Patent ID: 9568725
Date: 2017-02-14
CPC Classifications: A61B,G02B

Claim:
1. An endoscope objective optical system comprising, in this order from an object side: a front group having negative refractive power as a whole; an aperture stop; and a rear group having positive refractive power as a whole, wherein the front group includes, in this order from the object side, a first lens, which is a single lens having negative refractive power, and a second lens, which is a single lens having positive refractive power, the rear group includes a third lens, which is a single lens having positive refractive power, a cemented lens formed of a fourth lens having positive refractive power and a fifth lens having negative refractive power, and a sixth lens having positive refractive power, an object-side surface of the first lens is a flat surface, the second lens has a meniscus shape, the sixth lens is joined to an image-acquisition element, and the endoscope objective optical system satisfies the following conditional expression: where Fno is the effective F number of the endoscope objective optical system, F 6 is the focal length of the sixth lens, and F 1 _ 5 is the composite focal length of the first to fifth lenses.