Zoom lens
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a zoom lens adapted for use in a compact camera. 
     2. Related Background Art 
     Zoom lenses are recently employed even in compact cameras with lens shutters, and the zoom lens adapted for such use is disclosed for example in the U.S. Pat. No. 4,720,179. 
     However the zoom lens disclosed in said patent has as many as eight components and is difficult to supply inexpensively to the users. 
     For this reason, zoom lenses with fewer components are disclosed for example in the Japanese Laid-open Patents Sho 62-56917 and Sho 62-284319, and the U.S. Pat. Nos. 4,772,106 and 4,682,860. 
     Among these, the Japanese Laid-open Patent Sho 62-56917 proposes the use of an aspherical lens while the Japanese Laid-open Patent Sho 62-284319 proposes the use of a gradient-index lens, but the use of such elements is undesirable because such elements are more expensive than the ordinary spherical lenses. 
     Also, the U.S. Pat. Nos. 4,772,106 and 4,682,860 provide zoom lenses with 5 to 7 elements, but the zoom ratio of these zoom lenses is limited to 1.5 times. 
     SUMMARY OF THE INVENTION 
     In consideration of the foregoing, the object of the present invention is to provide an inexpensive zoom lens of high performance, which is compact in shape with about six components, and still has a zoom ratio of 1.6 times or higher. 
     The foregoing object can be attained, according to the present invention, by a zoom lens provided with a first lens group G1 of a positive refractive power and a second lens group G2 of a negative refractive power, satisfying following conditions (a) to (c), and adapted to achieve zooming function by varying the air gap between said lens groups, wherein (a) said first lens group G1 comprises a positive meniscus lens component L11 with a convex face directed to the object side, a biconcave lens component L12, a biconvex lens component L13, and a positive lens component L14; (b) said second lens group G2 comprises a positive meniscus lens component L21 with a convex face directed to the image side, and a negative meniscus lens component L22 with a concave face directed to the object side; and (c) the above-mentioned lens components satisfy following five conditions: ##EQU1## wherein: K: d 12  ·n 12  +d 13  ·n 13  +d 14  ·n 14  +D 12  +D 13   
     d 12  : axial thickness of biconcave lens component L12; 
     d 13  : axial thickness of biconvex lens component L13; 
     d 14  : axial thickness of positive lens component L14; 
     n 12  : refractive index of biconcave lens component L12; 
     n 13  : refractive index of biconvex lens component L13; 
     n 14  : refractive index of positive lens component L14; 
     D 12  : axial air gap between biconcave lens component L12 and biconvex lens component L13; 
     D 13  : axial air gap between the biconvex lens component L13 and positive lens component L14; 
     f w  : focal length of the entire system at the widest angle side; 
     r a  : radius of curvature of a face, closest to the object side, of the positive meniscus lens component L21 in the second lens group; 
     r b  : radius of curvature of a face, closest to the image side, of the positive meniscus lens component L21 in the second lens group; 
     D 21  : axial air gap between the positive meniscus lens component l21 and the negative meniscus lens component L22 in the second lens group; 
     r c  : radius of curvature of a face, closest to the object side, of the negative meniscus lens component L22 in the second lens group; 
     r d  : radius of curvature of a face, closest to the image side, of the negative meniscus lens component L22 in the second lens group; 
     n 21  : refractive index of the positive meniscus lens component L21 in the second lens group; and 
     n 22  : refractive index of the negative meniscus lens component L22 in the second lens group. 
     The specific features of the present invention is as follows. 
     In a two-group zoom lens with positive and negative groups, there generally increases the positive distortion aberration at the wide angle side if the zoom ratio is extended in the wide angle side. Also a positive distortion aberration tends to appear in the second lens group if the second lens group G2 is composed of as little as two lenses, as in the zoom lens of the present invention. In order to correct such distortion aberration, a negative distortion aberration has to be generated in the first lens group G1. 
     For this purpose, it is effective to suitably shape the lens components distant from the diaphragm and generating particularly large distortion aberrations namely the positive lens component L11 closest to the object and the negative lens component L12 positioned second, of the first lens group. 
     In the zoom lens of the present invention, therefore, the positive lens component L11 positioned closest to the object in the first lens group is composed of a meniscus shape with a convex face directed toward the object side, in order to minimize the positive distortion aberration generated by converging function of said component. 
