Abstract:
This optical image enlarging variator comprises two coaxial components adapted to give from a fixed virtual image located at the rear of the front component, a fixed real image, located at the rear of the rear component; the magnification varies as a function of the relative position of the two components movable in relation to each other and to the fixed position of the diaphragm; the front component is divergent, comprises four lenses and the rear component also comprises four lenses; in one of their relative positions, g1=g2==G=1, and irrespective of the relative positions of these components the following requirements: 0.20&lt;g1&lt;1.60 and 0.25&lt;g2&lt;1.50 are met, as well as condition f2/f1&gt;1.2, wherein g1 is the image magnification produced by the front component, g2 the image magnification produced by the rear component, and G the image magnification produced by the complete device, f1 being in absolute value the focal length of the front component and f2 the focal length of the rear component.

Description:
BACKGROUND OF THE INVENTION 
     The present application is a continuation-in-part of the patent application Ser. No. 856,084 filed on Nov. 30, 1977, which is the continuation-in-part application of the U.S. patent application Ser. No. 730,712 filed on Oct. 8, 1976 and now both abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an image enlarging optical variator adapted to be integrated in a zoom system, and also, as a complement, to a zoom system equipped with this variator. The variator comprises two coaxial components adapted, from a fixed virtual image located behind the front component, to give a fixed real image located behind the rear component, the magnification of this real image varying as a function of the relative position of the two movable components of the variator. 
     A device of this character is adapted to be disposed coaxially behind a fixed convergent optical element of the zoom, this convergent element originating the virtual image to be converted by the variator according to this invention. 
     Moreover, the image obtained at the output end of the variator may be taken up by a fixed optical element located behind the variator so as to give a real final image having dimensions consistent with the relative positions of the movable component elements as mentioned hereinabove. The assembly thus formed of two fixed optical elements located on either side of the optical variator causing only by itself the enlargement variation, constitutes a so-called variable focal length or variable focus lens system or objective. 
     The choice of a variator is of primary importance when it is desired to obtain first-quality images, irrespective of the relative positions of its components. It is obvious that by properly selecting the components of the variator the nature of the fixed elements can be varied to infinity. 
     DESCRIPTION OF THE PRIOR ART 
     Various types of optical variators are known in the art. Thus, the U.S. Pat. No. 3,609,005 to Nakamura discloses a zoom lens incorporating an optical variator of which the rear component consists of the following elements: a first positive power meniscus having its concave front surface facing the object, i.e. the other movable component of the variator; two single biconvex elements: a doublet formed with a biconvex lens and a divergent meniscus. 
     SUMMARY OF THE INVENTION 
     The variator according to this invention comprises the following combination: 
     the two components are movable in relation to each other and also to the fixed position of the diaphragm; 
     the front component is divergent, comprises four lenses, i.e., in the front to rear direction: a first negative power meniscus having its convex surface at the front, a second negative power lens, third and fourth cemented lenses constituting a doublet in which the front lens is biconcave, the rear one being a positive power lens; 
     and the rear component comprises likewise four lenses of which one is a negative power lens and the others positive power lenses. 
     the two movable components of the variator have a relative position such that g1=g2=G=1, wherein g1 designates the magnification of the image which is produced by the front component, g2 the magnification of the image formed by the back component, and G the magnification of the image produced by the complete variator. 
     Therefore, there is necessarily a relative position of the two movable components of the variator in which these components produce simultaneously the &#34;1&#34; magnification, and this constitutes a fundamental optical property of the variator according to this invention. 
     According to a specific form of embodiment of the present invention, the negative power lens of the rear component is located at the front of this component. Moreover, since f1 is in absolute value the focal length of the front component and f2 the focal length of the rear component, the f2/f1 ratio should be in excess of 1.2. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1A illustrates a first form of embodiment of the optical variator according to present invention, associated with the two fixed components, namely the front and rear components of a zoom, the two movable components being each shown in their endmost position nearest to the corresponding fixed component; 
     FIG. 1B is a view similar to FIG. 1A showing the two components of the optical variator of this invention in their end positions opposite that shown in FIG. 1A, in which they are substantially coupled to each other; 
     FIG. 1C is a fragmentary view showing on a larger scale only the two groups of lenses of the variator of FIGS. 1A and 1B in a relative position intermediate the positions shown in these FIGS., so that g1=g2=G=1; 
     The groups of FIGS. 2A-2C, 3A-3C, 4A-4C, 5A-5C are views similar to FIGS. 1A to 1C, respectively, each group of FIGS. illustrating another form of embodiment of the optical variator and of the fixed components of the zoom objective to which the variator is incorporated. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The zoom objective illustrated in FIGS. 1A and 1B comprises two movable components I, II constituting the optical variator proper, and two fixed components III-IV located at the front and at the rear, respectively, of said components I and II. 
     Each component I to IV comprises the following elements numbered from left to right in the Figures, i.e. from the object to the real image given by the lens system; 
     Movable component I of the variator: a divergent meniscus R9-R10, a divergent lens R11-R12, a doublet R13-R15 consisting of a biconcave divergent lens R13-R14 and a convergent meniscus R14-R15. 
     Movable component II: a divergent meniscus R16-R17 coupled to a biconvex lens R17-R18, a convergent meniscus R19-R20 and a biconvex lens R21-R22. 
     Front fixed component III: a divergent lens R1-R2, a biconvex lens R3-R4, a convergent meniscus R5-R6 and a second convergent meniscus R7-R8. 
     Rear fixed component IV: a doublet R23-R25 similar to the doublet R13-R15, a divergent meniscus R26-R27, a convergent meniscus R28-R29 having its convex surface directed away from the object, and a doublet R30-R32 consisting of a divergent meniscus R30-R31 and of a biconvex lens R31-R32. 
     In their relative positions shown in FIG. 1A, the components I and II of the variator are in their closest positions to the fixed components III and IV, respectively. In contrast thereto, in the position shown in FIG. 1B, components I and II are as close as possible to each other and the relative positions of the two movable components I and II, which is shown in FIG. 1C, is the position in which g1=g2=G=1. 
     Outside this specific position, the movements of the two components of the device are responsive to a law such that their relative positions constantly preserve the fixity of the resultant image. In all cases the following conditions should be adhered to: 
     
