Abstract:
The invention is directed to an objective, particularly for telescope-type stereomicroscopes. The objective comprises two lens groups, a first lens group and a second lens group. The first lens group, which faces the object plane, has a positive refractive power and comprises a plurality of lenses of which at least two form a cemented component. The second lens group, which is on the image side, has a negative refractive power and comprises a collecting cemented component and a diverging lens. The objective is characterized in that the following conditions B 1  and B 2  are met: 
     where D AP  represents the diameter of the exit pupil of the objective and ω 1  represents the maximum field angle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of International Application No. PCT/EP2005/010473, filed Sep. 28, 2005, German Application No. 10 2004 048 299.3, filed Oct. 1, 2004 and German Application No. 10 2005 046 476.9, filed Sep. 26, 2005, the complete disclosures of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   a) Field of the Invention 
   The invention is directed to a microscope objective, particularly for stereomicroscopes, which has a large pupil diameter and is used with incident brightfield illumination. 
   b) Description of the Related Art 
   In telescope-type stereomicroscopes, two separate light channels are guided through one and the same objective in order to achieve a stereoscopic impression. As a result, the dimensions of an objective of this kind, especially with regard to the lens diameter, are significantly larger than those of objectives for conventional microscopes or in Greenough-type stereomicroscopes. In addition, requirements for microscope objectives with regard to the correction of the chromatic aberration, field flattening and prevention of distortion are increasingly demanding. 
   The objectives are usually used in connection with a focal magnification changers and exchangeable tubes. In order to make it possible to use the microscope at magnifications which allow overview imaging of an object as well as detailed viewing without having to change objectives, objectives are required in which there is more space available for suitable magnification changers in the post-magnification area and which also offer a larger usable aperture in the object space. 
   The use of fluorescence in stereomicroscopes with incident brightfield illumination places new demands on the design of the objectives. Accordingly, with regard to the devices, it is necessary to separate the beam paths of the excitation of the fluorescence and of the observation in the entrance aperture from the device in the objective. This leads to large apertures. Requirements regarding correction are demanding in objectives of this kind for telescope-type stereomicroscopes. In addition, because of the fluorescence excitation the selection of material is limited with respect to transparency and self-fluorescence of the materials which are employed. 
   EP 1 369 729 A2 describes an objective for telescope-type stereomicroscopes which comprises three optical lens groups. The first lens group is arranged toward the object side and the third lens group is arranged toward a magnification changer. This objective satisfies certain conditions with resect to the diameter of the entrance pupil of the magnification changer arranged downstream of the objective and of the maximum field angle of the objective at low magnification. 
   JP 2001-147378 describes an objective which is suitable for use in telescope-type stereomicroscopes. Viewed from the direction of the microscope body, they comprise a first lens group with positive refractive power, a second lens group containing at least one cemented triplet, and a third lens group with positive refractive power. These lens groups can also comprise individual lenses in addition to the cemented components or combinations of individual lenses and cemented components. 
   JP 2001-221955 describes another objective for telescope-type stereomicroscopes. Viewed from the direction of the microscope body, the objective comprises two lens groups of which a first lens group with positive refractive power contains a biconvex cemented component and a second lens group contains at least two cemented components. In addition to the cemented components, the lens groups can also comprise individual lenses as well as combinations of individual lenses and cemented components. 
   U.S. Pat. No. 6,271,971 describes an objective for telescope-type stereomicroscopes with the primary aim of optimizing the ratio of mounting space to the objective focal length. 
   OBJECT AND SUMMARY OF THE INVENTION 
   Accordingly, it is the primary object of the invention to provide an objective for telescope-type stereomicroscopes in a simple compact construction which satisfies requirements regarding the correction of the chromatic aberration and distortion while meeting the demands for more space for magnification changers and for a larger useful aperture in the object space and which realizes a large working distance and a flat visual field. 
   This object is met in an objective with two lens groups comprising individual lenses and, in each instance, at least one cemented component, where the conditions
 
46.5&lt;D AP ≦60 and  B 1  
 
0.16≦tan ω 1   B 2  
 
are met, D AP  represents the exit diameter of the objective and ω 1  represents the angle of the maximum field.
 
