Abstract:
A front zoom system and a rear zoom system are coupled in said order from an object side, wherein said rear zoom system comprises a fixed positive lens group, a negative compensator lens group in which its first plane has its convex plane facing an object side and its last plane has its concave plane facing an image side, a negative variator lens group in which the lens group itself is virtually achromated, and a fixed relay lens group, being positioned in the order given from an object side. While the magnification variation range is enlarged by consecutively performing the zooming operation of the front zoom system and the zooming operation of the rear zoom system, aberrations at that time are satisfactorily corrected. The focal distance of the variator lens group is made short in comparison with that of the compensator lens group, thus the amount of shifting of this lens group is reduced for making the rear zoom system compact.

Description:
BACKGROUND OF INVENTION 
     The present invention is related to a zoom lens in which the magnification variation range as employed in an ordinarily used zoom lens is further enlarged and at the same time the magnification variation with an enlarged ranged can be consecutively done. 
     An ordinary zoom lens consists of a zoom part to determine the variation ratio of focal distance and a relay part to determine the variation range of focal distance, and has for example, zooming range of 50 mm to 500 mm. 
     However, there are such cases that zooming range of 100 mm to 1000 mm is desired during photographing, and at that time what is ordinarily done is to replace a relay part or to add a magnifying lens system in front of the zoom part or between the zoom part and the relay part. But such method has disadvantages that replacing of the relay part or mounting of the magnifying lens system takes time, and further the photographing image is cut out in a course of photographing when said parts are mounted. 
     Contrary to the above art, a technical thought that a relay part is replaced with another zoom lens so that the front zoom part with M times power and the rear zoom part with N times power are connected together to obtain a zoom lens with M× N times power has been known for example by the Japanese Utility Model Pat. No. Sho 40-2871. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to shorten the total length of a zoom lens by placing plural number of movable lens groups at a rear zoom part and the movable lens groups corrects image plane shifting at an object side and the movable lens group varys the focal distance at an image side as the lens group of divergent nature. Another object of the invention is to secure satisfactory aberration correction even when the total length is shortened. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a cross-sectional view showing a concrete example of the present invention. 
     FIGS. 2A1, 2A2, and 2A3 (collectively FIGS. 2A); FIGS. 2B1, 2B2, and 2B3) (collectively FIGS. 2B); and FIGS. 2C1, 2C2, and 2C3 (collectively FIGS. 2C) are drawings for various aberrations of example 1 of actual values according to the concrete example of FIG. 1. 
     FIGS. 3A1, 3A2 and 3A3 (collectively FIGS. 3A); FIGS. 3B1, 3B2, and 3B3 (collectively FIGS. 3B); and FIGS. 3C1, 3C2, and 3C3 (collectively FIGS. 3C) are drawings for various aberrations of example 2 of actual values. FIG. 4 is a drawing to show another example of the present invention. FIGS. 5A1, 5A2, and 5A3 (collectively FIGS. 5A); FIGS. 5B1, 5B2, and 5B3 (collectively FIGS. 5B); and FIGS. 5C1, 5C2, and 5C3 (collectively FIGS. 5C) are drawings for various aberrations of the example 3 of actual values according to FIG. 4. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Now, examples of the present invention will be explained. Here, a rear fixed relay part is made as a zoom lens system of a front diaphragm type having a diaphragm at the front part by providing plural number of divergent type lens systems which can move relatively from one direction to the other within a lens system which is equivalent to a rear fixed relay part. And of the image magnification variation of each divergent lens system itself, which is generated as a result of shifting of the lens group when the above mentioned divergent lens system is shifted from one direction to the other, the lens system with great influence over image magnification variation is made a focal distance variation lens system, while other lens systems are made an imaging plane shifting correction lens system, then in this rear zoom lens system of a front diaphragm type the lens system for correcting the imaging plane shifting is placed at a position closer to an object than that from the focal distance variation lens system. In FIG. 1, I is a front zoom part, and II is a rear zoom part and is connected to the front zoom part I. Also the front zoom part I has a convergent lens system 1, and divergent lens systems 2 and 3, while the rear zoom part II has a front fixed lens system A having a diaphragm between two positive lens groups, a lens system B for correcting imaging plane shifting, a focal distance variation lens system C and a rear fixed lens system D. Here, the front zoom part I may be of different structure than what is mentioned above. 
     In the above mentioned set-up, the focal distance variation lens system C is in itself an almost achromated divergent lens system and has at least one each of a divergent lens and a convergent lens, having at least two divergent planes and one convergent plane, wherein by making the refractive index of the convergent lens and the divergent lens more than 1.75 or by making the difference in Abbe number of the convergent lens and the divergent lens more than 15 the correction of Petzual sum, spherical aberration, coma (aberration) and distortion aberration is intended. As this focal distance variation lens system C is shifted to change its position, the amount of variation of aberration increases remarkably unless each aberration of the lens system C only is corrected to a certain satisfactory level. 
     It is desired that when the shortest focal distance of the total lens system which consists of the front zoom part I and the rear zoom part II is made f and the focal distance of the focal distance variation lens system C is made fc, the equation 
     