     Also the negative lens component L12 positioned second from the object side in the first lens group is the only origin of the negative distortion aberration, by the diverging function. For effectively generating said negative distortion aberration, said negative lens component L12 has a biconcave form, thereby increasing the incident angle of the off-axis oblique ray at the face at the object side of said lens component, and decreasing the emergent angle of the off-axis oblique ray at the face at the image side. 
     Thus the zoom lens of the present invention generates a negative distortion aberration in the first lens group G1 and can extremely effectively compensate the positive distortion aberration generated in the second lens group G2. 
     As explained above, the second lens group G2 of negative refractive power generates a positive distortion aberration. In order to minimize said positive distortion aberration thereby facilitating the correction thereof, the negative lens component L22 in said lens group has a meniscus form with a concave face directed to the object side. 
     As explained above, the zoom lens of the present invention has a structure advantageous for the correction of the distortion aberration. 
     Also the zoom lens of the present invention tends to generate a positive spherical aberration due to the negative refractive power of the second lens group G2, and said spherical aberration tends to increase in the positive direction when the zooming operation is conducted from the wide angle side to the telephoto side. Thus, in order to prevent the variation in spherical aberration resulting from zooming, it is necessary to intentionally generate a negative spherical aberration in the positive lens component L21 positioned at the object side in the second lens group G2, thereby satisfactorily correct the spherical aberration within said second lens group G2. 
     A biconvex positive lens component L21 cannot fully correct the positive spherical aberration generated in the negative meniscus lens component L22. In the zoom lens of the present invention, therefore, said positive lens component L21 is given a meniscus form iwth a convex face directed to the image side, thereby generating a larger negative spherical aberration and satisfactorily correcting the variation in the spherical aberration resulting from zooming operation. Besides, if a diaphragm is provided in the space between the first and second lens group, the structure is advantageous for the correction of astigmatism and coma because the faces of the positive meniscus lens L21, with a convex directed to the image side, are positioned concentrically with respect to the position of said diaphragm. 
     In the following explained are the conditions (1) to (5) of the zoom lens of the present invention. 
     The condition (1) defines the appropriate optical path length when the light, entering the biconcave lens component L12 of the first lens group G1, passes through the biconvex lens component L13 and the positive lens component L14. In a two-group zoom lens with positive and negative lens groups, the diaphragm is generally positioned at the image side of the first lens group G1. In the zoom lens of the present invention, a negative distortion aberration is generated in the object side face, distanct from the diaphragm, of the biconcave lens component L12 of the first lens group, in order to correct the aforementioned distortion aberration. Thus, said negative distortion aberration increases when the optical distance, or optical path length, of said face from the diaphragm increases. Consequently the condition (1) defines the appropriate optical path length. An area above the upper limit of said condition (1) is undesirable as the first lens group G1 becomes large to increase the dimension of the entire lens system. On the other hand, below the lower limit of said condition (1), it becomes difficult to satisfactorily correct the positive distortion aberration generated in the second lens group G2. 
     The condition (2) defines the optimum shape of the positive meniscus lens component L21, with convex faces directed to the image side, in the second group. Outside the upper and lower limits, the correction of spherical aberration becomes difficult. 
     When the distance between the positive meniscus lens component L21 and the negative meniscus lens component L22 constituting the second lens group G2 is increased, a parallel light beam from infinite distance, entering the positive meniscus lens component L21 is subjected to the converging action thereof, thus reducing the beam diameter entering the negative meniscus lens component L22. Since the diverging function of said negative meniscus lens component L22 on siad light lbeam becomes weaker, it is possible to reduce the positive spherical aberration generated in the negative meniscus lens component L22. Thus the condition (3) defines the appropriate air gap between the positive meniscus lens component L21 and the negative meniscus lens component L22 in the second lens group. Above the upepr limit of said condition (3), the second lens group G2 becomes larger, and a high zoom ratio cannot be obtained, since it becomes difficult to maintain an appropriate distance between the first lens group G1 and the second lens group G2. It also becomes difficult to secure a sufficiently large back-focus distance at the wide angle side. On the other hand, below the lower limit of said condition, the spherical aberration is excessively corrected. 
