Abstract:
A microscope objective lens is constructed with fixed lens units having a numerical aperture NA which is 0.6≦NA≦&lt;0.8 and a magnification β which is 40≦β≦63, to observe a sample placed on a sample holding member and covered with a protective transparent member having a thickness t which is 0.1 mm&lt;t&lt;0.15 mm.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a transmission type illumination optical microscope, and in particular, to an objective lens used in this microscope and a method of using the microscope.  
           [0003]    2. Description of Related Art  
           [0004]    [0004]FIG. 1 shows a schematic structure of an example of a conventional transmission type illumination optical microscope. In this figure, reference numeral  1  represents an eyepiece;  2 , a lens barrel;  3 , a microscope frame;  4 , revolver attached to the lower portion of the lens barrel  2  through the microscope frame  3 ;  5 , an objective lens mounted to the revolver  4 ;  6 , a stage supporting section attached to the microscope frame  3  so that it can be raised and lowered;  7 , a lower stage retained on the stage supporting section  6  so that it can be moved along an X axis (or a Y axis) with respect to the stage supporting section  6 ;  8 , an upper stage retained on the lower stage  7  so that it can be moved in a direction perpendicular to the lower stage  7 , that is, along the Y axis (or the X axis) with respect to the stage supporting section  6 ;  9 , a surface illuminant fitted into the upper stage  8 ;  10 , a specimen;  11 , an upper stage control knob for moving the upper stage  8  with respect to the lower stage  7 ;  12 , a lower stage control knob for moving the lower stage  7 , together with the upper stage  8 , with respect to the stage supporting section  6 ; and  13 , a focusing knob for raising and lowering the stage supporting section  6  through the microscope frame  3 . The lower stage  7  and the upper stage  8  constitute a microscope stage. The specimen  10  is placed on the surface illuminant  9  through hard glass or sapphire glass and is held on the stage by a well-known clamp, not shown. Focusing is performed by turning the focusing knob 13, and when the stage control knob  11  or  12  is turned, the specimen  10  is moved in the X or Y direction. In this way, a desired observation is carried out.  
           [0005]    Consider the case of cytodiagnosis in which such a transmission type illumination optical microscope is used. The specimen  10 , as shown in FIG. 2, is made in such a way that cells of a sample are placed on a slide glass  10   a  (preparation) which is a sample holding member, and are covered with a glass cover  10   b  which is a protective transparent member, and thereby the sample is sealed between the sample holding member  10   a  and the protective transparent member  10   b . In this case, the protective transparent member  10   b  usually has a thickness of 0.17 mm, and it is common practice that the objective lens  5  used is corrected for spherical aberration in accordance with this thickness of the protective transparent member  10   b . For a dry objective lens which has a numerical aperture (NA) of 0.8 or more, in order to accommodate variations in thickness of the protective transparent member  10   b , some of protective transparent members are designed so that spherical aberration can be corrected, ranging in thickness from 0.1 to 0.2 mm.  
           [0006]    In recent years, high-speed and low-cost treatment in such cytodiagnosis and histodiagnosis has become necessary. Consequently, the high-speed preparation of the specimen  10  has also become necessary. This brings about the advent of an automatic sealing machine in which high-speed treatment of preparation of the specimen, namely sealing work of the sample, is realized (500-1000 pieces per hour). According to this machine, instead of the conventional glass cover used as the protective transparent member  10   b , a transparent macromolecular film (0.1 mm in thickness), for example, like cellulose acetate, to which an adhesive sealant is applied, is used and pressed against the sample holding member on which the sample is placed, to thereby obtain a protective transparent member with a thickness of approximately 0.12 mm, including the layer thickness (0.02 mm) of the sealant. When this specimen is observed through a common objective lens such as that mentioned above, observation is carried out in a state where spherical aberration is not completely corrected, and thus there is the problem that the actual state of the sample cannot be correctly analyzed. In order to solve this problem, it is conceivable to use an objective lens in which spherical aberration can be corrected with respect to a change in thickness of the protective transparent member, mentioned above. However, the objective lens of this type is very expensive and in addition, requires a manual operation for correction. Hence, the problem arises that not only does this cause an increase in treatment cost of cytodiagnosis or histodiagnosis, but it cannot completely meet the requirement for handling a large amount of specimens at a high speed.  
