Abstract:
The invention is directed to a high-aperture optical imaging system, particularly for microscopes, which comprises an objective and a tube lens unit and in which the objective has a magnification of less than or equal to 40× and a numerical aperture of greater than or equal to 1.0 and is chromatically corrected up to the infrared.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority of German Application No. 10 2005 051 025.6, filed Oct. 21, 2005, the complete disclosure of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     a) Field of the Invention  
         [0003]     The invention is directed to a high-aperture optical imaging system, particularly for microscopes, and relates primarily to a high-aperture immersion objective with apochromatic correction within a broad wavelength range. The imaging system has a large image field.  
         [0004]     b) Description of the Related Art  
         [0005]     Objectives with a lower magnification have a larger visual field and a numerical aperture that is generally lower. One of the main reasons for this is the dominance of visual observation in the microscope. However, since the resolving capacity of the human eye is limited, it does not make sense to furnish lower- and medium-magnification objectives with a high aperture. The gain in resolution achieved through a high aperture cannot be perceived by the human eye. Further, it is simpler in technical respects for a high-magnification objective to be outfitted with a high aperture than for a low-magnification objective because objectives of high magnification image only relatively small object fields.  
         [0006]     Accordingly, objectives with a high numerical aperture traditionally also have high magnifications. An immersion objective with a magnification of 100× and a numerical aperture up to 1.65 is described in U.S. Pat. No. 5,659,425. Immersion objectives with a high numerical aperture and low magnification are not realized.  
         [0007]     In recent times, visual observation has diminished in importance in many fields and applications and other channels of image recording have become increasingly important. These channels often possess the possibility of post-magnification which allows full exploitation of the resolving capacity of the objective. Therefore, in applications of this kind it is reasonable to work with objectives having both a lower magnification and a high aperture because a low magnification is equivalent to a large object field and, consequently, the frequently cumbersome changing of objectives can be dispensed with.  
         [0008]     U.S. Pat. No. 5,982,559 describes an immersion objective for microscopes which comprises eight lens groups, has a numerical aperture of 1.3, a magnification of 40× and a flat image field and in which optical errors are extensively corrected. However, this objective has no apochromatic correction, particularly up to the infrared spectral region. Yet this characteristic is increasingly desirable in connection with two-photon applications.  
       OBJECT AND SUMMARY OF THE INVENTION  
       [0009]     Accordingly, it is the primary object of the invention to provide a high-aperture optical imaging system for microscopes, particularly with an immersion objective, also for low magnifications, which has a large image field and apochromatic correction.  
         [0010]     According to the invention, this object is met in an optical imaging system, in accordance with the invention, particularly for microscopes, which comprises an objective and a tube lens unit. The objective has a magnification of less than or equal to 40× and a numerical aperture of greater than or equal to 1.0 and is chromatically connected up to the infrared.  
         [0011]     In a particularly advantageous solution, the objective of the optical imaging system comprises: 
        a first partial system (T 1 ) which has, in order from the object side, a first individual lens or has a first cemented doublet and a second individual lens and third individual lens, wherein the second individual lens and third individual lens have a total refractive power of 0.14 D to  024  D,     a second partial system (T 2 ) which is formed of a cemented triplet with a maximum refractive power of 0.06 D and a second cemented doublet with a refractive power of 0.12 D to 0.2 D,     and a third partial system which comprises a cemented doublet and an individual lens or an individual lens and a meniscus formed as a cemented component or two menisci formed as cemented components, wherein, considered from the object side, the first meniscus conforms to the relationship 0.0045&lt;−D*D k &lt;0.0059, and the second meniscus has essentially no refractive power, where D is the total refractive power of the objective and D k  is the refractive power of the first meniscus of the third partial system (T 3 ).        
 
         [0015]     It is advantageous when the first cemented doublet has the shape of a meniscus which is concave toward the object and has a magnification factor of 1.73 to 1.81.  
         [0016]     Further, an individual lens is provided in the first partial system instead of the first cemented doublet and the following two individual lenses are made of crown glass or CaF 2 .  
         [0017]     It is also advantageous when the cemented triplet of the second partial system comprises a central lens with negative refractive power made of short flint glass and two lenses with positive refractive power made of fluor crown glass or CaF 2 .  
