Endoscope objective optical system

Abstract

The diameter of an endoscope insertion portion is reduced, and a wide field angle of an endoscope insertion portion is obtained. An endoscope objective optical system includes, 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, and satisfies 0.7≦|fab/f|0.9 1.7≦|fe/fab|≦2 2≦fb/fa≦4 where f: focal length of the entire system; fa: focal length of the first lens; fb: focal length of the second lens; fe: represents focal length of the third lens; fab: combined focal length from the first lens to the second lens.

Dependencies are inferred from the claim text.