Patent ID: 7907352

Claim:
An endoscope objective lens comprising, in order from an object side: a negative first lens having a concave surface directed to an image side; a first cemented lens formed by cementing a second lens and a third lens, one of the second and third lenses being positive and, the other being negative; a stop; a positive fourth lens including a flat surface or a surface having a larger absolute value in radius of curvature, directed to the object side; and a second cemented lens formed by cementing a positive fifth lens and a negative sixth lens in order from the object side, the second cemented lens having a positive refractive power as a whole, wherein the endoscope objective lens satisfies the following conditional expressions (1) and (2) f 2 ×  v 5 - v 6   R A  × ( Bf + d 6 / n 6 ) > 10 ( 1 ) Bf/f> 2.5 (2) ν 6 <20 (6) where f denotes a focal length of the entire system, Bf denotes an air-equivalent length of a back focal length of the entire system, ν 5 denotes an Abbe number of the fifth lens, ν 6 denotes an Abbe number of the sixth lens, R A denotes a radius of curvature of a cemented surface between the fifth and sixth lenses, d 6 is a center thickness of the sixth lens, and n 6 is an index of refraction of the sixth lens.