         0.5 f≦ |fc | 
    
     is satisfied. If the focal distances do not fall within the above mentioned range the amount of variation in aberration can not be allowed, while when the equation, 
     
         | fc| &lt; 4f 
    
     is not satisfied, the size of the rear zoom lens part II which is determined by the amount of shifting of the lens system C becomes too large to be allowed, thus it is very inconvenient in practical use. 
     Also the lens system B for correcting image plane shifting is a divergent lens system, and when the plane from which light is exited out is made to have divergent function it is advantageous for correction of spherical aberration. And when the synthesized focal distance of the lens system B for correcting imaging plane shifting is made fB, it is desired that the following equation is satisfied: 
     
         |fb| ≧ |1.5 fc| 
    
     (wherein fc is a synthesized focal distance of the focal distance varying lens system C.). When | fb|  is smaller than |1.5fc| , the amount of aberration can not be allowed. Further, the rear fixed lens system D is a convergent lens system and is for example separated into two groups of front and rear groups and it is better to use a lens with a refractive index of 1.63 or less as a convergent lens consisting of the lens system, and to use a lens with refractive index of 1.75 or larger as a divergent lens. And by providing a divergent plane having a curvature center at an object side in the front group and at an imaging plane side in the rear group, correction of Petsval sum, spherical aberration, coma (aberration) and distortion aberration can be done advantageously. 
     Also the front fixed lens system A has its focal distance so determined that an imaging point by the front zoom part I takes a position suitable as an object point of the lens system B for correcting imaging plane shifting, and it is advantageous in many cases to secure balancing of the aberration correction of the total lens system consisting of the front zoom part I and the rear zoom part II in this front fixed lens system A. However in the case when the aberration correction of the front zoom part I is satisfactorily done and the imaging point by the front zoom part I is at a position suitable as an object point of B, the above mentioned front fixed lens system A may be omitted. 
     When the elements of the rear zoom lens part are selected as in the embodiment of FIG. 1, an axial luminous flux passes the front zoom part I and the front fixed lens system A. The flux is incident upon the lens system B for correction of imaging plane shifting in a state of convergent light and will be projected from the same with its state of convergence somewhat weakened then will be incident into the focal distance variation lens system C then will be projected from the lens system C in a state of divergent light. Therefore as the lens systems B and C are within convergent luminous flux the height from the optical axis in the case when the light beam passes through these lens systems to the light beam can be lowered, thus the effective diameter of lens can be made small. That is according to Matsui&#39;s theme on aberration, tertial spherical aberration is in proportion to the cube of diameter while coma (aberration) is proportional to the square of the diameter. From this when the effective diameter of lens is small, even if the focal distance of lens is shortened, aberration can be satisfactorily corrected. Also it is convenient for reducing the length of the rear zoom lens part II to shorten the focal distance of the focal distance variation lens C and to reduce the amount of shifting, and if the focal distance of the lens system C becomes long the incident height of oblique luminous flux becomes high, not only increasing the diameter of the lens system D but increasing the total length, thus very disadvantageous. 
     As has been explained above the present invention is quite useful in that the replacement of the rear fixed relay part and the mounting of the converter, etc. are not necessary and it becomes possible to consecutively enlarge the magnification variation range of the front zoom part using the rear fixed relay part as the zoom lens system of front diaphragm type, furthermore the rear zoom part comes in a very compact size. 
     Now actual values on concrete examples will be shown and satisfactorily corrected aberration will be shown in FIG. 2A, FIG. 2B and FIG. 2C. 
     
