Abstract:
An objective lens comprises a housing, an iris diaphragm and a plurality of lens groups. For focusing the objective lens while minimizing the variation of the image angle at least two lens groups are adapted to be moved relative to the housing. The one lens group is arranged in front of the iris diaphragm. The other lens group is arranged at least partially behind the iris diaphragm.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of International Patent Application PCT/EP2005/009484, filed on Sep. 3, 2005 and published in German language, which international patent application claims priority from German Patent Application No. 10 2004 043 611.8, filed Sep. 7, 2004; German Patent Application No. 20 2004 020 515.7, filed Sep. 7, 2004 and German Patent Application No. 10 2005 025 204.4, filed May 25, 2005. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention is related to the field of objective lenses.  
         [0003]     More specifically, the invention is related to objective lenses in which no variation of the image angle occurs during focusing.  
         [0004]     Still more specifically, the invention is related to an objective lens having a housing, an iris diaphragm and a plurality of lens groups, wherein for focusing the objective lens while minimizing the variation of the image angle at least two lens groups are adapted to be moved relative to the housing, and one of the two lens groups is arranged in front of the iris diaphragm.  
       BACKGROUND OF THE INVENTION  
       [0005]     In zoom objective lenses having a plurality of lens groups, a separate front lens group is conventionally configured as a focus group and is moved during focusing. This separate focus group operates independently from those lens groups which vary the image scale during zooming. If no further measures are taken, the movement of the focus group during focusing of the image causes the image angle (also referred to as “image field angle”) to vary.  
         [0006]     In order to avoid this phenomenon, various measures have already been proposed, according to which the focus group is subdivided into two lens groups which are moved according to certain rules.  
         [0007]     Document DE 79 08 085 U1 mentioned at the outset discloses several such concepts in which these two lens groups are arranged in front of the iris diaphragm of the objective lens. According to a first variant, one lens group of the focus group is held stationary and only the other one is moved. According to a second variant, both lens groups are simultaneously moved during focusing, however, at different speeds. When doing so, the position of a rear main plane of the entire lens system remains unchanged.  
         [0008]     In an objective lens according to document U.S. Pat. No. 4,278,331 the two lens groups of the focus group being likewise positioned in front of the iris diaphragm, are moved in opposite directions relative to one another, such that the angle between a light beam directed onto the entrance pupil of the objective lens and the optical axis of the objective lens remains constant during focusing.  
         [0009]     Document U.S. Pat. No. 4,336,983 describes another objective lens having means for avoiding a variation of the image angle during focusing. In this objective lens only one lens group being arranged in front of the iris diaphragm is moved during focusing. Two further lens groups are not moved during focusing. An iris diaphragm is provided between the second and the third lens group. The focal point of the combination of the second and the third lens group coincides with the exit pupil of the entire lens system.  
         [0010]     The problem of avoiding variations of the image angle during focusing is also the subject of scientific publications, e.g. K. Tanaka “A Zoom Lens without Focus Breathing Phenomena”, Proc. of SPIE Vol. 4487 (2001), pages 63-67; I. Neil “High Performance Wide Angle Objective Lens Systems with Internal Close Focusing Optics and Multiple Aspheric Surfaces for the Visible Waveband”, SPIE, Vol. 2774, pages 216-242; I. Neil “High Performance, Wide Angle, Macro Focus, Zoom Lens for 35 mm Cinematography”, SPIE Vol. 3482, pages 213-228.  
         [0011]     The prior art objective lenses of the type specified before, have the disadvantage that due to the positioning of the moved focus group in front of the iris diaphragm negative influences occur with regard to the correction of the objective lens.  
       SUMMARY OF THE INVENTION  
       [0012]     It is an object underlying the invention to improve an objective lens of the type specified at the outset such that the afore-specified disadvantages are avoided. In particular, the objective lens shall not cause a variation of the image angle during focusing, i.e. the object-sided image angle shall remain constant at a given image height for all distances to an object, without having negative implications on the possibility to correct the objective lens.  
         [0013]     In an objective lens of the type specified at the outset, this object is achieved according to the invention in that the second lens group is arranged at least partially behind the iris diaphragm.  
         [0014]     The object underlying the invention is thus entirely solved. By placing a focusing group into the rear portion of the objective lens, it is achieved in a surprisingly simple manner that an objective lens is created that may be corrected easily and that has no variation of the image angle during focusing.  
         [0015]     Preferred embodiments of the invention are specified in claims  2  through  15 .  
         [0016]     It goes without saying that the features mentioned before and those that will be explained hereinafter may not only be used in the particularly given combination, but also in other combinations, or alone, without leaving the scope of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Embodiments of the invention are shown in the drawing and will be explained in further detail throughout the subsequent description.  
         [0018]      FIG. 1A  shows a first embodiment of an objective lens according to the invention having twelve lenses in four lens groups;  
         [0019]      FIG. 1B  shows a data sheet of the objective lens according to  FIG. 1A ;  
         [0020]      FIG. 2A  shows a second embodiment of an objective lens according to the invention having thirteen lenses in three lens groups;  
         [0021]      FIG. 2B  shows a data sheet of the objective lens according to  FIG. 2A ;  
         [0022]      FIG. 3A  shows a third embodiment of an objective lens according to the invention having twelve lenses in four lens groups;  
         [0023]      FIG. 3B  shows a data sheet of the objective lens according to  FIG. 3A ;  
         [0024]      FIG. 4A  shows a fourth embodiment of an objective lens according to the invention having twelve lenses in four lens groups;  
         [0025]      FIG. 4B  shows a data sheet of the objective lens according to  FIG. 4A . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     In  FIG. 1A  reference numeral  100  indicates a first embodiment of an objective lens according to the invention. Objective lens  100  has a housing  102  with an optical axis  104  and four lens groups I, II, III, and IV arranged along optical axis  104 . The front, i.e. object-sided end of objective lens  100  is designated  106  and the rear end is designated  108 . Objective lens  100  has an iris diaphragm  110  positioned within fourth lens group IV. Iris diaphragm  110  may be connected to fourth lens group IV or with housing  102 .  
         [0027]     Lens groups I, II, III, and IV comprise a total of twelve lenses  120  to  142 . From lenses  120  to  142 , lenses  120  to  124  belong to first lens group I, lenses  126  to  128  belong to second lens group II, lenses  130  to  132  belong to third lens group III, and lenses  134  to  142  belong to fourth lens group IV.  
         [0028]     The first two front lens groups I and II are preferably rigidly connected to housing  102 . The two other lens groups III and IV, however, are movably journalled within housing  102 . They may be moved independently from one another. For that purpose, two separate and differently configured guide grooves are, for example, provided at the periphery of a tube. Each one of these two grooves is a part of an individual drive train for one each of the two lens groups. Focusing is effected by a common actuator element. The elements required therefore are well-known to a person of ordinary skill, and, therefore, are not shown in  FIG. 1A .  
         [0029]     According to the conventional nomenclature the art of optical design, the surfaces and planes, respectively, are numbered in  FIG. 1A  as No.  1 ,  2 ,  3  . . . beginning at the left-hand side which holds also true for the other embodiments discussed further below and having different arrangements of lenses. For example, the sixth lens  130  has a left surface No.  12 . The sixth lens  130  and the neighbored seventh lens  132  have a common surface No.  13 .  
         [0030]     According to the invention lenses  130  and  132  of third lens group III and lenses  134  to  142  of fourth lens group IV configure the two focus groups which may be moved independently from one another for focusing. Insofar, it is important to notice that fourth lens group IV is arranged partially behind iris diaphragm  110 . One may also provide more than two focus groups.  
         [0031]     Lens No.  15 , preferably, is configured aspherical.  
         [0032]     A preferred embodiment according to  FIG. 1 , and in the nomenclature of the so-called “code V” has the following data which are also depicted in  FIG. 1B :  
                                                                                               Focal Length:   49.99 mm           Aperture Stop Area:   17           Front Focus Group (III):   Surfaces No. 12 to 14           Rear Focus Group (IV):   Surfaces No. 15 to 25                        Nr.   Radius   Distance   nd   nv               1   ∞   0.000       2   −290.07000   4.000   1.48751   70.40       3   50.11900   16.200       4   −122.32000   7.500   1.75528   27.58       5   −70.79500   11.700       6   −52.70800   4.100   1.65416   39.63       7   −658.79000   1.300       8   434.01000   18.000   1.52875   76.97       9   −60.43000   0.300       10   78.86300   15.400   1.49702   81.54       11   −196.68000   10.361       12   46.63900   16.700   1.72005   43.69       13   −143.30000   4.000   1.65416   39.63       14   103.66000   1.000       15   92.48961   4.000   1.71743   29.62       16   31.62300   9.320       17   ∞   7.000       18   −31.85100   4.000   1.67276   32.21       19   114.65000   3.560       20   −170.31000   7.300   1.74104   52.64       21   −47.31500   0.200       22   202.42000   7.500   1.52857   76.97       23   −74.45200   0.200       24   69.78300   10.400   1.49702   81.54       25   −82.93700   36.004       26   ∞   0.000                        Aspherical surface:   S15               Series constants:   A:   −1.132e−006                B:   4.950e−010               C:   −1.325e−013                D:   6.213e−016                      
 