         0.20&lt;g1&lt;1.60 
    
     
         0.25&lt;g2&lt;1.50 
    
     In FIG. 1C, the reference symbols R9, R10, R11, . . . designate the radii of curvature of the lenses constituting the movable components I and II to which the sign + is added when their convex surface is directed to the front and the sign - in the opposite case; reference symbols n9, n11, n13 . . . designate the refractive indices concerning each lens for the spectral line e. In this specific form of embodiment, the best results are obtained when the following requirements are met, f1 designating the focal length, bearing the sign -, of the front component: ##EQU1## 
     It is also advantageous to comply with the following requirements; ##EQU2## 
     In the form of embodiment illustrated in FIGS. 2A to 2C, the variator and the objective incorporating same have the following composition: 
     Movable component I of the variator: A first divergent meniscus R9-R10, a divergent lens R11-R12, and a doublet consisting of a divergent biconcave lens R13-R14 and of a convergent meniscus R14-R15 of which the convex surface is directed towards the object. 
     Movable component II: A divergent lens R16-R17, a biconvex lens R18-R19, a convergent meniscus R20-R21 and a biconvex lens R22-R23. 
     Front fixed component III: A divergent meniscus R1-R2, a biconvex lens R3-R4 and two convergent meniscus R5-R6 and R7-R8. 
     Rear fixed component IV: A doublet R24-R26 comprising a divergent lens R24-R25 and a convergent meniscus R25-R26 of which the convex face is directed towards the object, a divergent meniscus R27-R28, a convergent meniscus R29-R30 of which the convex surface is directed away from the object, a doublet R31-R33 comprising a divergent meniscus R31-R32 and a biconvex lens R32-R33. 
     FIG. 2C illustrates the relative positions of the movable components I and II, in which g1=g2=G=1. 
     In this exemplary form of embodiment, the best results are obtained when the following requirements are met, f1 designating the focal length, bearing the sign -, of the front component: ##EQU3## 
     It is also advantageous to adhere to the following requirements: ##EQU4## 
     Tables I and II given hereinafter correspond to FIGS. 1C and 2C, respectively, illustrating two concrete examples of devices meeting the requirements set forth in the foregoing. These Tables, in addition to the radii of curvature and refractive indices, of which the values have already been given hereinabove, display the reference symbols concerning the Abbe numbers ν, ν 1 , ν 2 , ν 3  . . . the reference symbols concerning the axial distances between one dioptre and the next dioptre: e1, e2, e3 . . . , reference h1 designating the distance between the last surface of the rear component and the position of diaphragm C, reference h2 designating the distance between the position of this diaphragm C and the position of the virtual initial image A, reference h3 designating the distance between the position of the virtual initial image A and the position of the real image B resulting from the effect produced by the device, said references h1, h2 and h3 bearing the sign + from front to rear and sign - in the opposite case. 
     