     The condition (4) defines the optimum shape of the negative meniscus lens L22, in the second lens group, with concave faces directed to the object side. Outside the upper and lower limits of said condition (4), the spherical aberration and the distortion aberration become difficult to correct. 
     The condition (5) defines the appropriate difference in refractive indexes of the positive meniscus lens component L21 and the negative meniscus lens component L22 in the second lens group. Above the upper limit of said condition (5), the Petzvar&#39;s sum increases negatively whereby the curvature of image plane becomes difficult to correct. On the other hand, below the lower limit of said condition, the positive meniscus lens component L21 of the second lens group generates an undesirably large coma aberrration. 
     In the two-group zoom lens with positive and negative groups such as the zoom lens of the present invention, the distance between the first and second lens groups G1, G2 is largest while the back-focus distance is shortest at the wide angle end, and vice versa at the telephoto end. Thus, in such zoom lens, once the focal lengths of the first and second lens groups are respectrively determined, the focal length of the entire system at the telephoto end can be determined within a range not causing mechanical interference of the lens groups. In such structure, the distance between the first and second lens groups has to made larger in order to extend the zoom ratio at the telephotoside. However, if said distance is selected large, it becomes difficult to secure a sufficient back-focus distance at the wide angle end. 
     Consequently, in the zoom lens of the present invention, the power of the positive lens component L14 is selected larger than the synthesized power of three lens components L11-L13 positioned at the object side of the first-mentioned lens component L14, whereby the rear principal point of the first lens group G1 is positioned closer to the image and a sufficiently large distance is secured between the first and second lens groups. It is therefore rendered possible to satisfactorily extend the zoom ratio at the telphoto side and to secure a sufficiently large back-focus distance at the wide angle end. 
     For securely achieving these results, there is preferred a structure satisfying an additional condition: 
     
         0.7&lt;f.sub.L14 /f.sub.1 &lt;1.30                               (6) 
    
     wherein: 
     f L14  : focal length of positive lens component L14 positioned closest to the image in the first lens group G1; and 
     f 1  : focal length of the first lens group G1. 
     Above the upper limit of the condition (6), the distance between the first and second lens groups becomes smaller, whereby it becomes difficult to extend the zoom ratio at the telephotoside. On the other hand, below the lower limit, the refractive power of the positive lens component L14 increases, whereby the spherical aberration becomes difficult to correct. 
     Also in the zoom lens of the present invention, the second lens group G2 has a two-lens structure composed of a positive lens component and a negative lens component, thereby enabling satisfactory correction of the spherical aberration and the chromatic aberration from the wide angle end to the telephoto end and also enabling inexpensive manufacture. Also in order to prevent ghost image resulting from the reflection between the lens face closest to the image and the film surface, positive and negative lens components are arranged in succession from the object side in the second lens group G2. Consequently the zoom lens of the present invention can secure a sufficiently large back-focus distance at the wide angle end. 
     In the above-mentioned zoom lens, the focusing operation can be achieved by the movement of the first lens group G1 toward the object, and the focusing mechanism can thus be simplified. However the focusing may also be achieved for example by dividing the positive lens component L14, closest to the image side, of the first lens group into two portions, and moving the portion at the object side toward the object, instead of moving the entire lens group G1. Such focusing method allows to minimize the variation in the astigmatism, thereby realizing better focusing at a shorter distance. 
     In such case, there is preferred a structure satisfying a condition: 
     
         3&lt;f.sub.b /f.sub.a                                         ( 7) 
    
     wherein: 
     f a  : focal length of a positive lens La positioned at the object side in the positive lens component L14; and 
     f b  : focal length of a positive lens Lb positioned at the image side in the positive lens component L14. 
     Said condition (7) defines the appropriate power distribution in the divided lenses. Outside said range, the curvature of image plane becomes excessively large in the focusing at a short distance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of the lens structure of a first embodiment of the present invention; 
     FIG. 2 is a view of the lens structure of a second embodiment; 
     FIG. 3 is a view of the lens structure of a third embodifment; 
     FIG. 4 is a view of the lens structure of a fourth embodiment; 
     FIG. 5 is a view of the lens structure of a fifth embodiment; 
     FIG. 6 is a view of the lens structure of a sixth embodiment; 
     FIG. 7 is a view of the lens structure of a seventh embodiment; 
     FIG. 8 is a view of the lens structure of an eighth embodiment; and 
     FIG. 9 is a view of the lens structure of a ninth embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now the zoom lens of the present invention will be clarified in detail by 1st to 9th embodiment thereof respectively shown in FIGS. 1 to 9, wherein the zoom lens comprises a first lens group G1 and a second lens group G2, in which said first lens group G1 comprises a positive meniscus lens component L11, a biconcave lens component L12, a biconvex lens component L13 and a positive lens component L14, while said second lens group G2 comprises a positive meniscus lens component L21 and a negative meniscus lens component L22. 