                       Example 1______________________________________of Actual Values:Focal distance: 24 to 800Zooming ratio : 1 : 33.3Relative aperture: 1 : 1.8 to 1: 4.5(shortest focal distance to longest focal distance)Effective picture size: 16 φ   r        d        n          ν______________________________________1         1086.39                8        1.7552   27.52         283.68                1.483         280.91                23.31    1.51633  64.14         -1173.26                0.25         289.546                17.62    1.51633  64.16         1566.37                0.27         278.268                13.27    1.51633  64.18         921.892( * 0.5517 - 183.958 - 228.885)9         364.93                3        1.816    46.810        70.69                911        -87                2.52     1.816    46.812        96.245                6        1.92286  20.913        -788.25( * 235.681 - 29.5934 - 7.3484 )14        -101.8                3.02     1.7859   44.215        100.08                10       1.80518  25.416        -3088( * 5.9945 - 28.6778 - 5.9945) 17       -2040                6        1.48749  70.118        -104.18                0.219        261.69                6.5      1.48749  70.120        -200.33                3.51121        234.581                12.782   1.60311  60.722        -88.1214                3.5      1.80518  25.423        -289.98                0.224        79.5158                3        1.7552   27.525        54.7653                10.473   1.62041  60.326        431.943( * 13.1102 - 17.6795 - 16.5754)27        138.145                5.957    1.71736  29.528        -633.921                2.5      1.72     50.329        59.18( * 7.1707 - 26.2014 - 43.7055 )30        123.27                4.772    1.92286  21.331        -382.77                2.5      1.816    46.832        69.0452                6.81533        -74.2236                2.5      1.816    46.834        413.701( * 42.8562 - 19.2562 - 2.8562 ) 35      -600.211                    7.736  1.60311  60.7 36      -109.249                    0.2 37      146.829                    11.823 1.60311  60.7 38      -139.73                    3      1.80518  25.4 39      1373.05                    0.2 40      129.318                    7.872  1.60311  60.7 41      1539.52                    29.808 42      110.432                    3      1.71736  29.5 43      70.8992                    6.566 44      162.808                    6.778  1.51633  64.1 45      -360.162                    0.2 46      79.4534                    7.974  1.51633  64.1 47      347.566                    20 48      ∞                    69.2   1.51633  64.1 49      ∞______________________________________ The values with * marks show the cases of shortest, middle and longest focal distances. The asterisk marks   show a color resolving prism system But, r is a radius of curvature, d is a plane separation or lens thickness, n is refractive index and ν is dispersion. 
    