                       TABLE NO. 1______________________________________R             E          n      ne     νe______________________________________R1   ∞R2   +     95.29    )   e1   1.79  n1   1.81253                                          25.30R3   +     94.35        e2   0.64       airR4   -     215.52   )   e3   9.    n3   1.62285                                          60.11R5   +     106.99       e4   0.09       air               )   e5   5.    n5   1.62286                                          60.11R6   +     313.43R7   +     56.54        e6   0.09       air               )   e7   5.70  n7   1.62286                                          60.11R8   +     154.21                   e8   2.046      to 45.67R9   +     244.30               )   e9   1.    n9   1.79196                                          47.15R10  +     18.40R11  -     150.65       e10  6.10       air               )   e11  1.40  n11  1.79196                                          47.15R12  +     168.41R13  -     42.39        e12  2.75       airR14  +     26.77    )   e13  1.    n13  1.59129                                          60.9R15  +     413.63   )   e14  3.70  n14  1.85504                                          23.64                   e15  68.703     to 0.64R16  +     300.R17  +     25.76    )   e16  1.10  n16  1.70448                                          20.9R18  -     49.06    )   e17  5.50  n17  1.66024                                          56.9R19  +     62.44        e18  0.09       air               )   e19  2.20  n19  1.54398                                          73.1R21  +     57.59        e20  0.09       air               )   e21  2.80  n21  1.54396                                          73.1R22  -     162.60                   e22  3.262      to 27.70R23  -     25.55R24  +     20.50    )   e23  1.60  n23  1.59129                                          60.90R25  +     1845.34  )   e24  4.10  n24  1.85504                                          23.64R26  +     176.38       e25  4.80       air               )   e26  1.    n26  1.85504                                          23.64R27  +     28.71R28  -     266.17       e27  3.20       air               )   e28  3.70  n28  1.62286                                          60.11R29  -     21.38R30  +     70.48        e29  0.10       airR31  +     14.91        e30  1.30  n30  1.79213                                          25.7R32  -     66.58    )   e31  5.60  n31  1.59129                                          60.9______________________________________ 
    
     The first group of data (R1-R8, e1-e8 . . . ) hereinabove comprises the properties of the fixed front component III. The second group of data (R9-R15, e9-e14, . . . ) relates to the front movable component I. The third group of data (R16-R22, e16-e21 . . . ) relates to the rear movable component II, and the fourth group of data (R23-R32, e23-e31 . . . ) relates to the fixed back component IV, all these components being those shown in FIGS. 1A to 1C. 
     These components further comprise the following properties: 
     
         ______________________________________f1 = -16.42         h2 = -28.98f2 = 29.11          h3 = 58.86______________________________________ 
    
     The variable distances e15 and h1 are given hereinafter for five different settings. Also shown therein are the magnifications g1, g2 and G corresponding to each setting. 
     