         [0033]     wherein the quantities nd and vd are material designations for the particularly used class, namely nd is the index of refraction for a helium-d line of 587.56 nm and vd is the so-called Abbe number. The series constants A to D are the series constants known to the person of ordinary skill for aspherical optical surfaces (series expansion of the cone section).  
         [0034]     In  FIG. 2A , reference numeral  200  designates a second embodiment of an objective lens according to the invention. Objective lens  200  has a housing  202 , an optical axis  204  and three lens groups I, II, and III arranged along the latter. The front, i.e. object sided end of objective lens  200 , is designated  206  and the rear end is designated  208 . Objective lens  200  has an iris diaphragm  210  positioned within third lens group III. Iris diaphragm  210  may be connected to third lens group III or to housing  202 .  
         [0035]     Lens groups I, II, and III comprise a total of thirteen lenses  220  through  244 . Lenses  220  and  222  belong to first lens group I, lenses  224  and  226  belong to second lens group II, and lenses  228  to  244  belong to third lens group III.  
         [0036]     The first, front lens group I, preferably, is rigidly connected to housing  202 . The two other lens groups II and III, however, are movable journalled within housing  202 . They may be moved independently from one another.  
         [0037]     Fifth lens  228  and neighbored sixth lens  230  configure a common surface No.  12 . This applies, mutatis mutandis, for eighth lens  234  and ninth lens  236 , as well as for twelfth lens  242  and thirteenth lens  244  with common surfaces No.  18  and No.  25 , respectively.  
         [0038]     According to the invention, lenses  224  and  226  of second lens group II and lenses  228  to  244  of third lens group III configure the two focus groups which are movable independently from one another for focusing. Insofar, it is important to note that third lens group III is partially positioned behind iris diaphragm  210 .  
         [0039]     Surface No.  23 , preferably, is configured aspherical.  
         [0040]     A preferred embodiment according to  FIG. 2A  has the following data which are also shown in  FIG. 2B :  
                                                                                               Focal Length:   65.00 mm           Aperture Stop Area:   16           Front Focus Group (II):   Surfaces No. 7 to 10           Rear Focus Group (III):   Surfaces No. 11 to 26                        Nr.   Radius   Distance   nd   nv               1   ∞   2.551       2   554.31000   4.310   1.69901   30.13       3   82.93700   7.670       4   1539.90000   8.050   1.80527   25.42       5   −185.67000   4.670   1.81605   46.62       6   −188.36000   7.281       7   52.33000   16.110   1.61803   63.33       8   11548.00000   0.110       9   70.79500   4.200   1.71743   29.62       10   55.03300   2.534       11   42.47400   4.270   1.80527   25.42       12   35.48100   7.820   1.81605   46.62       13   46.63900   4.790       14   183.02000   4.200   1.55839   54.01       15   25.11900   9.800       16   ∞   9.710       17   −23.04100   4.200   1.65416   39.63       18   39.52500   16.230   1.61803   63.33       19   −44.66800   0.350       20   66.47300   10.020   1.60303   65.44       21   −240.57000   0.210       22   466.39000   7.510   1.60303   65.44       23   −88.45271   0.100       24   91.72800   4.200   1.81605   46.62       25   27.98200   16.460   1.61803   63.33       26   −128.64000   39.014       28   ∞   0.00                        Aspherical surface:   S23               Series constants:   A:   2.316e−006               B:   1.036e−009               C:   −7.878e−013                D:   1.079e−015                      
 