   The lens groups can comprise individual lenses, at least one cemented component, or a combination of individual lenses and cemented components. 
   An advantageous objective has a focal length f′≧40 mm and ≦200 mm. 
   It is advantageous when the illumination beam path is coupled into the exit pupil of the objective. 
   In particular, it is advantageous when the center points of the entrance pupil of the illumination beam path and the center points of the two beam paths of the objective form an isosceles triangle inside the exit pupil of the objective, the center point of the exit pupil lying inside this triangle. 
   With respect to the exit pupil of the objective, it is advantageous when the following conditions are met:
 
0.25≦ a   1   /D   AP ≦0.5
 
0.25≦ a   2   /D   AP ≦0.5
 
0.25≦ a   3   /D   AP ≦0.5,
 
where a 1  and a 2  are the distances of the center points M 1  and M 2  of the two beam paths of the objective from the center point M of the exit pupil of the objective, and a 3  is the distance of the center point M 3  of the entrance pupil of the illumination beam path from the center point M of the exit pupil of the objective.
 
   Accordingly, it is also advantageous when the focal length of this second lens group satisfies the following condition:
 
−0.0668* f′   2 +7.4933* f′− 460≦ f′   2 ≦−0.0668 f′   2 +7.4933* f′− 400,
 
where f′ 2  is the focal length of the second lens group and f′ is the total focal length of the objective.
 
   An advantageous objective is also provided when the second lens group comprises a cemented component and an individual lens, and the cemented component is arranged next to the magnification changer and when the focal length of this second lens group satisfies the following condition:
 
−0.0668* f′   2 +7.4933* f′− 460≦ f′   2 ≦−0.0668 f′   2 +7.4933* f′− 400,
 
where f′ 2  is the focal length of the second lens group and f′ is the total focal length of the objective. The individual lens is preferably constructed as a meniscus with the convex side facing the object.
 
   It is also advantageous when the cemented component of the second lens group meets the condition:
 
10 −8   *f′   2 +9*10 −8   *f′− 10 −4 ≦1/ f   1 /ν e1 +1/ f   2 /ν e2 ≦10 −8   *f′   2 +9*10 −8   *f′− 10 −4 ,
 
and lens  2 . 1  of this lens group meets the condition ν e3 ≦55, where f′ 1  is the focal length of lenses  2 . 22 , f′ 2  is the focal length of lenses  2 . 21 , f′ is the total focal length of the objective, ν e1  and ν e2  are the Abbe numbers of lenses  2 . 22  and  2 . 21 , and ν e3  is the Abbe number of lens  2 . 1 .
 