     The 1st to 6th embodiments shown in FIGS. 1 to 6 have a similar lens structure. In the 1st and 6th embodiments, the biconvex lens L13 in the first lens group is composed of a thick lens. In the 2nd to 5th embodiments, the biconcave lens L12 in the first lens group is composied of a thick lens. 
     In the 7th embodiment shown in FIG. 7, the biconcave lens L12 and the biconvex lens L13 are adhered together. In the 8th embodiment shown in FIG. 8, the positive lens L14 in the first lens group is divided into a positive lens La and another positive lens Lb. In the 9th embodiment shown in FIG. 9, the biconcave lens L12 and the biconvex lens L13 are adhered together. 
     The zooming operation in said embodiments is conducted, as indicated by arrows in the drawings, from the wide angle end to the telephoto end, by movements of the first lens group G1 and the second lens group G2 toward the object side with gradually decreasing distance therebetween. 
     The parameters of the above-mentioned embodiments are shown in Tabs. 1 to 9, in which the numbers at left indicate the sequential order of lens faces from the object side; wherein: 
     r: radius of curvature of lens face; 
     d: distance of lens faces; 
     n: refractive index for d-line (λ=587.6 nm); 
     ν: Abbe&#39;s number for d-line (λ=587.6 nm); 
     2ω: imaging angle. 
     
                       TABLE 1                                                     
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(1st embodiment)                                                          
f: 36.0-68.8, F-number: 4.1-7.6                                           
2ω: 61.0-35.1°                                               
r            d            ν     n                                      
______________________________________                                    
1         16.372     3.00       60.7   1.56384                            
2         37.477     2.00                                                 
3         -20.721    1.50       39.6   1.80454                            
4         16.348     0.45                                                 
5         18.352     7.55       60.3   1.51835                            
6         -16.096    2.20                                                 
7         23.475     4.50       54.6   1.51454                            
8         -40.863    (variable)                                           
9         -22.036    1.90       25.5   1.80458                            
10        -17.207    5.77                                                 
11        -13.148    1.30       35.7   1.90265                            
12        -67.882    (Bf)                                                 
f          36.0006   50.0013    68.8022                                   
d8         11.3199   6.4937     3.1026                                    
Bf         9.8700    23.2300    41.1707                                   
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                       TABLE 2                                                     
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(2nd embodiment)                                                          
f: 36.0-68.0, F-number: 4.1-7.5                                           
2ω: 61.0-35.6°                                               
r            d            ν     n                                      
______________________________________                                    
1         14.139     2.50       69.9   1.51860                            
2         25.439     2.50                                                 
3         -17.871    4.50       33.9   1.80384                            
4         21.446     0.40                                                 
5         26.319     4.00       49.0   1.53172                            
6         -14.601    0.50                                                 
7         20.589     4.50       45.9   1.54814                            
8         -56.295    (variable)                                           
9         -17.775    1.90       25.8   1.78472                            
10        -14.986    5.80                                                 
11        -12.810    1.30       35.7   1.90265                            
12        -46.351    (Bf)                                                 
f          36.0007   50.0002    68.0003                                   
d8         11.5569   6.3876     2.8688                                    
Bf         9.5907    23.6029    41.6193                                   
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                       TABLE 3                                                     
______________________________________                                    
(3rd embodiment)                                                          
f: 36.1-68.1, F-number: 4.1-7.5,                                          
2ω: 60.6-35.5°                                               
r            d            ν     n                                      
______________________________________                                    
1         14.870     2.50       69.9   1.51860                            
2         27.442     2.50                                                 
3         -17.471    6.00       40.9   1.79631                            
4         27.982     0.30                                                 
5         45.246     3.00       69.9   1.51860                            
6         -14.504    0.20                                                 
7         19.187     2.00       54.6   1.51454                            
8         -50.673    (variable)                                           
9         -18.644    1.90       25.5   1.80458                            
10        -15.153    5.00                                                 
11        -12.749    1.30       40.9   1.79631                            
12        -56.845    (Bf)                                                 
f          36.0672   49.9999    68.0792                                   
d8         14.2920   8.3620     4.2854                                    
Bf         9.5060    24.4895    43.9323                                   
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                       TABLE 4                                                     
______________________________________                                    
(4th embodiment)                                                          
f: 36.0-68.0, F-number: 4.1-7.5                                           
2ω: 60.1-35.5°                                               
r            d            ν     n                                      
