Patent ID: 7773318

Claim:
An objective optical system for endoscopes, characterized by comprising, in order from its object side, a stop, a first lens and a second lens, wherein the first lens comprises a positive meniscus lens concave on its object side and the second lens comprises a positive lens convex on its object side, with satisfaction of the following conditions (1), (2), (3) and (4): −1.2< r 1 /f <−0.8 (1) −1.0< r 2 /f <−0.6 (2) 2.1< f 2 /f <4.2 (3) nd1>1.65 (4) where r1 is a radius of curvature of an object-side surface of the first lens, r2 is a radius of curvature of an image-side surface of the first lens, f is a focal length of the whole optical system, f2 is a focal length of the second lens, and nd1 is a d-line refractive index of the first lens.