         [0018]     The second cemented doublet of the second partial system advantageously comprises a lens with negative refractive power made of short flint glass and a lens with positive refractive power made of fluor crown glass or CaF 2 .  
         [0019]     It is likewise advantageous that the first meniscus of the third partial system is formed as a cemented component or individual lens.  
         [0020]     Further, it is advantageous that the concave surface of the two menisci of the third partial system are adjacent, i.e., face one another.  
         [0021]     The objective is followed by a tube lens unit as is disclosed in claim  8 . This tube lens unit can advantageously comprise a lens with positive refractive power and an optical element without refractive power. Further, the tube lens unit can also comprise two cemented doublets and an optical element without refractive power which is advantageously made of BK7 glass.  
         [0022]     The invention will be described more fully in the following with reference to an embodiment example. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     In the drawings:  
         [0024]      FIG. 1  shows the construction of an optical system according to the invention with objective and tube lens unit;  
         [0025]      FIG. 2  shows a lens arrangement of an objective with high aperture;  
         [0026]      FIG. 3  shows a lens arrangement of another objective;  
         [0027]      FIG. 4  shows the lens arrangement of a tube lens unit; and  
         [0028]      FIG. 5  shows the lens arrangement of another tube lens unit; and  
         [0029]      FIG. 6  schematically illustrates the chromatic correction of an objective according to the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]      FIG. 1  shows the basic construction of an optical system, according to the invention, which comprises a high-aperture objective  1  which is ale for use with an immersion liquid and, downstream of the latter on the image side, a tube lens unit  2  with an optical element  3  without refractive power. The objective itself comprises a plurality of individual lenses and/or lens groups which are assembled in partial systems T 1 , T 2  and T 3 . The lens groups are constructed as cemented doublets or cemented triplets.  
         [0031]     The tube lens unit  2  shown in  FIG. 1  advantageously comprises cemented doublets  2 . 1  and  2 . 2  or a lens and an optical element  3  without refractive power which is arranged downstream on the object side of the cemented components or the lens.  
         [0032]     The lens arrangement of a high-aperture objective  1  according to the invention shown in  FIG. 2  likewise has three partial systems T 1 , T 2  an T 3 . Considered from the object side, the first partial system T 1  comprises a cemented doublet with lenses L 0  and L 1  and the individual lens L 2  and the individual lens L 3 . Together, the individual lenses L 2  and L 3  have a total refractive power of 0.14 D to 0.24 D, where D is the total reactive power of the objective  1 . The individual lenses L 2  and L 3  are made of fluor crown or CaF 2 .  
         [0033]     The second partial system T 2  of this objective  1  comprises, in order, a cemented doublet with a maximum refractive power of 0.06 D formed of lenses L 4  and L 5  and a cemented triplet with a total refractive power of 0.12 D to 0.20 D comprising lenses L 6 , L 7  and L 8 . The negative lens L 4  of the cemented doublet is made of a short flint glass, and the positive lens L 5  of this cemented component is made of fluor crown glass or CaF 2 .  
         [0034]     The third partial system T 3  of this objective  1  comprises two menisci which are formed as cemented doublets and comprise lenses L 9  to L 12 . The first meniscus considered from the object side conforms to the relationship 0.0045&lt;−D*D k &lt;0.0059, and the following second meniscus has essentially no refractive power, where D k  is the refractive power of the first meniscus.  
         [0035]     The optical data of an objective constructed according to  FIG. 1  are shown in the following table:  
                                                     TABLE 1                               Thickness   Refractive   Abbe       Surface   Radius r   d   index n e     Number ν e                                  0           oil immersion           1   infinite   0.57   1.489   70.2       2   −0.668   3.4   1.820   46.4       3   −3.400   0.25       4   −12.771   2.95   1.530   76.6       5   −6.541   0.10       6   −180.409   3.10   1.530   76.6       7   −12.958   0.10       8   29.639   1.20   1.616   44.3       9   13.335   6.20   1.440   94.6       10   −17.529   5.17       11   42.475   2.90   1.440   94.6       12   −17.402   1.20   1.641   42.2       13   9.858   4.70   1.440   94.4       14   −19.248   0.10       15   7.606   4.80   1.498   81.0       16   −84.745   1.15   1.616   44.3       17   5.465   4.99       18   −12.230   1.38   1.561   53.8       19   7.829   3.52   1.602   37.8       20   −17.529                 magnification: 40×           numerical aperture: 1.3            coverslip thickness: 0.17 mm            working distance: 0.259 mm             
 
         [0036]      FIG. 4  shows a corresponding tube lens unit  2  which is arranged downstream of the objective  1  on the image side. It comprises a lens  4  with positive refractive power, which is arranged in the microscope beam path at a distance of 126.5 mm from the objective  1 , and an optical element  5  which has zero refractive power and is arranged at a distance d 0  of 60.0 mm from lens  4 . The data of this tube lens unit  2  are shown in Table 2.  