         [0041]     In  FIG. 3A , reference numeral  300  designates a third embodiment of an objective lens according to the invention. Objective lens  300  has a housing  302  with an optical axis  304  and four lens groups I, II, III, and IV arranged along the latter. The front, i.e. the object-sided end of objective lens  300 , is designated  306  and the rear end is designated  308 . Objective lens  300  has an iris diaphragm  310  arranged in front of fourth lens group IV. Iris diaphragm  310  may be connected to fourth lens group IV or to housing  302 .  
         [0042]     Lens groups I, II, III, and IV comprise a total of twelve lenses  320  to  342 . Lenses  320  to  324  belong to first lens group I, lenses  326  and  328  belong to second lens group II, lenses  330  and  332  belong to third lens group III, and lenses  334  to  342  belong to fourth lens group IV.  
         [0043]     The first and the second front lens groups I and II are, preferably, rigidly connected to housing  302 . The two other lens groups III and IV, however, are movably journalled within housing  302 . They may be moved independently from one another.  
         [0044]     Second lens  322  and neighbored third lens  324  configure a common surface No.  5 . This holds also true, mutatis mutandis, for sixth lens  330  and seventh lens  332 , as well as for ninth lens  336  and tenth lens  338  having common surfaces No.  12  and No.  18 , respectively.  
         [0045]     According to the invention, lenses  330  and  332  of third lens group III and lenses  334  to  342  of fourth lens group IV configure the two focus groups which may be moved independently from one another for focusing. Insofar, it is important to note that fourth lens group IV is positioned behind iris diaphragm  310 .  
         [0046]     Surface No.  15 , preferably, is configured aspherical.  
         [0047]     A preferred embodiment according to  FIG. 3  has the following data and is also shown in  FIG. 3B :  
                                                                                               Focal Length:   74.98 mm           Aperture Stop Area:   14           Front Focus Group (III):   Surfaces No. 11 to 13           Rear Focus Group (IV):   Surfaces No. 14 to 23                        Nr.   Radius   Distance   nd   nv               1   ∞   0.000       2   −755.31000   7.800   1.51635   64.14       3   74.45200   11.000       4   −446.68000   4.500   1.51682   64.17       5   68.78600   15.100   1.62017   63.48       6   −403.88000   5.760       7   103.66000   14.000   1.43876   94.99       8   −233.75000   5.410       9   67.80300   12.900   1.49702   81.54       10   453.16000   16.753       11   70.79500   11.850   1.71705   47.93       12   −202.42000   11.500   1.65416   39.63       13   81.75200   6.413       14   ∞   2.670       15   −260.53296   3.600   1.71743   29.51       16   37.04700   8.900       17   −35.22700   3.600   1.61664   36.63       18   52.70800   10.200   1.78805   47.37       19   −53.08800   0.200       20   −202.4200   5.700   1.81605   46.62       21   −63.09600   0.200       22   50.11900   7.000   1.49702   81.54       23   1295.70000   36.153       24   ∞   0.000                        Aspherical surface:   S15               Series constants:   A:   3.750e−006               B:   3.704e−010               C:   −5.545e−013                D:   0.000e+000                      
 
