Patent ID: 9684152
Date: 2017-06-20
CPC Classifications: A61B,G02B

Claim:
1. An endoscope objective optical system comprising: a lens group having negative optical power; a brightness diaphragm; and a lens group having positive optical power in order from an object side to an image side, wherein the lens group having negative optical power consists of a first lens having negative optical power, a second lens having negative optical power, and a third lens having positive optical power in order from the object side to the image side, the second and third lenses are cemented to each other to form a first cemented lens, and wherein the lens group having positive optical power has a second cemented lens in which at least one positive lens and at least one negative lens have been cemented to each other, and wherein when optical power of the first lens is represented as PW_f1, and combined optical power of the second and third lenses is represented as PW_f2, the following conditional expressions (1), (2), (5)′ and (6) are satisfied: where, D3(96 deg) is a distance in which a chief ray of a d-line entering the first lens at an angle of 96 degrees with respect to an optical axis of the objective optical system travels from an object side surface of the third lens to an image side surface of the third lens along the optical axis, and f_all is a focal distance of the whole system, 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 second lens, and Nd2 is a refractive index of a d-line of the second lens.