Abstract:
An image lens system includes a first lens group that includes a first and a second lens, a movable second lens group that includes a third and a fourth lens, and a third lens group that includes a fifth lens. The image lens system satisfies the formulas: 2.1≦Lw/(a*Y)&lt;2.5; 1.9≦|Fp|/F 1 |≦2.2; and 0.6≦|Fp 2 /F 2 |≦0.7, where “Lw” represents the overall length of the image lens system in the wide angle state, “a” represents the ratio of the effective focal length of the image lens system in the telephoto state to that in the wide angle state, “Y” represents the maximum height of image that the image lens system generates, “Fp 1 ” and “Fp 2 ” represents the effective focal lengths of the second and the fourth lenses, “F 1 ” and “F 2 ” represents the effective focal lengths of the first and the second lens groups.

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure relates to image lens systems and, particularly, to an image lens system with a high resolution and a short overall length. 
     2. Description of Related Art 
     In order to obtain a clear image and reduce the size of a camera module, an image lens system of the camera module with high resolution and short overall length are needed. But there is a contradiction between a short overall length of the image lens system and a high resolution of the image lens system. For example, reducing the number of lenses usually shortens the overall length of the image lens system, but resolution of the image lens system will suffer. Conversely, increasing the number of lenses of the image lens system usually increases resolution of the image lens system, but the overall length of the image lens system is increased. 
     Therefore, it is desirable to provide an image lens system, which satisfies the above-mentioned needs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present disclosure should be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. 
         FIG. 1  is a schematic view of an image lens system when the image lens system is in a wide angle state, in accordance with an embodiment. 
         FIG. 2  is a schematic view of the image lens system of  FIG. 1  in a telephoto state. 
         FIGS. 3-6  are graphs respectively showing spherical aberration, field curvature, distortion, and lateral chromatic aberration occurring in the image lens system of  FIG. 1  when the image lens system is in the wide angle state. 
         FIGS. 7-10  are graphs respectively showing spherical aberration, field curvature, distortion, and lateral chromatic aberration occurring in the image lens system of  FIG. 1  when the image lens system is in the telephoto state. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will now be described in detail with reference to the drawings. 
     Referring to  FIGS. 1 and 2 , an image lens system  10 , according to an exemplary embodiment, is shown. The image lens system  10  includes, in order from the object side to the image side thereof, a first lens group  100  with negative refraction power, a second lens group  200  with positive refraction power, and a third lens group  300  with positive refraction power. An imaging plane  130  is positioned at the image side of the image lens system  10 . When capturing an image, incident light enters the image lens system  10 , transmitting through the first lens group  100 , the second lens group  200 , the third lens group  300 , and finally is focused onto the imaging plane  130  where an image sensor (not shown) such as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) is located. 
     The first lens group  100  and the third lens group  300  are fixed. The second lens group  200  is movable. Thereby, the effective focal length of the image lens system  10  can be adjusted by moving the second lens group  200  along the optical axis of the image lens system  10 . In particular, the distance between the first lens group  100  and the second lens group  200  along the optical axis of the image lens system  10  increases when the image lens system  10  switches from a wide angle state to a telephoto state. 
     In this embodiment, the first lens group  100  includes, in the order from the object side to the image side of the image lens system  10 , a first lens  102  with negative refraction power and a second lens  104  with positive refraction power. The first lens  102  includes a first surface  51  with negative refraction power, facing the object side, and a second surface S 2  with positive refraction power, facing the image side. The second lens  104  includes a third surface S 3  with positive refraction power, facing the object side, and a fourth surface S 4  with negative refraction power, facing the image side. 
     The second lens group  200  includes, in the order from the object side to the image side of the image lens system  10 , a third lens  202  with positive refraction power and a fourth lens  204  with positive refraction power. The third lens  202  includes a fifth surface S 5  with positive refraction power, facing the object side, and a sixth surface S 6  with positive refraction power, facing the image side. The fourth lens  204  includes a seventh surface S 7  with positive refraction power, facing the object side, and a eighth surface S 8  with negative refraction power, facing the image side. 
     The third lens group  300  includes a fifth lens  303  with positive refraction power. The fifth lens  303  includes a ninth surface S 9  with positive refraction power, facing the object side, and a tenth surface S 10  with positive refraction power, facing the image side. The first lens group  100 , the second lens group  200 , and the third lens group  300  are all made of glass. 
     To ensure that the image lens system  10  have short overall length and high resolution, the image lens system  10  is set to satisfy the following formulas:
 
2.1 ≦Lw /( a*Y )&lt;2.5;  (1)
 
1.9 ≦|Fp 1 /F 1|≦2.2;  (2)
 
0.6 ≦|Fp 2 /F 2|≦0.7.
 