   In the inventive construction, the first lens group has a positive refractive power and comprises a plurality of lenses of which at least two form a cemented component. The second lens group has a negative refractive power and comprises a collecting cemented component and a diverging lens. 
   An advantageous first construction of the objective with a focal length f′=50 mm, an entrance aperture of 55 mm and an aperture ratio of 1:0.9 is realized by the constructional data indicated in claim  10 . This first construction comprises two lens groups, wherein considered from the object space, a first lens group with positive refractive power comprises two individual lenses with positive refractive power and a cemented group comprising two lenses, followed by an individual lens with positive refractive power and a second lens group with negative refractive power comprising another individual lens with negative refractive power and a cemented group with positive refractive power comprising two lenses. 
   An advantageous second construction of the objective with a focal length f′=100 mm, an entrance aperture of 55 mm and an aperture ratio of 1:1.8 is realized by the constructional data indicated in claim  11 . This second construction likewise comprises two lens groups, wherein, considered from the object space, a first lens group with positive refractive power comprises a cemented group comprising two lenses and an individual lens with positive refractive power and a second lens group with negative refractive power comprising an individual lens with negative refractive power and a cemented group with positive refractive power comprising two lenses. 
   A third construction of the objective with a focal length f′=80 mm, an entrance aperture of 55 mm and an aperture ratio of 1:1.45 can be produced by the constructional data indicated in claim  12 . This third construction likewise comprises two lens groups, wherein, considered from the object space, a first lens group with positive refractive power comprises two individual lenses with positive refractive power, a cemented group comprising two lenses and another individual lens with positive refractive power, and a second lens group with negative refractive power comprising an individual lens with negative refractive power and a cemented group with positive refractive power comprising two lenses. 
   An advantageous fourth construction of the objective with a focal length f′=65.59 mm, an entrance aperture of 53.5 mm and an aperture ratio of 1:1.23 can be produced by the constructional data indicated in claim  13 . This fourth construction likewise comprises two lens groups, wherein, considered from the object space, a first lens group with positive refractive power comprises two individual lenses with positive refractive power, a cemented group comprising two lenses, and another individual lens with positive refractive power, and a second lens group with negative refractive power comprising an individual lens with negative refractive power and a cemented group with positive refractive power comprising two lenses. 
   An objective which is advantageously applicable in fluorescence stereomicroscopes is achieved when the condition τ(350; 5) j ≧0.8 is met, where τ(350; 5) j  is the medium-internal transmission at a wavelength of the light of 350 nm and a substrate thickness of 5 mm, and an index j=1, 2, . . . stands for all optical media of the objective. 
   The microscope objective that is provided in this way is particularly suited for use in fluorescence stereomicroscopy with incident brightfield illumination and, above all, offers advantages in this regard over known objectives. Further, there are advantages with respect to the correction of the chromatic aberration, field flattening and distortion as well as with respect to the demand for larger spaces for the magnification changers arranged downstream of the objective and for a larger useful aperture in the object space. 
   The invention will be described more fully in the following with reference to embodiment examples shown in the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  shows the construction of a telescope-type stereomicroscope in a highly simplified manner; 
       FIG. 2  shows a first embodiment example of an objective; 
       FIG. 3  shows a second embodiment example of an objective; 
       FIG. 4  shows a third embodiment example of an objective; and 
       FIG. 5  shows the arrangement of the different pupils in the objective pupil; and 
       FIG. 6  shows a fourth embodiment example of an objective. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The construction of a telescope-type stereomicroscope is shown as a block diagram in  FIG. 1  for purposes of illustration. The stereomicroscope comprises an objective  1  which, according to the invention, comprises a first lens group LG 1  and a second lens group LG 2  considered from the object  3  being observed which is arranged in an object plane  2 . Toward the image side, a magnification changer  8  and  9  and tube lenses  10  and  11 , in that sequence, are arranged downstream of the objective  1  in two separate beam paths  6  and  7 . The object  3  is imaged in the image plane  12  of the respective beam path  7  and  8  as a real intermediate image  13  and  14 . An eyepiece  15  and  16  is provided for observing the intermediate images  13  and  14  in each beam path  6 ,  7 . 
   As is conventional in stereomicroscopes of the type mentioned above, the two tube systems take two parallel partial bundles from the parallel beam bundles offered by the objective  1 . In so doing, an off-axis object point is introduced through the objective into downstream optics, e.g., a magnification changer, into their entrance pupil at an angle ω. 
   In the embodiment example shown in  FIG. 2 , the objective comprises, considered from the object plane in direction of the image plane  12 , a first lens group LG 1  followed by a second lens group LG 2 . Lens group LG 1  in its entirety has a positive refractive power and lens group LG 2  in its entirety has a negative refractive power. 
   As can further be seen from  FIG. 2 , the first lens group LG 1  comprises five lenses  1 . 1  to  1 . 5  of which lenses  1 . 3  and  1 . 4  are cemented together to form a cemented component. Lens group LG 2  comprises a lens  2 . 1  with negative refractive power and a cemented component  2 . 2  with positive refractive power. The cemented group  2 . 2  comprises another lens  2 . 21  and a lens  2 . 22  with positive refractive power. This microscope objective has the following constructional data showing radii r in mm, distances d in mm, refractive indices n e , and Abbe numbers ν e : 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
             