         ______________________________________e15     h1        g1        g2      G______________________________________68.70   7.72      0.29      0.39    0.113549.65   11.08     0.41      0.50    0.204523.49   19.36     0.73      0.79    0.573811.18   25.54     1         1       10.64    32.16     1.31      1.23    1.6122______________________________________ 
    
     
                       TABLE No. 2______________________________________R                 E       n      ne    √e______________________________________R1    +     1786.                )   e1   1.90  n1   1.81253                                          25.30R2    +     97.                    e2   0.83       airR3    +     98.85                )   e3   7.20  n3   1.62286                                          60.11R4    -     353.02                    e4   0.10       airR5    +     90.79                )   e5   4.90  n5   1.62286                                          60.11R6    +     442.09                    e6   0.10       airR7    +     66.65                )   e7   5.    n7   1.62286                                          60.11R8    +     169.85                    e8   1.364      to    48.29R9    +     181.06                )   e9   1.    n9   1.79196                                          47.15R10   +     18.98                    e10  6.10       airR11   -     170.50                )   e11  1.    n11  1.79196                                          47.15R12   +     183.25                    e12  2.75       airR13   -     42.                )   e13  1.    n13  1.59129                                          60.9R14   +     26.71                )   e14  3.70  n14  1.88504                                          23.64R15   +     182.30                    e15  68.154           0.23R16   ∞                )   e16  1.    n16  1.79213                                          25.69R17   +     34.59                    e17  0.20       airR18   +     35.82                )   e18  5.70  n18  1.68092                                          55.27R19   -     46.17                    e19  0.08       airR20   +     53.50                )   e20  2.30  n20  1.62529                                          52.87R21   +     399.52                    e21  0.08       airR22   +     57.92                )   e22  3.20  n22  1.62529                                          52.87R23   -     107.48                    e23  3.783      to    24.77R24   -     25.90                )   e24  1.60  n24  1.59129                                          60.9R25   +     20.28                )   e25  4.10  n25  1.85504                                          23.64R26   +     335.34                    e26  4.60       airR27   +     271.50                )   e27  1.    n27  1.84294                                          29.97R28   +     27.77                    e28  3.20       airR29   -     188.16                )   e29  3.70  n29  1.62286                                          68.11R30   -     19.59                    e30  0.10       airR31   +     92.01                )   e31  1.30  n31  1.79213                                          25.69R32   +     14.29                )   e32  5.60  n32  1.59129                                          60.9R33   -     56.23f1 = 16.42          h2 = -23.44f2 = 26.67          h3 = 49.69______________________________________ 
    
     The above Table 2 also shows the four groups of data corresponding to the components of the variator and of the objective illustrated in FIGS. 2A to 2C of the drawings, i.e., in the proper order: the front fixed component III (R1 to R8), the front movable component I (R9 to R15), the rear movable component II (R16 to R23), the rear fixed component IV (R24 to R33). 
     The variable distances e15 and h1 are shown hereunder for five different settings. Also shown are the magnifications g1, g2 and G corresponding to each setting, respectively. 
     
         ______________________________________e15     h1        g1        g2      G______________________________________68.15   7.55      0.27      0.35    0.094048.01   10.49     0.38      0.46    0.172421.96   17.58     0.66      0.72    0.48106.30    24.93     1         1       10.23    28.54     1.18      1.14    1.3346______________________________________ 
    
     FIGS. 3A to 3C illustrate a third form of embodiment of the optical variator of this invention, together with the fixed components of the objective in which it is incorporated. 
     This objective has the following composition: 
     Front fixed component III: A divergent meniscus R1-R2, a convergent meniscus R3-R4; a divergent biconcave lens R5-R6; a doublet R7-R9 formed with a biconcave divergent lens R7-R8 and with a biconvex lens R8-R9; a biconvex lens R10-R11 and a biconvex lens R12-R13. 
     Front movable component I: A divergent meniscus R14-R15 a second divergent meniscus R16-R17, a doublet comprising a divergent biconcave lens R18-R19 and a biconvex lens R19-R20. 
     Rear movable component II: It comprises five lens instead of four as in the two first forms of embodiment described hereinabove. Among these five lenses, one is a negative power lens and the others are positive power lenses. These lenses are: a triplet R21-R24 consisting of a biconvex lens R21-R22, of a divergent biconcave lens R22-R23 and of a biconvex lens R23-R24 sticked on lens R22-R23; a convergent meniscus R25-R26 and a convergent biconvex lens R27-R28. 
     Rear fixed component IV: A triplet R29-R32 comprising a divergent biconcave lens R29-R30 sticked on a biconvex lens R30-R31 itself sticked in turn on a divergent meniscus R31-R32; a divergent meniscus R33-R34, a doublet comprising a divergent meniscus R35-R36 sticked on a biconvex lens R36-R37, and finally a doublet comprising a divergent meniscus R38-R39 and a biconvex lens R39-R40. 
     FIG. 3C illustrates a relative position of the two components of the corresponding device, wherein g1=g2=G=1. Outside this position, the two components of this device move according to a law such that their relative position constantly ensure the fixity of the final image. In all cases, the following requirements should be met for better results: 
     
