Abstract:
A microscope illuminator having three lenses with the center lens having an axially-symmetrical aspheric rear surface provides good lateral color correction for illuminated fields to 20mm. when used with a condenser having good color correction.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an improved microscope illumination system, and in particular to a transmitted light system which provides Kohler illumination for standard 10X through 100X objectives for up to a 20mm. field. Use of the proper &#34;throw-in&#34; lens extends the coverage down to 2.5X objectives for up to a 20mm. field. Those skilled in the art can select and position such a lens. 
     This system is designed as a simplified replacement for more complex transmitted light systems designed to illuminate a field of more than 20mm. The present system provides a lateral color-free image of the field iris when used with a condenser of the appropriate focal length and color correction. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION AND DRAWING 
     The present invention is an uncomplex illumination system for a microscope designed to provide illumination when a field of 20mm. or less is satisfactory. The use of a long focal length collimator provides lateral color-free imaging of the field iris when a condenser of good color correction is used. The illumination system operates as follows: Filament F0 is imaged at infinity by collector I. The collimator II reimages the filament in the region of condenser front pupil plane F2. At the same time, collimator II provides an image of field iris F1 at infinity. This system is thus designed for use with an infinity corrected condenser. 
     FIG. 1 is an optical diagram of the illumination system of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, the system comprises a front collector group I and adjacent filament F0. Rearward of and optically aligned with collector group I is the field iris F1. Rearmost, and also optically aligned, is the collimator II. 
     The five optically aligned components of the system designated A, B, E, F0 and F1. Mirror M is optional and is used when it is desired to minimize the vertical distance for the system. Collector group I comprises plano-concavo positive singlet A and concavo-convex positive singlet B. The rearmost surface of singlet B, having radius R 4 , is parabolic. Collimator II comprises plano-concavo positive singlet E. Flat mirror M may be used to divert light 90 degrees. With respect to the lens parameters, the axial thicknesses of successive lens elements are designated T 1  to T 3 , and the successive axial spaces from the filament plane (designated F0) are S 1  to S 6 . The successive lens radii are designated R 1  to R 6  where the minus sign (-) applies to surfaces whose center of curvature lies on the filament side of their vertices. The refractive indices and Abbe numbers of the glasses in the successive lenses are designated ND 1  to ND 3  and ν 1  to ν 3  respectively. 
     Since the numerical aperture and size of the illuminating spot at the object focal plane is directly proportional to the focal length of the condenser, lens parameters are given in Table I in terms of condenser focal length F, which typically varies from about 9.3 to 12.3mm. 
     
                                           TABLE I__________________________________________________________________________                     Index of AbbeLens   Radius  Thickness             Spacing Refraction                              Number__________________________________________________________________________              S.sub.1 =0.47619F   R.sub.1 =∞A          T.sub.1 =0.4762F                     1.51&lt;ND.sub.1 &lt;1.53                               ##STR1##   R.sub.2 =-0.87362F              S.sub.2 =0.51714F   R.sub.3 =-5.8514FB          T.sub.2 =0.8762F                     1.51&lt;ND.sub.2 &lt;1.53                               ##STR2##   R.sub.4 =-1.1899F             S.sub.3 =3.1857F             S.sub.4 =7.6590F   R.sub.5 =∞E          T.sub.3 =0.6667F                     1.51&lt;ND.sub.3 &lt;1.53                               ##STR3##   R.sub.6 = 4.5247F             S.sub.5 = 11.7143F__________________________________________________________________________ 
    
     The surface of lens B having radius R 4  is an axially-symmetrical, aspheric surface with axis of rotation Z. The value of Z for any given value of x and y is defined by the equation: ##STR4## wherein: d,e,f and g are zero 
     p 2  = x 2  + y 2   
     c = 1/R 4 , and 
     k = -1.0 
     The numerical values, in millimeters except for ND and ν, for a preferred embodiment for use with a condenser having a focal length F of 10.5mm. are given in Table II. 
     
                                           TABLE II__________________________________________________________________________                   Index of                          AbbeLens   Radius  Thickness            Spacing                   Refraction                          Number__________________________________________________________________________            S.sub.1 =5.00   R.sub.1 =∞A          T.sub.1 =5.00                   ND.sub.1 =1.523                           ##STR5##   R.sub.2 =-9.173            S.sub.2 =5.43   R.sub.3 =-61.440B          T.sub.2 =9.20                   ND.sub.2 =1.523                           ##STR6##   R.sub.4 =-12.494*            S.sub.3 =33.45            S.sub.4 =80.42   R.sub.5 =∞E          T.sub.3 =7.00                   ND.sub.3 =1.523                           ##STR7##   R.sub.6 =-47.510             S.sub.5 =123.00__________________________________________________________________________ *Aspheric surface having conic coefficient of -1.0.