| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the unevenness of the brightness of observation field caused by the insufficiency of the peripheral light quantity of an illumination system by arranging a light quantity damping filter whose transmissivity is changed in a radial direction from the center orthogonally to an optical axis. SOLUTION: The transmissivity characteristic of an ND filter 5 functioning as the light quantity damping filter is set to obtain the darkness nearly the same as an outside dark area. The brightness of an observed image 7 is averagely lowered but the light quantity distribution of the entire field is nearly uniform both at the center part and the peripheral part, so that the insufficiency of the peripheral light quantity becomes inconspicuous. In the case of a microscope, it is desirable to arrange the ND filter 5 in the vicinity of an image position because the principal light beam angle of the image is small and axial luminous flux is largely overlapped on off-axis luminous flux as going away from the image. When the ND filter 5 is installed at the image position, the dust or the scratch of the filter is seen, so that it is good to arrange the ND filter 5 to be somewhat deviated from the image position. It is good to arrange the light quantity damping filter 5 is at or near a conjugate position to the sample 2 of an illumination system 1.
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