| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of stray light in operation of switching an objective lens at a dark field illumination time without using a dedicated shutter causing the increase of a cost, without introducing a light shielding method having a trouble in terms of durability, besides, without reducing the light of a light source itself. SOLUTION: At switching the observation method or the objective lens 18, an aperture diaphragm 14 is rotated only by the prescribed angle before operating the observation method or a motor-driven revolver 19, then, the vertical illumination light Q is shielded by the light shielding part of the aperture diaphragm 14, then, after switching the observation method or the objective lens 18, the aperture diaphragm is switched so that the diameter of the aperture diaphragm may correspond to the observation method or the objective lens 18.
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