| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system that is disposed on the rear side of an existing objective lens (on an image side) so that amount of spherical aberration caused by the change of the thickness or the like of cover glass can be optionally controlled, and to provide an optical observation device using the system. SOLUTION: The optical system is disposed on the image side of the objective lens, and a lens group L1 nearest to an object side has negative refractive power and a movable lens group G1 includes a doublet consisting of a positive lens and a negative lens. The spherical aberration is compensated by moving the movable lens group in the direction of an optical axis AX.
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