         SUMMARY OF THE INVENTION  
         [0007]    It is, therefore, an object of the present invention to provide a microscope objective lens which allows favorable and easy observation of the sample of a specimen provided with a protective transparent member having a thickness in a predetermined range, including a specimen made by the automatic sealing machine, and to provide a microscope using this objective lens and a method of using the microscope. In order to achieve this object, the microscope objective lens according to the present invention is constructed with fixed lens units having a numerical aperture NA which is 0.6≦NA≦0.8 and a magnification β which is 40≦β≦63, to observe a sample placed on the sample holding member and covered with the protective transparent member having a thickness t which is 0.1 mm&lt;t&lt;0.15 mm. The microscope according to the present invention includes a stage for supporting a sample placed on the sample holding member and covered with the protective transparent member having the thickness t which is 0.1 mm&lt;t&lt;0.15 mm; an objective lens constructed with fixed lens units having the numerical aperture NA which is 0.6≦NA≦0.8 and the magnification β which is 40≦β≦63, to form a magnified image of the sample; and an eyepiece for observing the magnified image of the sample formed by the objective lens.  
           [0008]    The method of using the microscope according to the present invention is to place the sample on the sample holding member and to cover the sample with the protective transparent member having the thickness t which is 0.1 mm&lt;t&lt;0.15 mm so that it is observed through the protective transparent member, the objective lens constructed with the fixed lens units having the numerical aperture NA which is 0.6≦NA≦0.8 and the magnification β which is 40≦β≦63, and the eyepiece.  
           [0009]    This and other objects as well as features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a side view showing a schematic structure of an example of a conventional transmission type illumination optical microscope;  
         [0011]    [0011]FIG. 2 is a perspective view showing an example of a specimen;  
         [0012]    [0012]FIG. 3 is a view showing a lens arrangement in a first embodiment of the microscope objective lens according to the present invention; and  
         [0013]    [0013]FIG. 4 is a view showing a lens arrangement in a second embodiment of the microscope objective lens according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    In accordance with the embodiments shown in the drawings, the present invention will be described below.  
         [0015]    The macromolecular film used as the protective transparent member  10   b  (see FIG. 2) in the automatic sealing machine described with reference to the prior art has a thickness of 0.1-0.15 mm in view of flatness and cost. In the embodiments of the present invention, a film with a thickness of 0.12 mm is employed, and two kinds of objective lenses constructed with fixed lens units in which spherical aberration is corrected in accordance with this thickness are provided to observe the specimen. In FIGS. 3 and 4, lens data of the objective lenses are as follows:  
                                                                                                     First embodiment       NA = 0.65  β = 40×            Surface   R   d   nd   Vd                       Specimen   ∞   0.1200   1.48749   70.23       protective       surface                       transparent                               member        1   ∞   0.8616        2   −1.64034   2.4300   1.78650   50.00        3   −2.50140   0.2600        4   30.63382   2.1800   1.49700   81.61        5   −5.46287   2.640000        6   35.24145   1.3700   1.84666   23.78        7   6.89344   3.0100   1.43875   94.97        8   −7.65820   24.5200        9   18.88750   3.4300   1.78650   50.00       10   −14.12677   1.5000   1.49831   65.03       11   7.54522   2.6744       12   ∞   50.0       13   56.90327   3.0000   1.48749   70.21       14   310.05549   0.3358       15   32.53850   6.0000   1.72342   37.95    {close oversize bracket}    Imaging lens       16   −87.52198   2.6000   1.71850   33.52       17   25.77751   151       Image plane   ∞                    Second embodiment       NA = 0.8  β = 60×            Surface   R   d   nd   Vd                       Specimen   ∞   0.1200   1.48749   70.23       protective       surface                       transparent                               member        1   ∞   0.3        2   −1.60604   2.9700   1.78650   50.00        3   −2.30350   0.540150        4   28.09533   3.3800   1.56907   71.30        5   −7.28858   1.2245        6   32.26382   0.8000   1.80518   25.43        7   5.78971   3.3500   1.43875   94.97        8   −7.57589   31.2779        9   18.71944   1.5000   1.76182   26.52       10   ∞   1.5000   1.52130   52.55       11   10.33604   −1.9665       12   ∞   50.0       13   56.90327   3.0000   1.48749   70.21       14   310.05549   0.3358       15   32.53850   6.0000   1.72342   37.95    {close oversize bracket}    Imaging lens       16   −87.52198   2.6000   1.71850   33.52       17   25.77751   151       Image plane   ∞                  
 