______________________________________                                    
1         14.564     2.50       59.0   1.51823                            
2         27.044     2.50                                                 
3         -17.273    5.50       39.6   1.80454                            
4         27.373     0.25                                                 
5         41.082     3.00       60.3   1.51835                            
6         -14.174    0.20                                                 
7         19.085     2.00       64.1   1.51680                            
8         -52.653    (variable)                                           
9         -17.928    1.90       33.9   1.80384                            
10        -14.698    5.00                                                 
11        -12.286    1.30       52.3   1.74810                            
12        -60.199    (Bf)                                                 
f          36.0006   50.0008    68.0007                                   
d8         14.0178   8.0638     4.0111                                    
Bf         9.4214    24.4674    43.8121                                   
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                       TABLE 5                                                     
______________________________________                                    
(5th embodiment)                                                          
f: 36.0-68.0, F-number: 4.1-7.5,                                          
2ω: 60.1-35.4°                                               
r            d            ν     n                                      
______________________________________                                    
1         15.632     2.50       64.1   1.51680                            
2         29.556     2.50                                                 
3         -17.066    6.30       40.9   1.79631                            
4         25.246     0.30                                                 
5         31.544     3.00       69.9   1.51860                            
6         -14.845    0.20                                                 
7         20.696     2.00       54.6   1.51454                            
8         -43.209    (variable)                                           
9         -19.192    1.90       27.6   1.74077                            
10        -15.925    6.00                                                 
11        -13.265    1.30       46.5   1.80411                            
12        -66.996    (Bf)                                                 
f          36.0072   50.0000    67.9987                                   
d8         14.2159   8.6809     4.9109                                    
Bf         8.8173    22.8068    40.8013                                   
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                       TABLE 6                                                     
______________________________________                                    
(6th embodiment)                                                          
f: 38.8-58.8, F-number: 4.0-6.0,                                          
2ω: 57.3-40.9°                                               
r             d           ν     n                                      
______________________________________                                    
1          16.868     2.80      47.1   1.67003                            
2          48.371     1.30                                                
3          -34.269    1.70      38.0   1.72342                            
4          15.684     0.50                                                
5          33.614     5.45      60.3   1.62041                            
6          -115.527   2.70                                                
7          35.897     3.40      58.5   1.65160                            
8          -22.975    (variable)                                          
9          -29.506    2.90      31.7   1.75692                            
10         -16.357    2.95                                                
11         -13.182    1.50      37.2   1.83400                            
12         -69.316    (Bf)                                                
f           38.8002   45.0002   58.8000                                   
d8          14.0398   10.2296   4.6335                                    
Bf          12.2169   20.1273   37.7341                                   
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                       TABLE 7                                                     
______________________________________                                    
(7th embodiment)                                                          
f: 36.0-68.0, F-number: 4.1-7.5,                                          
2ω: 60.2-35.6°                                               
r            d            ν     n                                      
______________________________________                                    
1         15.283     2.50       57.0   1.62280                            
2         23.015     2.50                                                 
3         -17.507    6.00       39.6   1.80454                            
4         18.125     3.80       54.6   1.51454                            
5         -14.547    0.20                                                 
6         18.547     2.00       64.1   1.51680                            
7         -53.257    (variable)                                           
8         -22.375    1.90       25.5   1.80458                            
9         -15.874    4.00                                                 
10        -12.436    1.30       40.9   1.79631                            
11        -74.835    (Bf)                                                 
f          36.0007   50.0009    68.0011                                   
d7         15.1131   9.1591     5.1064                                    
Bf         9.8849    24.9310    44.2758                                   
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                       TABLE 8                                                     
______________________________________                                    
(8th embodiment)                                                          
f: 36.0-68.0, F-number: 4.1-7.5,                                          
2ω: 60.1-35.6°                                               
r             d           ν     n                                      
______________________________________                                    
1          15.021     2.50      69.9   1.51860                            
2          28.267     2.50                                                