         [0048]     In  FIG. 4A , reference numeral  400  designates a fourth embodiment of an objective lens according to the invention. Objective lens  400  has a housing  402  with an optical axis  404 , and four lens groups I, II, III, and IV arranged along the latter. The front, i.e. the object-sided end of objective lens  400 , is designated  406 , and the rear end is designated  408 . Objective lens  400  has an iris diaphragm  410  which is positioned in front of fourth lens group IV. Iris diaphragm  410  may be connected to fourth lens group IV or to housing  402 .  
         [0049]     Lens groups I, II, III, and IV comprise a total of twelve lenses  420  to  442 . Lenses  420  and  422  belong to first lens group I, lenses  424  and  426  belong to second lens group II, lenses  428  and  430  belong to third lens group III, and lenses  432  to  442  belong to fourth lens group IV.  
         [0050]     The first and the second, front lens groups I and II are, preferably, rigidly connected to housing  402 . The two other lens groups III and IV, however, are movably journalled within housing  402 . They may be moved independently from one another.  
         [0051]     Seventh lens  432  and neighbored eighth lens  434  configure a common surface No.  16 . This holds also true, mutatis mutandis, for tenth lens  438  and eleventh lens  440  having a common surface No.  21 .  
         [0052]     According to the invention, lenses  428  and  430  of third lens group III and lenses  432  to  442  of fourth lens group IV configure the two focus groups which may be moved independently from one another for focusing. Insofar, it is important to note that fourth lens group IV is positioned behind iris diaphragm  410 .  
         [0053]     Surface No.  12 , preferably, is configured aspherical.  
         [0054]     A preferred embodiment according to  FIG. 4A  has the following data which are also shown in  FIG. 4B :  
                                                                                               Focal Length:   99.80 mm           Aperture Stop Area:   14           Front Focus Group (III):   Surfaces No. 10 to 13           Rear Focus Group (IV):   Surfaces No. 14 to 22                        Nr.   Radius   Distance   nd   Nv               1   ∞   0.000       2   −1883.60000   4.700   1.54075   47.23       3   101.45000   3.140       4   127.72000   15.680   1.61803   63.33       5   −281.84000   0.200       6   66.35500   14.780   1.43876   94.99       7   202.42000   0.100       8   113.83000   4.850   1.80527   25.42       9   89.12500   14.959       10   52.33000   14.190   1.75704   47.82       11   381.29000   7.540       12   −230.02127   2.800   1.61344   44.29       13   29.64000   16.343       14   ∞   18.938       15   −27.58200   2.970   1.61344   44.29       16   285.92000   12.520   1.69104   54.82       17   −41.86700   0.550       18   188.36000   8.180   1.69104   54.82       19   −76.07600   0.100       20   110.60000   10.690   1.60303   65.44       21   −46.30500   2.800   1.65416   39.63       22   153.99000   1.000       23   73.91800   4.220   1.49702   81.54       24   158.49000   40.123       25   ∞   0.0                        Aspherical surface:   S12               Series constants:   A:   8.669e−007               B:   9.230e−011               C:   2.783e−014               D:   −9.209e−016                E:   1.576e−018               F:   −8.587e−022                       
 