         [0016]    The objective lens of the first embodiment, as shown in FIG. 3, includes a front lens unit with a positive refracting power and a rear lens unit with a positive refracting power. The front lens unit is constructed with a meniscus lens directing its concave surface toward the specimen side, a biconvex lens, and a cemented doublet combining a concave lens and a convex lens. The rear lens unit is constructed with a cemented doublet combining a biconvex lens and a biconcave lens. A focal length f F  of the front lens unit is 4.87 mm and a focal length f R  of the rear lens unit is 342 mm. The ratio of the focal length between the front lens unit and the rear lens unit, f R /f F , is 70.2 in terms of an absolute value, and the refracting power of the rear lens unit is much smaller than that of the front lens unit.  
         [0017]    The objective lens of the second embodiment, as shown in FIG. 4, includes a front lens unit with a positive refracting power and a rear lens unit with a negative refracting power. The front lens unit is constructed with a meniscus lens directing its concave surface toward the specimen side, a biconvex lens, and a cemented doublet combining a concave lens and a convex lens. The rear lens unit is constructed with a cemented doublet combining a biconvex lens and a biconcave lens. The focal length f F  of the front lens unit is 5.3 mm and the focal length f R  of the rear lens unit is −393 mm. The ratio of the focal length between the front lens unit and the rear lens unit, f R /f F , is 68.5 in terms of an absolute value, and the refracting power of the rear lens unit, as in the first embodiment, is much smaller than that of the front lens unit.  
         [0018]    As mentioned above, the objective lens of the present invention has the front lens unit with a positive refracting power and the rear lens unit with a weaker refracting power than in the front lens unit. The front lens unit is provided with a meniscus lens directing its concave surface toward the specimen side, a convex lens, and a cemented doublet combining a concave lens and a convex lens. The rear lens unit is provided with a cemented doublet combining a convex lens and a biconcave lens. In this case, the objective lens satisfies a condition: |f R /f F &gt;68.  
         [0019]    In the lens data of the above embodiments, R represents the radius of curvature of the sample surface of the specimen, the surface of the protective transparent member, each of the lens surfaces, or the image plane; d represents the thickness of the protective transparent member, the thickness of each lens, or the air space between the lens surfaces; nd represents the refractive index of the protective transparent member or each lens in the d-line; and Vd represents the Abbe&#39;s number of the protective transparent member or each lens.  
         [0020]    For information, in the same specimen, an image of the specimen observed through an objective lens with the same magnification as in the first embodiment in which aberration is corrected in accordance with a protective transparent member with a thickness of 0.17 is visually compared with an image of the specimen observed through the objective lens of the first embodiment. In this case, the difference in resolution between both is not distinguished, but when these images are magnified fourfold for comparison, it is found that there is a considerable difference of resolution and the objective lens of the first embodiment brings about a better image. In the objective lens of either embodiment, a favorable image of the specimen is obtained when the thickness of the protective transparent member  10   b  ranges between 0.1 and 0.15 mm.  
         [0021]    At the present time, in the field of examination for cytodiagnosis and histodiagnosis, inexpensive objective lenses with a magnification of 40× and a numerical aperture of 0.65 are principally used. As will be obvious from the above description, the objective lens according to the present invention is capable of following this tendency and allows high-speed and low-cost treatment.