| 摘要 |
It is possible to use the magnification of an objective lens as is, substantially without changing the observation magnification, even when the working distance of the objective lens is changed. The invention provides a focus-adjusting unit disposed on an optical axis between an objective optical system that collects light from a specimen and an image-forming optical system that images the light collected by the objective optical system at a prescribed position, comprising a front optical system and a back optical system, sequentially disposed along the optical axis direction from a front side, with the objective optical system serving at the front side and the image-forming optical system at the back; and a lens driving part that relatively moves these optical systems in the optical axis direction, wherein the front optical system and the back optical system have refractive powers of different sign and focal lengths of substantially equal absolute value.
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