         0.15&lt;g1&lt;1.9 
    
     
         0.20&lt;g2&lt;1.7 
    
     In FIG. 3C, the reference symbols R14, R15, R16 . . . designate the radii of curvature of the various lenses of the four components, said lenses bearing the sign + when their convex surfaces are directed towards the front and the sign - in the opposite case; reference symbols n14, n16, n18 . . . designate the refractive indices of each lens for the spectral line e. In this specific example, the best results are obtained when the following requirements are met, f1 designating the focal length, bearing the sign -, of the front component: ##EQU5## 
     It is also advantageous to adhere to the following conditions: ##EQU6## 
     The following Table No.3 corresponds to FIGS. 3A to 3C and illustrates a concrete example of devices meeting the above-mentioned requirements for this specific form of embodiment. This Table No.3, in addition to the radii of curvature R1, . . . and indices n . . . , gives the references concerning the Abbe numbers ν, ν 1 , ν 2 , ν 3  . . . , the references concerning the axial distances between one dioptre and the next dioptre: e1, e2, e3 . . . , the reference h1 designating the distance between the last surface of the rear component and the position of diaphragm C, reference h2 designating the distance between the position of diaphragm C and the position of the virtual initial image A, reference h3 designating the distance between the position of the virtual image A and the position of the real image B resulting from the effect of the device, reference h1, h2 and h3 bearing the sign + in the front to rear direction and - in the opposite case. 
     
                       TABLE No. 3______________________________________R                   E        n     ne    √ e______________________________________R1   +     827.54              )  e1    3.344  n1    1.6940R2   +     149.09R3   +     144.63     e2    0.202        air              )  e3    10.115 n3    1.81253                                          25.30R4   +     255.91R5   -     219.84     e4    13.697       air              )  e5    3.13   n5    1.89402                                          54.53R6   +     31315.79R7   -     566.67     e6    8.425        air              )  e7    2.642  n7    1.81253                                          25.30R8   +     183.96              )  e8    23.443 n8    1.48890                                          70.37R9   -     189.91R10  +     405.87     e9    0.202        air              )  e10   11.721 n10   1.66024                                          56.89R11  -     282.93                 e11   0.107        airR12  +     160.57              )  e12   14.066 n12   1.66024                                          56.89R13  -     1992.03                 e13   12.326       to    149.47R14  +     95.57              )  e14   2      n14   1.74794                                          44.55R15  +     37.93                 e15   10           airR16  +     421.41              )  e16   2      n16   1.74794                                          44.55R17  +     80.24                 e17   9            airR18  -     83.81              )  e18   2      n18   1.69402                                          54.33R19  +     48.67              )  e19   10     n19   1.81253                                          25.30R20  -     645.58                 e20   220.518      to    7.69R21  +     335.59              )  e21   8.33   n21   1.69380                                          53.80R22  -     181.29              )  e22   2.38   n22   1.81253                                          25.30R23  +     100.35              )  e23   15.47  n23   1.69380                                          53.80R24  -     137                 e24   0.119        airR25  +     171.40              )  e25   7.14   n25   1.69380                                          53.80R26  +     2171.53                 e26   0.119        airR27  +     182.85              )  e27   7.735  n27   1.69380                                          53.80R28  -     2667.09                 e28   11.898       to    87.57R29  -     71.52              )  e29   2.38   n29   1.69402                                          54.53R30  +     42.97              )  e30   17.85  n30   1.81253                                          25.30R31  -     230.89              )  e31   2.38   n31   1.69402                                          54.53R32  -     300.35                 e32   12.59        airR33  +     206.67              )  e33   2.499  n33   1.61930                                          44.19R34  +     96.38                 e34   6.951        airR35  +     447.20              )  e35   1.19   n35   1.73436                                          28.17R36  +     73.63              )  e36   10.71  n36   1.46619                                          65.56R37  -     72.95                 e37   0.25         airR38  +     112.18              )  e38   1.19   n38   1.81253                                          25.30R39  +     31.63              )  e39   14.244 n39   1.46619                                          65.56R40  -     57.82   f1 =-38.631       h2 =-90.88   f2 = 78.466       h3 = 183.78______________________________________ 
    
     The variable distances e20 and h1 are shown hereinafter for five different settings. Also shown are the magnifications g1, g2 and G corresponding to each setting, respectively. 
     
