Patent ID: 7046450

Claim:
A liquid-immersion objective optical system comprising: a first lens group; and a second lens group, the first lens group including a first lens component having positive refractive power, wherein an object side thereof is a flat surface and a convex surface thereof faces an image-plane side; a second lens component having positive refractive power, wherein a convex surface thereof faces 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 including a fifth lens component formed by cementing at least 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, wherein the liquid-immersion objective optical system satisfies conditional expressions (1) and (2) 0.2 <|M·F 1 /LT |<0.45 (1) 0.2 <|LG 1 /LT |<0.4 (2) wherein F 1 is the overall focal length of the first lens group, M is the magnification of the liquid-immersion objective optical system, LT is the distance from an object plane to the image plane, and LG 1 is the distance from the object side of the first lens component to the image side of the fourth lens component.