             
                 
               Radius 
               Distance d 
                 
                 
             
             
               Lens 
               mm 
               mm 
               n e   
               ν e   
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                 
               object plane 
                 
                 
             
             
                 
                 
               33.23399 
             
             
                 
               −143.28340 
             
             
               1.1 
                 
               12.70000 
               1.498450 
               81.30 
             
             
                 
               −45.64480 
             
             
                 
                 
               0.20000 
             
             
                 
               −156.22550 
             
             
               1.2 
                 
               10.00000 
               1.498450 
               81.30 
             
             
                 
               −61.77000 
             
             
                 
                 
               0.20000 
             
             
                 
               487.02500 
             
             
               1.3 
                 
               9.00000 
               1.747940 
               44.60 
             
             
                 
               86.59320 
             
             
               1.4 
                 
               21.20000 
               1.498450 
               81.30 
             
             
                 
               −86.59320 
             
             
                 
                 
               0.20000 
             
             
                 
               65.55050 
             
             
               1.5 
                 
               22.70000 
               1.498450 
               81.30 
             
             
                 
               334.94300 
             
             
                 
                 
               6.71704 
             
             
                 
               172.77720 
             
             
               2.1 
                 
               9.40000 
               1.584820 
               40.56 
             
             
                 
               48.69730 
             
             
                 
                 
               7.59559 
             
             
                 
               193.86600 
             
             
               2.21 
                 
               6.00000 
               1.607180 
               37.76 
             
             
                 
               79.72170 
             
             
               2.22 
                 
               8.80000 
               1.498450 
               81.30 
             
             
                 
               −258.51300 
             
             
                 
             
           
        
       
     
   
   This objective  1  has a focal length of 50 mm, an entrance aperture of 55 mm, and an aperture ratio of 1:0.9. 
     FIG. 3  shows an example for a second construction of an objective according to the invention. This objective likewise has two lens groups LG 1  and LG 2 . The first, object-side, lens group LG 1  has three lenses  1 . 1  to  1 . 3  of which lenses  1 . 1  and  1 . 2  are cemented together. Lens group LG 2  comprises a lens  2 . 1  with negative refractive power and a cemented component  2 . 2  with positive refractive power which comprises lenses  2 . 21  and  2 . 22 . 
   This microscope objective has the following constructional data showing radii r in mm, distances d in mm, refractive indices n e  and Abbe numbers ν e : 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
             
             
                 
               Radius 
               Distance d 
                 
                 
             
             
               Lens 
               mm 
               mm 
               n e   
               ν e   
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                 
               object plane 
                 
                 
             
             
                 
                 
               81.08262 
             
             
                 
               109.02830 
             
             
               1.1 
                 
               27.00000 
               1.498450 
               81.05 
             
             
                 
               −45.97500 
             
             
               1.2 
                 
               9.70000 
               1.758440 
               52.09 
             
             
                 
               −133.35410 
             
             
                 
                 
               0.15000 
             
             
                 
               101.08200 
             
             
               1.3 
                 
               14.70000 
               1.498450 
               81.05 
             
             
                 
               −128.62950 
             
             
                 
                 
               1.91858 
             
             
                 
               120.58530 
             
             
               2.1 
                 
               8.70000 
               1.616640 
               44.27 
             
             
                 
               45.64480 
             
             
                 
                 
               11.20295 
             
             
                 
               152.25440 
             
             
               2.21 
                 
               7.80000 
               1.518720 
               63.96 
             
             
                 
