 S9 
                 1.5465 
                 0.5438 
                 1.7391 
                 48.5 
                 L35 
               
               
                 S10 
                 −0.9715 
                 0.0548 
               
               
                 S11 
                 0 
                 0.0959 
                 1.5069 
                 29.0329 
                 CF3 
               
               
                 S12 
                 0 
                 0.0411 
               
               
                 S13 
                 0 
                 1.0685 
                 1.544 
                 56.2 
                 BS3 
               
               
                 S14 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
         [0081]    In the present embodiment, the depths of aspheric surfaces S 1 , S 2 , S 3 , S 4 , S 9 , and S 10  may be obtained by the following equation: 
         [0000]    
       
         
           
             z 
             = 
             
               
                 
                   ch 
                   2 
                 
                 
                   1 
                   + 
                   
                     
                       [ 
                       
                         1 
                         - 
                         
                           
                             ( 
                             
                               k 
                               + 
                               1 
                             
                             ) 
                           
                            
                           
                             c 
                             2 
                           
                            
                           
                             h 
                             2 
                           
                         
                       
                       ] 
                     
                     
                       1 
                       2 
                     
                   
                 
               
               + 
               
                 Ah 
                 4 
               
               + 
               
                 Bh 
                 6 
               
               + 
               
                 Ch 
                 8 
               
               + 
               
                 Dh 
                 10 
               
               + 
               
                 Eh 
                 12 
               
               + 
               
                 Fh 
                 14 
               
               + 
               
                 Gh 
                 16 
               
             
           
         
       
     
         [0082]    Wherein: 
         [0083]    z: depth of aspheric concave surface; 
         [0084]    c: reciprocal of radius of curvature; 
         [0085]    h: radius of aperture of surface; 
         [0086]    k: conic constant; and 
         [0087]    A˜G: coefficient of the radius of aperture of surface. 
         [0088]    Table 4 shows the conic constants k of the aspheric surfaces and the coefficients A˜G of the radius of aperture of surface h: 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Surface 
                 S1 
                 S2 
                 S3 
                 S4 
                 S9 
                 S10 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 K 
                 −0.90216 
                 −6.39031 
                 −3.03047 
                 8.657106 
                 1.563867 
                 −0.94629 
               
               
                 A 
                 0.610119 
                 −3.41104 
                 −2.96236 
                 −1.14883 
                 −0.19942 
                 0.208831 
               
               
                 B 
                 −22.4022 
                 9.967173 
                 28.63137 
                 −14.7804 
                 0.208593 
                 −0.1448 
               
               
                 C 
                 76.66628 
                 7.92587 
                 12.72461 
                 731.8631 
                 −0.23694 
                 0.926912 
               
               
                 D 
                 −1034.08 
                 −1160.34 
                 −5208.74 
                 −13205 
                 −0.43429 
                 −8.52795 
               
               
                 E 
                 −15770.5 
                 30244.92 
                 8880.979 
                 33765.55 
                 11.32075 
                 3.436411 
               
               
                 F 
                 222201.5 
                 489454.2 
                 849961.4 
                 425232.8 
                 −0.99945 
                 −2.7541 
               
               
                 G 
                 −533657 
                 −3399486 
                 −6437981 
                 −1516959 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
         [0089]    With the arrangement of the lenses and the aperture, the micro-projection lens  2  of the second preferred embodiment is small in size and has a good image quality. The detail data are shown in  FIG. 9A  to  FIG. 9C . 
         [0090]      FIG. 6A  is a field curvature diagram and a distortion diagram of the third preferred embodiment of the present invention;  FIG. 9B  is a through focus MTF diagram of the third preferred embodiment of the present invention; and  FIG. 9C  is a spatial frequency MTF diagram of the third preferred embodiment of the present invention. In  FIG. 9A , the maximum field curvature is between 0.04 mm and −0.04 mm, and the distortion is under 2%. In  FIG. 9B , it shows that the micro-projection lens  1  of the first preferred embodiment has a good resolution from any field of view. In  FIG. 9C  the spatial frequency MTF still is greater than 50% in 66 lp/mm. The results show the resolution of the micro-projection lens  2  of the second embodiment of the present invention is qualified. 
         [0091]    In conclusion, the micro-projection lens of the present invention has a small size and a good image quality. It meets the requirements of the micro-projector. 
         [0092]    The description above is a few preferred embodiments of the present invention and the equivalence of the present invention is still in the scope of claim construction of the present invention.