         ______________________________________e20     h1        g1        g2      G______________________________________220.52  4.16      0.236     0.349   0.0825138.42  18.03     0.406     0.526   0.21360.56   46.48     0.845     0.888   0.75044.70   55.24     1         1       17.69    79.84     1.473     1.313   1.935______________________________________ 
    
     FIGS. 4A to 4C illustrate another form of embodiment of the device of this invention, in which the components have the following compositions: 
     Front movable component I: a divergent meniscus R14-R15, a second divergent meniscus R16-R17, adoublet R18-R20 formed with a biconcave divergent lens R18-R19 and with a convergent lens R19-R20. 
     Rear movable component II: a biconvex lens R21-R22, a biconcave lens R23-R24, a biconvex lens R25-R26, a biconvex convergent lens R27-R28 and a convergent meniscus R29-R30. 
     Front fixed component III: a divergent meniscus R1-R2, a convergent meniscus R3-R4, a biconcave divergent lens R5-R6, a doublet OR7-R9 formed with a divergent biconcave lens R7-R8 and with a biconvex lens R8-R9; a biconvex lens R10-R11 and a biconvex lens R12-R13. 
     Rear fixed component IV: a doublet R31-R33 formed with a biconcave divergent lens R31-R32 and a convergent meniscus R32-R33, a biconcave divergent lens R34-R35 and a convergent meniscus R36-R37 having its convex surfaces directed away from the object; two convergent meniscus R38-R39 and R40-R41 having their convex surfaces directed away from the object, a doublet R42-R44 consisting of a biconvex lens R42-R43 and of a divergent meniscus R43-R44; a doublet consisting of a divergent meniscus R45-R46 of which the convex surfaces are directed towards the object, and of a biconvex lens R46-R47. 
     In this specific form of embodiment, the best results are obtained when the following requirements are met, f1 designating the focal length, affected by the sign-, of the front component: ##EQU7## 
     It is also advantageous to adhere to the following conditions: ##EQU8## 
     The following Table No. 4 corresponds to FIGS. 4A to 4C of the drawings and provides a numerical example of a device meeting the above requirements. The data are determined in the same manner as for the preceding Tables. 
     