               41.86920 
             
             
               2.22 
                 
               14.00000 
               1.622470 
               63.19 
             
             
                 
               613.12200 
             
             
                 
             
           
        
       
     
   
   This objective  1  has a focal length of 100 mm, an entrance aperture of 55 mm, and an aperture ratio of 1:1.8. 
     FIG. 4  shows another objective according to the invention. This third construction of the objective with a focal length f′=80 mm, an entrance aperture of 55 mm and an aperture ratio of 1:1.45 likewise comprises two lens groups LG 1  and LG 2 , wherein, considered from the object space, the first lens group LG 1  with positive refractive power comprises two individual lenses  1 . 1  and  1 . 2 , each with positive refractive power, a cemented group comprising two lenses  1 . 2  and  1 . 4 , and another lens  1 . 5  with positive refractive power, and a second lens group LG 2  with negative refractive power comprising a lens  2 . 1  with negative refractive power and a cemented group  2 . 2  comprising two lenses  2 . 21  and  2 . 22 . 
   This microscope objective which is shown in  FIG. 4  has the following constructional data showing radii r in mm, distances d in mm, refractive indices n e  and Abbe numbers ν e : 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
             
             
                 
               Radius 
               Distance d 
                 
                 
             
             
               Lens 
               mm 
               mm 
               n e   
               ν e   
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                 
               object plane 
                 
                 
             
             
                 
                 
               61.00000 
             
             
                 
               330.28404 
             
             
               1.1 
                 
               11.10000 
               1.530190 
               67.58 
             
             
                 
               −87.89693 
             
             
                 
                 
               0.15000 
             
             
                 
               179.10180 
             
             
               1.2 
                 
               13.50000 
               1.530190 
               67.58 
             
             
                 
               −81.26925 
             
             
                 
                 
               2.04381 
             
             
                 
               −76.62790 
             
             
               1.3 
                 
               7.00000 
               1.758440 
               52.10 
             
             
                 
               56.32682 
             
             
               1.4 
                 
               18.70000 
               1.487940 
               80.07 
             
             
                 
               −160.14134 
             
             
                 
                 
               0.15000 
             
             
                 
               78.20610 
             
             
               1.5 
                 
               17.40000 
               1.530190 
               67.58 
             
             
                 
               −121.89972 
             
             
                 
                 
               0.15000 
             
             
                 
               82.85538 
             
             
               2.1 
                 
               7.0000 
               1.758440 
               52.10 
             
             
                 
               49.22050 
             
             
                 
                 
               10.76007 
             
             
                 
               214.01477 
             
             
               2.21 
                 
               7.0000 
               1.510450 
               60.98 
             
             
                 
               65.99372 
             
             
               2.22 
                 
               7.65175 
               1.622860 
               60.08 
             
             
                 
               276.92831 
             
             
                 
             
           
        
       
     
   
   This objective  1  has a focal length of 80 mm, an entrance aperture of 55 mm, and an aperture ratio of 1:1.45. 
     FIG. 5  shows the position of the different pupils in the exit pupil AP. These are the pupils having center points M 1  and M 2  of the two observation beam paths of the stereomicroscope and the entrance pupil M 3  of the illumination beam path which is coupled into the exit pupil AP of the objective  1 . These three pupils, whose center points are designated by M 1 , M 2  and M 3 , are arranged in the exit pupil AP in such a way that their center points M 1 , M 2  and M 3  form an isosceles triangle, and center point M of the exit pupil AP lies within this triangle, where the following conditions must be met:
 0.25≦ a   1   /D   AP ≦0.5 0.25≦ a   2   /D   AP ≦0.5. 0.25≦ a   3   /D   AP ≦0.5, 
where a 1  and a 2  are the distances of the center points M 1  and M 2  of the two beam paths of the objective  1  from the center point M of the exit pupil AP of the objective  1 , and a 3  is the distance of the center point M 3  of the entrance pupil of the illumination beam path from the center point M of the exit pupil AP of the objective  1 .
 
