| 摘要 |
The invention provides a liquid-immersion objective optical system including a first lens group and a second lens group. The first lens group includes a first lens component having positive refractive power, an object side thereof being a flat surface and a convex surface thereof facing an image-plane side; a second lens component having positive refractive power, a convex surface thereof facing the image-plane side; a third lens component having positive refractive power as a whole, formed by cementing a biconvex positive lens and a negative lens; and a fourth lens component formed by cementing a negative lens and a biconvex positive lens. The second lens group includes a fifth lens component formed by cementing a lens having a concave surface facing the object side and a lens having a convex surface facing the image-plane side; a sixth lens component having positive refractive power; and a seventh lens component having negative refractive power. The focal length F 1 of the entire first lens group, the magnification M of the objective optical system, the distance LT between the object plane and the image plane, and the distance LG between the object side of the first lens component L 1 and the image side of the fourth lens component L 4 satisfy the following conditional expressions: <?in-line-formulae description="In-line Formulae" end="lead"?>0.2<|M.F 1 /LT|<0.45<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>0/2<|LG 1 /LT|<0.4<?in-line-formulae description="In-line Formulae" end="tail"?>
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