         [0055]     For all embodiments described above, the following equation: 
 
 f ′( e )= f ′(∞)/(1 −f ′( e )*β( e )/ APF ) 
 
         [0056]     preferably applies with a maximum deviation of less than 10% wherein f′(e) is the focal length of the objective lens when a distance e to an object is set, f′(∞) is the focal length of the objective lens when a distance ∞ to an object is set, β(e) is the imaging scale of the objective lens when a distance ∞ to an object is set, and APF is the distance between the exit pupil and the focal point. For the various lens groups in the four described embodiments, this results in the following values:  
       EXAMPLE 1  
     FIGS.  1 A und  1 B  
       [0057]    
       
         
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
               
                   
                 Lens 
                   
                   
                 f′(∞)/(1 − f′(e) * 
                   
               
               
                   
                 Group 
                 β(e) 
                 f′(e) 
                 β(e)/APF) 
                 Δ/% 
               
               
                   
                   
               
             
             
               
                   
                 I 
                 0.000 
                 49.989 
                 49.989 
                 0.000 
               
               
                   
                 II 
                 0.027 
                 49.615 
                 49.366 
                 0.503 
               
               
                   
                 III 
                 0.059 
                 49.147 
                 48.671 
                 0.978 
               
               
                   
                 IV 
                 0.142 
                 47.834 
                 47.010 
                 1.753 
               
               
                   
                   
               
             
          
         
       
     
       EXAMPLE 2  
     FIGS.  2 A und  2 B  
       [0058]    
       
         
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
               
                   
                 Lens 
                   
                   
                 f′(∞)/(1 − f′(e) * 
                   
               
               
                   
                 Group 
                 β(e) 
                 f′(e) 
                 β(e)/APF) 
                 Δ/% 
               
               
                   
                   
               
             
             
               
                   
                 I 
                 0.000 
                 65.000 
                 65.000 
                 0.000 
               
               
                   
                 II 
                 0.074 
                 64.523 
                 64.169 
                 0.551 
               
               
                   
                 III 
                 0.125 
                 64.216 
                 63.612 
                 0.950 
               
               
                   
                   
               
             
          
         
       
     
       EXAMPLE 3  
     FIGS.  3 A und  3 B  
       [0059]    
       
         
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
               
                   
                 Lens 
                   
                   
                 f′(∞)/(1 − f′(e) * 
                   
               
               
                   
                 Group 
                 β(e) 
                 f′(e) 
                 β(e)/APF) 
                 Δ/% 
               
               
                   
                   
               
             
             
               
                   
                 I 
                 0.000 
                 74.985 
                 74.985 
                 0.000 
               
               
                   
                 II 
                 0.015 
                 74.599 
                 74.237 
                 0.488 
               
               
                   
                 III 
                 0.040 
                 73.940 
                 73.086 
                 1.169 
               
               
                   
                 IV 
                 0.112 
                 71.926 
                 70.051 
                 2.677 
               
               
                   
                   
               
             
          
         
       
     
       EXAMPLE 4  
     FIGS.  4 A und  4 B  
       [0060]    
       
         
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
               
                   
                 Lens 
                   
                   
                 f′(∞)/(1 − f′(e) * 
                   
               
               
                   
                 Group 
                 β(e) 
                 f′(e) 
                 β(e)/APF) 
                 Δ/% 
               
               
                   
                   
               
             
             
               
                   
                 I 
                 0.000 
                 99.797 
                 99.797 
                 0.000 
               
               
                   
                 II 
                 0.019 
                 98.880 
                 98.652 
                 0.231 
               
               
                   
                 III 
                 0.062 
                 97.122 
                 96.209 
                 0.950 
               
               
                   
                 IV 
                 0.114 
                 95.399 
                 93.311 
                 2.238