     In the formula (1), “Lw” is the overall length of the image lens system  10 , that is, the distance along the optical axis of the image lens system  10  from the first surface S 1  of the first lens  102  to the imaging plane  130  when it is in the wide angle state, “a” is the zoom ratio of the image lens system  10  which is the ratio of the effective focal length of the image lens system  10  in the telephoto state to that is in the wide angle state, “Y” is the maximum height of the image the image lens system  10  generates, “*” means multiply. When the value of “Lw/(a*Y)” is too low, the aberration is too difficult to fixed. On the contrary, when the value of the “Lw/(a*Y)” is too high, the overall length of the image system  10  is too long. Thus, the formula (1) ensures that the aberration of the image system  10  can be fixed, while the overall length of the image system  10  is short. 
     In the formula (2), “Fp 1 ” is the effective focal length of the second lens  104 . “F 1 ” is the effective focal length of the first lens group  100 . When the value of “|Fp 1 /F 1 |” is too low, there will be serious field curvature of the image lens system  10 . Conversely, when the value of the “|Fp 1 /F 1 |” is too high, there will be serious astigmatism of the image lens system  10 , which adversely affects the resolution of the image lens system  10 . Therefore, the formula (2) keeps the field curvature and the astigmatism in a suitable range. 
     In the formula (3), “Fp 2 ” is the effective focal length of the fourth lens  204 , and “F 2 ” is the effective focal length of the second lens group  200 . When the value of “|Fp 2 /F 2 |” is too low, there will be serious astigmatism of the image lens system  10 . When the value of “|Fp 2 /F 2 |” is too high, there will be serious field curvature and chromatic aberration of the image lens system  10 . Thus, the formula (3) favorably limits the field curvature and chromatic aberration the of the image lens system  10  in a suitable range. 
     To balance the overall length, the zoom ratio and the resolution of the image lens system  10 , the image lens system  10  further satisfies the formulas:
 
0.65 &lt;M 2 /Ft&lt; 0.76.  (4)
 
0.25 &lt;L 12 t/Ft&lt; 0.3.  (5)
 
     wherein “M 2 ” is the maximum movement distant of the second lens group  200  along the optical axis when the image lens system  10  moves from the wide angle state to the telephoto state. “L 12   t ” is the distance along the optical axis between the first surface S 1  and the fifth surface S 5  when the image lens system  10  is in the telephoto state. In addition, “Ft” is the effective focal length of the image lens system  10  in the telephoto state. 
     To improve the image quality of the image lens system  10 , the image lens system  10  further includes an aperture stop  400  arranged between the second lens group  200  and the third lens group  300 , a filter  150  next to the third lens group  300 , and a glass cover  160  next to the imaging plane  130 . In one embodiment, the aperture stop  400  is arranged on the eighth surface S 8  of the second lens group  200  and moves with the second lens group  200 . The aperture stop  400  is configured for adjusting light flux from the second lens group  200  to the third lens group  300 , thus to facilitate uniform light transmission to correct coma aberrations of the image lens system  10 . The filter  150  includes an eleventh surface S 11  facing the object side and a twelfth surface S 12  facing the image side. The glass cover  160  includes a thirteenth surface S 13  facing the object side and a fourteenth surface S 14  facing the image side. 
     Detailed examples of the image lens system  10  are given below. But it should be noted that the image lens system  10  is not limited to these examples. Listed below are the symbols used in the detailed examples:
     R: radius of curvature;   D: distance between two adjacent lens surfaces along the optical axis of the image lens system  10 , wherein the unit is millimeter;   Nd: refractive index of lens with respect to the d light;   v: Abbe constant;   Conic: coin constant.   

     Table 1 shows the lens data of the present example. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Lens surfaces 
                 Type 
                 R 
                 D 
                 nd 
                 Vd 
                 Conic 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 S1 
                 Spherical 
                 114.4 
                 0.7 
                 1.7725 
                 49.62  
                 — 
               
               
                 S2 
                 Spherical 
                 5.52 
                 1.613 
                 — 
                 — 
                 — 
               
               
                 S3 
                 Aspheric 
                 10.86 
                 1.32 
                 1.8466 
                 23.78  
                 1.891247 
               
               
                 S4 
                 Aspheric 
                 22.199 
                 12.428 
                 — 
                 — 
                 1.371508 
               
               
                 S5 
                 Aspheric 
                 3.45 
                 1.1417 
                 1.7433 
                 49.325 
                 −3.38292 
               
               
                 S6 
                 Aspheric 
                 −29.0738 
                 0.066 
                 — 
                 — 
                 −147.4572 
               
               
                 S7 
                 Spherical 
                 5.51 
                 0.989 
                 1.9228 
                 20.884 
                 — 
               
               
                 S8 
                 Spherical 
                 2.42 
                 0.558 
                 — 
                 — 
                 — 
               
               
                 Aperture stop 
                 — 
                 Infinity 
                 3.36 
                 — 
                 — 
                 — 
               
