| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an objective optical system for an endoscope, optimum for moving by reducing the diameter of a movable lens group in an objective optical system adapted to change the direction of a visual field in the midway of an optical path. Ž<P>SOLUTION: In this objective optical system for an endoscope, a diaphragm, a first lens and a second lens are disposed in order from the object side, and the first lens is formed of a positive meniscus lens whose concave surface is pointed toward the object. The second lens is formed of a positive lens whose convex surface is pointed toward the object. The objective optical system for an endoscope satisfies the following conditional expressions (1):-1.2<r1/f<0.8, (2):-1.0<r2/f<-0.6, (3): 2.1<f2/f<4.2, and (4): nd1>1.65, wherein r1 is an object side radius of curvature of a first lens, r2 is an object side radius of curvature of a second lens, f is a focal length of the whole system, f2 is a focal length of a second lens group, and nd1 is refractive index of d line of the first lens. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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