                                                           TABLE 2                           Tube lens unit data                    Thickness   Refractive   Abbe       Surface   Radius r   d   index n e     Number ν e                      0       126.5               1    189.417   10.9   1.582   53.6       2   −189.417   60       3   infinity   80   1.519   64.0       4   infinity   48.2       5   intermediate           image plane                    
         [0037]     The lens arrangement shown in  FIG. 3  for another high-aperture objective  1  according to the invention likewise-comprises the three partial systems T 1 , T 2  and T 3 . Considered from the object side, the first partial system T 1  comprises a first cemented doublet which has lenses L 1  and L 2  and which has the shape of a meniscus which is concave toward the object, and a second individual lens L 3  and third individual lens L 4 . The individual lenses L 3  and L 4  together have a total refractive power of 0.14 D to 0.24 D, where D is the total refractive power of the objective  1 . The individual lenses L 3  and L 4  are made of fluor crown glass or CaF 2 .  
         [0038]     The second partial system T 2  of this objective  1  according to  FIG. 3  comprises, in order, a cemented triplet with a maximum refractive power of 0.06 D which is formed of lenses L 5 , L 6  and L 7  and a cemented doublet with a total refractive power of 0.12 D to 0.20 D comprising lenses L 8  and L 9 . The cemented triplet comprises a central negative lens L 6  which is enclosed by positive lenses L 5  and L 7 . The maximum refractive power of this cemented triplet is 0.06 D. Lenses L 5  and L 7  are made of a short flint glass and fluor crown glass or CaF 2 , and lens L 6  is made of a short flint glass. The cemented doublet comprises a positive lens L 8  of fluor crown glass or CaF 2  and a negative lens L 9  of short flint glass.  
         [0039]     The third partial system T 3  of this objective  1  comprises a lens L 10  which is formed as a meniscus and a meniscus constructed as a cemented doublet comprising lenses L 11  and L 12 . The lens L 10  conforms to the relationship 0.0045&lt;−D*D k &lt;0.0059, and the following meniscus has essentially no refractive power, where D k  is the refractive power of lens L 10  in this embodiment example.  
         [0040]     The optical data of an objective constructed according to  FIG. 3  are shown in the following table:  
                                                     TABLE 3                               Thickness   Refractive   Abbe       Surface   Radius r   d   index n e     Number ν e                                  0           water immersion           1   −9.039   4.80   1.519   64.0       2   −19.248   4.61   1.597   35.0       3   −9.576   0.40       4   −101.598   5.00   1.440   94.6       5   −14.227   0.10       6   64.011   5.50   1.440   94.6       7   −21.754   0.50       8   58.715   7.00   1.530   76.6       9   −15.181   1.50   1.641   42.2       10   14.227   6.80   1.440   94.6       11   −53.084   0.10       12   14.539   7.10   1.440   94.6       13   −68.788   1.77   1.561   53.8       14   89.771   0.39       15   12.320   9.12   1.758   52.1       16   4.800   5.45       17   −6.587   4.51   1.519   64.0       18   10.441   11.62   1.530   76.6       19   −12.958                 magnification: 20            numerical aperture: 1.0            working distance: 2.149             
 
         [0041]      FIG. 5  shows a corresponding tube lens unit  2  which is arranged downstream of the objective  1  on the image side. This tube lens unit  2  comprises a cemented doublet, which is arranged in the microscope beam path at a distance from the objective  1  and which has a lens  6  with negative refractive power and a lens  7  with positive refractive power, and another cemented doublet having a lens  8  with positive refractive power and a lens  9  with negative refractive power and an optical element  10  which has zero refractive power and which is arranged at a distance do of 126.5 mm from lens  9 . The data of this tube lens unit  2  are shown in Table 4.  
