| 摘要 |
PROBLEM TO BE SOLVED: To apply magnification of an objective lens as it is without changing observation magnification so much even when an operation distance of the objective lens is changed. SOLUTION: The focus adjustment unit 1 includes a front group optical system G<SB>1</SB>and a rear group optical system G<SB>2</SB>arranged on an optical axis between an objective optical system 12 condensing light from a sample A and an imaging optical system 11 imaging light condensed by the objective optical system 12 at a predetermined position, and arranged in order in an optical axis direction from a front side when setting its objective optical system 12 side as the front side and its imaging optical system 11 side as a rear side, and also equipped with a lens driving means 23 relatively moving the optical systems G<SB>1</SB>and G<SB>2</SB>in the optical axis direction, wherein the signs of refractive power of the optical systems G<SB>1</SB>and G<SB>2</SB>are different, and absolute values of focal lengths thereof are nearly equal to each other. COPYRIGHT: (C)2009,JPO&INPIT
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