                       TABLE No. 4______________________________________R                    E       n    ne     γ.sub.e______________________________________R1   +     626.96               )   e1   3.326 n1   1.69402                                          54.53R2   +     127.78                   e2   0.52       AIRR3   +     125.31               )   e3   11.954                              n3   1.81253                                          25.30R4   +     230.89                   e4   21.31      AIRR5   -     216.17               )   e5   3.118 n5   1.69402                                          54.53R6   +     8547.01                   e6   8.212      AIRR7   -     668.45               )   e7   2.599 n7   1.81253                                          25.30R8   +     178.67               )   e8   21.31 n8   1.48890                                          70.37R9   -     195.58                   e9   0.208      AIRR10  +     411.88               )   e10  13.513                              n10  1.84304                                          59.85R11  -     249.25                   e11  0.104      AIRR12  +     151.01               )   e12  12.474                              n12  1.64304                                          59.85R13  -     4344.02                   e13  1.753      to     154.58R14  +     95.10               )   e14  1.80  n14  1.74794                                          44.55R15  +     35.49                   e15  9          AIRR16  +     379.22               )   e16  1.80  n16  1.74794                                          44.55R17  +     72.22                   e17  8.10       AIRR18  -     74.98               )   e18  1.80  n18  1.69402                                          54.53R19  +     43.80               )   e19  9     n19  1.81253                                          25.30R20  -     569.80                   e20  235.032    to     1.08R21  +     300.30               )   e21  7.398 n21  1.64304                                          59.85R22  -     183.32                   e22  0.10       AIRR23  -     183.32               )   e23  2.17  n23  1.81253                                          25.30R24  +     117.61                   e24  0.10       AIRR25  +     117.61               )   e25  13.514                              n25  1.64304                                          59.85R26  -     115.22                   e26  0.099      AIRR27  +     146.41               )   e27  6.708 n27  1.62286                                          60.11R28  -     1375.52                   e28  0.099      AIRR29  +     142.73               )   e29  6.116 n29  1.62286                                          60.11R30  +     1089.56                   e30  12.60      to     93.73R31  -     230.95               )   e31  2.25  n31  1.69233                                          49.35R32  +     31.97               )   e32  13.50 n32  1.81253                                          25.30R33  +     196                   e33  5.625      AIRR34  -     86.81               )   e34  2.25  n34  1.70448                                          29.88R35  +     155.04                   e35  8.037      AIRR36  -     107.50               )   e36  3.60  n36  1.70586                                          40.82R37  -     72.14                   e37  45         AIRR38  -     77.49               )   e38  5.692 n38  1.46619                                          65.56R39  -     51.66                   e39  0.09       AIRR40  -     123.30               )   e40  5.692 n40  1.46619                                          65.56R41  -     57.44                   e41  0.09       AIRR42  -     2100.84               )   e42  9.54  n42  1.46619                                          65.56R43  -     36.05               )   e43  1.89  n43  1.73692                                          51.15R44  -     145.50                   e44  1.125      AIRR45  +     79.43               )   e45  1.80  n45  1.81253                                          25.30R46  +     41.39               )   e46  12.60 n46  1.46619                                          65.56R47  -     157.83                   e47  5          AIRR48        ∞               )   e48  65.20 n48  1.51873                                          64.04R49        ∞   f1 = -34.77       h2 = -90.66   f2 =  73.49       h3 = 176.00    The variable distances e20 and h1 are given hereinafter for five different settings. Also shown are the magnifications g1, g2 and G corresponding to each adjustment, respectively. 
    
     
         ______________________________________e20     h1        g1        g2      G______________________________________235.03  3.66      0.200     0.312   0.0625128.56  20.35     0.414     0.539   0.22375.35   38.61     0.708     0.788   0.55845.42   54.20     1         1       11.08    84.79     1.654     1.416   2.343______________________________________ 
    
     FIGS. 5A to 5C of the drawings illustrate a fifth form of embodiment of the device of this invention, with the following composition: 
     Front movable component I: a convergent meniscus R16-R17, a divergent meniscus R18-R19, a doublet R20-R22 consisting of a divergent biconcave lens R20-R21 and of a convergent lens R21-R22. 
     Back movable component II: a doublet comprising a biconvex lens R23-R24, a divergent biconcave lens R24-R25, a biconvex lens R26-R27; a biconvex lens R28-R29 and a biconvex lens R30-R31. 
     Back fixed component IV: a doublet comprising a divergent biconcave lens R32-R33 and a biconvex lens R33-R34, a divergent biconcave lens R35-R36, a convergent meniscus R37-R38 having its concave surface directed towards the object, then another set of lenses comprising: two convergent meniscus R39-R40 and R41-R42 having their concave surfaces directed towards the object, a doublet comprising a biconvex lens R43-R44 and a divergent meniscus R44-R45, then a doublet consisting of a divergent meniscus R46-R47 of which the convex surface is directed towards the object, and of a biconvex lens R47-R48. 
     Front fixed component III: the first six elements R1 to R11 are similar to the elements R1 to R11 of the objective of FIGS. 4A to 4C. Then, this component comprises in succession: a convergent meniscus R12-R13, a biconvex lens R14-R15. 
     For better results with this form of embodiment, the following requirements should be met, f1 designating the focal length, bearing the sign-, of the front component: ##EQU9## 
     It is also advantageous to adhere to the following conditions: ##EQU10## 
     The following Table No. 5 corresponds to the embodiment of FIGS. 5A to 5C and provides a concrete example of a device meeting the requirements and conditions set forth hereinabove. In this Table, the same data designated by the same reference symbols as in the case of the preceding Tables are found. 
     