                                                           TABLE 4                           Tube lens unit data                    Thickness   Refractive   Abbe       Surface   Radius r   d   index n e     Number ν e                      0       132               1   233.816   4   1.723   29.3       2   28.386   12   1.716   53.6       3   209.659   10.69       4   131.464   13   1.624   36.1       5   −27.189   4   1.623   60.1       6   −328.015   55.18       7   infinity   80   1.519   64       8   infinity   48.2       9   intermediate           image plane                    
         [0042]     The data of another objective which is constructed according to  FIG. 3  are given in the following Table 5.  
                                                     TABLE 5                               Thickness   Refractive   Abbe       Surface   Radius r   d   index n e     Number ν e                                              water immersion           1   −9.039   5.10   1.519   64.0       2   −18.040   4.25   1.725   34.5       3   −10.441   0.40       4   −77.181   5.00   1.440   94.6       5   −13.820   0.10       6   66.354   5.50   1.440   94.6       7   −21.442   0.50       8   44.990   7.20   1.530   76.6       9   −15.396   1.50   1.641   42.2       10   13.724   6.80   1.440   94.6       11   −81.166   0.10       12   14.331   8.00   1.440   94.6       13   −34.724   1.60   1.561   53.8       14   381.220   0.30       15   11.965   8.24   1.758   52.1       16   4.800   5.62       17   −6.587   4.50   1.519   64.0       18   10.667   11.67   1.530   76.6       19   −12.958                 magnification: 20            numerical aperture: 1.0            working distance: 2.15             
 
         [0043]     The associated tube lens unit is shown in  FIG. 5 . The data of the tube lens unit correspond to the values indicated in Table 4.  
         [0044]     The constructional data of another objective according to the invention which is not shown and which likewise comprises three partial systems are indicated in Table 6. In this case, the first partial system provided on the object side comprises a cemented doublet and two individual lenses. The second partial system which is arranged downstream on the image side comprises a cemented triplet and a cemented doublet. Downstream of the latter on the image side in the third partial system, there follows a cemented doublet and an individual lens.  
                                                     TABLE 6                               Thickness   Refractive   Abbe       Surface   Radius r   d   index n e     Number ν e                                              water immersion           1   −9.039   1.82   1.610   56.4       2   −24.052   6.69   1.725   34.5       3   −9.307   0.10       4   110.5977   5.50   1.440       5   −18.1711   0.30       6   58.2937   5.20   1.440   94.6       7   −22.712   0.50       8   51.2124   6.40   1.530   76.6       9   −15.732   1.50   1.641   42.2       10   14.433   7.40   1.440   94.6       11   −29.2156   0.10       12   12.496   7.49   1.440   94.6       13   −41.2689   1.60   1.561   53.8       14   29.8533   0.30       15   8.059   4.60   1.758   52.1       16   4.529   5.71       17   −5.662   2.62   1.525   59.2       18   9.173   11.04   1.530   76.6       19   −11.6472                 magnification: 20×           numerical aperture: 1.0            working distance: 2.152 mm             
 
         [0045]     The constructional data of the associated tube lens unit correspond to the values indicated in Table 2.  
         [0046]     The schematic representation of the chromatic aberration in  FIG. 6  shows that an objective according to the invention has very good correction in the near infrared, in this case, e.g., 800 nm.  
         [0047]     The invention is not limited to the embodiment examples shown herein. Further developments by a person skilled in the art do not constitute a departure from the protected field.  
         [0048]     While the foregoing description and drawings represent the present invention, it will be obvious to those skilled in the art at various changes may be made therein without departing from the true spirit and scope of the present invention.  
       REFERENCE NUMBERS  
       [0000]    
       
           1  objective  
           2  tube lens unit  
           3  optical element without refractive power  
           4  lens  
           5  optical element  
           6  to  9  lens  
           10  optical element  
          T 1  to T 3  partial systems  
          L 1  to L 2  lenses  
          r 1  to r 20  radii  
          d 1  to d 19  thicknesses  
          D total refractive power of the objective  
          D k  refractive power of the first meniscus of the third partial system