Patent ID: 9459443
Filing Date: 2016-10-04
CPC Classification: A61B,G02B

Claim Text:
1. An endoscopic objective optical system comprising, in order from an object side to an image side, a front group provided with at least one first cemented lens having negative refractive power, a focusing lens provided with a second cemented lens or a single lens, and a rear group provided with positive refractive power, wherein: the front group and the rear group are always fixed on an optical axis; the focusing lens is provided to be moved along an optical axis; and the endoscopic objective optical system satisfies conditional expressions (1) to (4) below: where FB is back focus of the entire endoscopic objective optical system, the back focus being a distance from a lens surface of the rear group closest to the image side to a back focus position of the entire system, FL is a focal length of the entire endoscopic objective optical system, fc is a focal length of the focusing lens, |fc| is an absolute value of fc, F_F is a focal length of the front group, and F_R is a focal length of the rear group.