     FIG. 6  shows another objective according to the invention. This fourth construction of the objective with a focal length f′=65.59 mm, an entrance aperture of 53.5 mm and an aperture ratio of 1:1.23 likewise comprises two lens groups LG 1  and LG 2 , wherein, considered from the object space, the first lens group LG 1  with positive refractive power comprises an individual lens  1 . 1  with positive refractive power, a cemented group with negative refractive power comprising two lenses  1 . 2  and  1 . 3 , and another lens  1 . 4  with positive refractive power, and a second lens group LG 2  with negative refractive power comprising a lens  2 . 1  with negative refractive power and a cemented group  2 . 2  comprising two lenses  2 . 21  and  2 . 22 . 
   This microscope objective which is shown in  FIG. 6  has the following constructional data showing radii r in mm, distances d in mm, refractive indices n e  and Abbe numbers ν e : 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
             
             
                 
               Radius 
               Distance d 
                 
                 
             
             
               Lens 
               mm 
               mm 
               n e   
               ν e   
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                 
               object plane 
                 
                 
             
             
                 
                 
               49.60000 
             
             
                 
               −378.759 
             
             
               1.1 
                 
               15.00000 
               1.4980 
               81:1 
             
             
                 
               −46.980 
             
             
                 
                 
               0.21000 
             
             
                 
               135.296 
             
             
               1.2 
                 
               20.50000 
               1.440 
               94.6 
             
             
                 
               −46.308 
             
             
               1.3 
                 
               4.50000 
               1.716 
               53.6 
             
             
                 
               −415.764 
             
             
                 
                 
               0.20000 
             
             
                 
               71.814 
             
             
               1.4 
                 
               17.90000 
               1.440 
               94.6 
             
             
                 
               −254.821 
             
             
                 
                 
               1.77000 
             
             
                 
               89.771 
             
             
               2.1 
                 
               14.40000 
               1.489 
               70.2 
             
             
                 
               48.347 
             
             
                 
                 
               8.20000 
             
             
                 
               237.162 
             
             
               2.2 
                 
               4.50000 
               1.716 
               53.6 
             
             
                 
               68.294 
             
             
               2.3 
                 
               12.20000 
               1.498 
               81.1 
             
             
                 
               −125.885 
             
             
                 
                 
               0.40000 
             
             
                 
             
           
        
       
     
   
   This objective  1  has a focal length of 65.59 mm, an entrance aperture of 53.5 mm, and an aperture ratio of 1:1.23. 
   In this objective, the focal length of the second lens group satisfies the following condition:
 
−0.0668* f′   2 +7.4933* f′− 780≦ f′   2 ≦−0.0668 f′   2 +7.4933* f′− 400,
 
where f′ 2  is the focal length of the second lens group and f′ is the total focal length of the objective  1 .
 
   The cemented component of the second lens group meets the condition:
 
10 −8   *f′   2 +9*10 −8   *f′− 1.8*10 −4 ≦1/ f   1 /ν e1 +1/ f   2 /ν e2 ≦10 −8   *f′   2 +9*10 −8   *f′− 10 −4 ,
 
and the lens ( 2 . 1 ) of the lens group meets the condition ν e3 ≦55, where f′ 1  is the focal length of lenses  2 . 22 , f′ 2  is the focal length of lenses  2 . 21 , f′ is the total focal length of the objective, ν e1  and ν e2  are the Abbe numbers of lenses  2 . 22  and  2 . 21 , and ν e3  is the Abbe number of lens  2 . 1 .
 
   This fourth construction of the objective is distinguished above all in that it is apochromatically corrected and also has a high transmission in the near UV spectral region. 
   While the foregoing description and drawings represent the present invention, it will be obvious to those skilled in the art that various changes may be made therein without departing from the true spirit and scope of the present invention.