Patent ID: 8786955

Claim:
An endoscope objective optical system comprising in order from an object side: a first lens formed of a plano-concave lens having a concave surface facing an image side; a second lens formed of a plano-concave lens having a concave surface facing the object side; an aperture stop; and a third lens formed of a plano-convex lens having a plane surface facing the object side, the endoscope objective optical system satisfying the following conditional expressions (1) to (3): 0.7≦| fab/f|≦ 0.9 (1) 1.7≦| fe/fab|≦ 2 (2) 2≦ fb/fa≦ 4 (3) where f represents a focal length of the entire system, fa represents a focal length of the first lens, fb represents a focal length of the second lens, fe represents a focal length of the third lens, and fab represents a combined focal length from the first lens to the second lens.