     
                       Example 2______________________________________of Actual Values:Focal distance:     24 to 801.5Zooming ratio:      1 : 33.3Relative aperture:  1 : 1.8 to 1 : 4.5(shortest focal distanceto longest focal distance)Effective plane size:               16 φr             d         n            μ______________________________________ 1   1086.39                1.7552     27.5             8 2   283.68             1.48 3   280.91                 1.51633    64.1             23.31 4   -1173.26             0.2 5   289.546                1.51633    64.1             17.62 6   1566.37             0.2 7   278.268                1.51633    64.1             13.27 8   921.892( 0.5517 - 183.9578 - 228.8848 ) 9   364.93                 1.816      46.8             310   70.69             911   -87                    1.816      46.8             2.5212   96.245                 1.92286    20.9             613   -788.25( 235.6815 - 29.5934 - 7.3484 )14   -101.8                 1.7859     44.2             3.0215   100.08                 1.80518    25.4             1016   -3088( 5.9945 - 28.6778 - 5.9945 )17   -2040                  1.48749    70.1             618   -104.18             0.219   261.69                 1.48749    70.1             6.520   -200.33             4.7821   202.224                1.60311    60.7             13.3722   -97.715                1.80518    25.4             3.523   -786.13             0.224   73.177                 1.7552     27.5             325   52.795                 1.62041    60.3             10.4326   325.572( 10.0755 - 14.3473 - 13.5601 )27   12.893                 1.71736    29.5             6.5928   -326.227               1.72       50.3             2.529   52.351( 5.9359 - 39.0442 - 62.4514 )30   103.145                1.92286    21.3             5.7531   676.097                1.816      46.8             2.532   67.592             7.0633   ;31 87.405             1.816      46.8             2.534   -949.076( 62 - 24.6 - 2 )35   -521.814               1.60311    60.7             7.3936   -106.58             0.237   154.335                1.60311    60.7             12.7238   -137.301               1.80518    25.4             339   1437.934             0.240   129.132                1.60311    60.7             8.5541   8613.412             30.0142   92.371                 1.71736    29.5             343   68.499             8.4344   319.795                1.51633    64.1             3.7745   396.717             0.246   70.644                 1.51633    64.1             7.9447   348.921             2348   ∝               1.51633    64.1             69.249   ∝______________________________________ 
    
     The state of various aberrations for the above example 2 of actual values is shown in FIG. 3A, FIG. 3B and FIG. 3C. 
     
                       Example 3______________________________________of Actual Values:(According to Example shown in FIG. 4)Focal distance:     24 to 798.16Zooming ratio:      1 : 33.3Relative aperture:  1 : 1.8 to 1 : 45(shortest focal distanceto longest focal distance)Effective plane diameter:               16 φr             d         n            μ______________________________________ 1   1086.39                1.7552     27.5             8 2   283.68             1.48      1.51633    64.1 3   280.91             23.31 4   -1173             0.2       1.51633    64.1 5   289.546             17.62 6   1566.37             0.2       1.51633    64.1 7   278.268             13.27 8   921.723                1.816      46.8( 0.551 - 183.9571 - 228.884 ) 9   364.93             310   70.69             911   -87                    1.816      46.8             2.5212   96.245                 1.92286    20.9             613   -788.25( 235.6815 - 29.5934 - 7.3484 )14   -101.8                 1.7859     44.2             3.0215   100.08                 1.80518    25.4             1016   -3088( 5.9945 - 28.6778 - 5.9945 )17   -2040                  1.48749    70.1             618   -104.18             0.219   261.69                 1.48749    70.1             6.520   -200.33             9.1121   148.764             11.38     1.64       60.222   -96.819                1.80518    25.4             3.523   -786.13             0.224   63.7                   1.80518    25.4             325   52.23                  1.67       57.4             11.0426   634.933( 20.5044 - 25.3528 - 23.0322 )27   6990.557               1.71736    29.5             3.3128   8734.535               1.72       50.3             2.529   141.047( 4.1573 - 4.7089 - 12.4295 )30   235.509                1.92286    20.9             4.0631   -132.187               1.816      46.8             2.532   39.589             8.9333   -44.352                1.816      46.8             2.534   176.636             935   -59.367                1.816      46.8             2.536   -2642.876( 12.8 - 7.4 - 2 )37   - 753.452              1.60311    60.7             15.4638   -49.472             0.239   133.874                1.60311    60.7             11.0640   -287.402               1.80518    25.4             3.041   521.457             0.242   135.472                1.60311    60.7             7.8443   -26689.125             35.7344   163.529                1.71736    29.5             345   68.35             8.2446   149.667                1.51633    64.1             12.8247   -151.699             0.248   58.946                 1.51633    64.1             15.8449   362.778             2350   ∞                1.51633    64.1             69.251   ∞______________________________________ 
    
     The state of various aberrations for the above example of actual figures is shown in FIG. 5A, FIG. 5B, FIG. 5C.