3          -18.935    4.50      39.6   1.80454                            
4          29.135     0.40                                                
5          43.318     4.00      54.6   1.51454                            
6          -15.806    0.50                                                
7          21.293     2.00      69.9   1.51860                            
8          -79.469    1.41                                                
9          119.060    1.20      64.1   1.51680                            
10         -322.377   (variable)                                          
11         -20.493    1.90      33.9   1.80384                            
12         -15.110    4.00                                                
13         -12.120    1.30      44.7   1.80218                            
14         -59.650    (Bf)                                                
f           36.0006   50.0007   68.0012                                   
d10         12.8795   6.9255    2.8727                                    
Bf          9.6744    24.7203   44.0655                                   
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                       TABLE 9                                                     
______________________________________                                    
(9th embodiment)                                                          
f: 36.1-68.1, F-number: 4.1-7.5,                                          
2ω: 60.6-35.5°                                               
r             d           ν     n                                      
______________________________________                                    
1          13.892     2.50      69.9   1.51860                            
2          22.716     2.50                                                
3          -17.043    5.50      40.9   1.79631                            
4          18.350     3.80      60.3   1.51835                            
5          -13.767    0.20                                                
6          20.018     2.00      54.0   1.61720                            
7          -149.137   (variable)                                          
8          -18.644    1.90      25.5   1.80458                            
9          -15.153    5.00                                                
10         -12.749    1.30      40.9   1.79631                            
11         -56.845    (Bf)                                                
F           36.0696   49.9990   68.0808                                   
d7          14.2920   8.3630    4.2854                                    
Bf          9.5042    24.4825   43.9258                                   
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     Conditions of the foregoing embodiments are sumamrized in Tab. 10: 
     
                       TABLE 10                                                    
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(Comparisons of conditions)                                               
 No.                                                                      
       ##STR1##                                                           
              Q                                                           
                        ##STR2##                                          
                             R     n.sub.21 -n.sub.22                     
                                         ##STR3##                         
                                              ##STR4##                    
______________________________________                                    
1     0.66   -8.1      0.160                                              
                            1.48  -0.098                                  
                                        1.16                              
2     0.61   -11.7     0.161                                              
                            1.76  -0.118                                  
                                        1.09                              
3     0.52   -9.7      0.139                                              
                            1.58  0.008 1.02                              
4     0.50   -10.1     0.139                                              
                            1.51  0.056 1.03                              
5     0.54   -10.7     0.167                                              
                            1.49  -0.063                                  
                                        1.03                              
6     0.53   -3.5      0.076                                              
                            1.47  -0.077                                  
                                        0.76                              
7     0.55   -5.9      0.111                                              
                            1.40  0.008 1.01                              
8     0.59   -6.6      0.111                                              
                            1.51  0.002 1.04 5.17                         
9     0.53   -9.7      0.139                                              
                            1.58  0.008 1.08                              
______________________________________                                    
 wherein:                                                                 
 ##STR5##                                                                 
 
    
     The diaphragm S in the 1st to 7th and 9th embodiments is positioned in the air gap between the first lens group G1 and the second lens group G2. The faces of the positive meniscus lens L21, positioned closest to the object, in the second lens group are concave to said diaphragm and convex to the image, and are therefore advantageous in correcting the astigmatism and coma aberrations. In these embodiments, the focusing operation is conducted by moving the first lens group G1, positioned at the object side with respect to said diaphragm S, toward the object side. 
     On the other hand, in the 8th embodiment, the diaphragm S is positioned in a split gap obtained by dividing the positive lens L14 of the first lens group G1, and the focusing in said embodiment is conducted by moving the lens, positioned at the object side with respect to said diaphragm, toward the object side. Also this embodiment satisfactorily reduces the variation in astigmatic aberration in the focusing at a short distance, thereby achieving high focusing performance. 
     Thus the foregoing embodiments provide a compact zoom lens which has a relatively large zoom ratio and excellent focusing performance from the wide angle end to the telephoto end while maintaining an inexpensive compact structure with a limited number of lenses.