               
                 S9 
                 Spherical 
                 23.815 
                 1.3667 
                 1.6967 
                 56.42  
                 — 
               
               
                 S10 
                 Spherical 
                 −14.8019 
                 1.952 
                 — 
                 — 
                 — 
               
               
                 S11 
                 — 
                 Infinity 
                 0.3 
                 1.5168 
                 64.167 
                 — 
               
               
                 S12 
                 — 
                 Infinity 
                 0.3 
                 — 
                 — 
                 — 
               
               
                 S13 
                 — 
                 Infinity 
                 0.5 
                 1.5168 
                 64.167 
                 — 
               
               
                 S14 
                 — 
                 Infinity 
                 0.4 
                 — 
                 — 
                 — 
               
               
                 Imaging plane 
                 — 
                 Infinity 
                 — 
                 — 
                 — 
                 — 
               
               
                   
               
             
          
         
       
     
     The third surface S 3 , the fourth surface S 4 , the fifth surface S 5 , and the sixth surface are aspheric surfaces. The aspheric surfaces are shaped according to the formula. 
             x   =         ch   2       1   +       1   -       (     k   +   1     )     ⁢     c   2     ⁢     h   2               +     ∑     Aih   i               
wherein “h” is a height from the optical axis of the zoom lens system  100  to the aspheric surface, “c” is a vertex curvature, “k” is a conic constant, and “Ai” is i-th order correction coefficients of the aspheric surfaces. Table 2 lists the aspheric coefficients of the lens surfaces of the second lens  104  and the third lens  202 .
 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 S3 
                 S4 
                 S5 
                 S6 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 A4 
                 −5.50292627E−04 
                 −7.79519566E−04 
                 7.61616608E−03 
                 1.79622017E−04 
               
               
                 A6 
                 −3.90081893E−05 
                 −3.17852908E−05 
                 −5.01392006E−04 
                 5.94625391E−04 
               
               
                 A8 
                 2.22517662E−06 
                 2.57527394E−06 
                 −4.92792716E−05 
                 −6.00809753E−04 
               
               
                 A10 
                 −3.29480912E−08 
                 −1.09806363E−07 
                 4.20706002E−05 
                 2.90545574E−04 
               
               
                 A12 
                 −8.88537388E−11 
                 6.05255361E−09 
                 −1.02950127E−05 
                 −7.29529150E−05 
               
               
                 A14 
                 1.18244619E−10 
                 −1.85306142E−10 
                 1.42880302E−06 
                 9.23481619E−06 
               
               
                 A16 
                 −5.75716349E−12 
                 −6.48843465E−13 
                 −1.01939687E−07 
                 −4.81524134E−07 
               
               
                   
               
             
          
         
       
     
     Table 3 lists the distance between each lens group when the image lens  10  is at the wide angle state and the telephoto state. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 state 
                 f 
                 D4 
                 D9 
                 D11 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Wide angle state 
                 4.2 
                 12.428 
                 3.3613 
                 1.9525 
               
               
                   
                 Telephoto state 
                 15.7 
                 0.6815 
                 14.3095 
                 1.439 
               
               
                   
                   
               
             
          
         
       
     
     Wherein “f” is the effective focal length of the image lens system  10 , “D 7 ” is the distance on the optical axis between the first lens group  100  and the second lens group  200 , that is the distance on the optical axis between the fourth surface S 4  and the fifth surface S 5 , “D 9 ” is the distance on the optical axis between the second lens group  200  and the third lens group  300 , that is the distance on the optical axis between the aperture stop  400  and the ninth surface S 9 , “D 11 ” is the distance on the optical axis between the third lens group  300  and the filter  150 , that is the distance on the optical axis between the fifth lens  303  and the filter  150 . 
     The spherical aberration, field curvature, distortion, and lateral chromatic aberration of the image lens system  10  when it is in the wide angle state and the telephoto state is shown in  FIGS. 3-10 , wherein the curves “a”, “b”, “c”, “d”, and “e” respectively represent the lights of wavelengths of 436 nm, 486 nm, 546 nm, 588 nm, and 656 nm. Referring to  FIGS. 3 and 7 , the spherical aberration of the image lens system  10  is between −0.2 mm to 0.2 mm. Referring to  FIGS. 4 and 8 , the tangential field curvature and the sagittal field curvature of the image lens system  10  is between −0.2 mm to 0.2 mm. Referring to  FIGS. 5 and 9 , the distortion of the image lens system  10  is between −14% to 14%. Referring to  FIGS. 6 and 10 , the lateral chromatic aberration of the image lens system  10  is between −5 μm˜5 μm. 
     It will be understood that the above particular embodiments is shown and described by way of illustration only. The principles and the features of the present disclosure may be employed in various and numerous embodiment thereof without departing from the scope of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.