                       TABLE NO 5______________________________________R                    E       n     ne    e______________________________________R1   +     650.20               )   e1   3.50  n1    1.69402                                          54.53R2   +     132.53       e2   0.50        airR3   +     129.80               )   e3   12.40 n3    1.81253                                          25.30R4   +     234.44R5   -     225.33       e4   22          air               )   e5   3.20  n5    1.69402                                          54.53R6   +     8196.72R7   -     682.52       e6   8.50        air               )   e7   2.70  n7    1.81253                                          25.30R8   +     185.01               )   e8   22.   n8    1.48890                                          70.37R9   -     202.43       e9   0.20        airR10  +     328.30               )   e10  11.50 n10   1.64304                                          59.85R11  -     384.32       e11  0.10        airR12  -     2087.68               )   e12  4     n12   1.64304                                          59.85R13  -     593.82       e13  0.10        airR14  +     179.73               )   e14  11.   n14   1.64304                                          59.85R15  -     2173.91      e15  1.757       to    160.95R16  +     96               )   e16  1.90  n16   1.74794                                          44.55R17  +     36.39        e17  9.30        airR18  +     441.65               )   e18  1.90  n18   1.74794                                          44.55R19  +     76.47        e19  8.40        airR20  -     77.73               )   e20  1.90  n20   1.69402                                          54.53R21  +     44.44               )   e21  9.30  n21   1.81253                                          25.30R22  -     607.90       e22  248.718     to    0.93R23  +     1283.70               )   e23  7     n23   1.64304                                          59.85R24  -     153.66               )   e24  2.40  n24   1.81253                                          25.30R25  +     156.18       e25  0.50        airR26  +     158.73               )   e26  13.50 n26   1.64304                                          59.85R27  -     122.67       e27  0.10        airR28  +     215.56               )   e28  7.30  n28   1.62286                                          60.11R29  -     453.10       e29  0.10        airR30  +     153               )   e30  7.50  n30   1.62286                                          60.11R31  -     781.86       e31  13.10       to    101.69R32  -     127.99               )   e32  2.40  n32   1.69233                                          49.35R33  +     47.93               )   e33  14.40 n33   1.81253                                          25.30R34  -     270.56       e34  6           airR35  -     126.31               )   e35  2.40  n35   1.70448                                          29.88R36  +     123.50       e36  8.50        airR37  -     90.68               )   e37  3.80  n37   1.70586                                          40.82R38  -     67.23        e38  48          airR39  -     57.79               )   e39  6     n39   1.46619                                          65.56R40  -     56.39        e40  0.10        airR41  -     109.77               )   e41  6     n41   1.46619                                          65.56R42  -     62.27        e42  0.10        airR43  +     963.39               )   e43  8     n43   1.46619                                          65.56R44  -     41.37               )   e44  2     n44   1.73692                                          51.15R45  -     96.63        e45  3.30        airR46  +     94.52               )   e46  2     n46   1.81253                                          25.30R47  +     31.75               )   e47  8     n47   1.46619                                          65.56R48  -     144.91       e48  10          airR49        ∞               )   e49  65.20 n49   1.51873                                          64.04R50        ∞ f1 = -36.07        h2 = -98.91f2 = 79.18          h3 = 194.81______________________________________ 
    
     The variable distances e22 and h1 are given hereinafter for five different settings. Also shown are the magnifications g1, g2 and G corresponding to each adjustment, respectively. 
     
         ______________________________________e22     h1        g1        g2      G______________________________________248.72  3.00      0.200     0.319   0.0637137.00  21.13     0.416     0.548   0.22880.24   41.20     0.720     0.801   0.57750.49   56.96     1         1       10.93    91.59     1.706     1.437   2.453______________________________________ 
    
     Although the invention has been described with reference to specific and preferred forms of embodiment, it will readily appear to those conversant with the art that many constructional details may be modified without departing from the basic principles of the invention as disclosed in the appended claims. 
     As already mentioned hereinabove, the device constituting the subject-matter of the present invention is intended for producing the desired variable magnification or enlargement of an image from a fixed convergent optical element disposed in front thereof, another fixed element disposed at the back receiving the magnified image for giving the final image having the desired dimensions. Besides, this invention also includes an assembly thus formed which constitutes a variable focal length objective.