Patent ID: 9622652
Date: 2017-04-18
CPC Classifications: A61B,G02B

Claim:
1. An endoscope objective optical system used for underwater observation comprising: a front group having a negative refractive power, a brightness diaphragm, and a back group having a positive refractive power in order from an object side, wherein the back group is composed of three groups, all of the three groups having the positive refractive power; the front group is composed of a first group having a negative refractive power and a second group having a negative refractive power; the first group is a first lens which is a single lens; the second group is a single lens or a cemented lens; and conditional expressions below are satisfied: where Iw is a maximum image height in the underwater observation, ft is a focal distance of an entire objective optical system in observation in the air, Ia is a maximum image height of a principal ray that is capable of being transmitted through an objective optical system during the observation in the air, DL 1 is an outer diameter of the first lens, RL 1 a is a radius of curvature of an object side surface of the first lens, and fL 1 is a focal distance of the first lens.