Patent ID: 10809521

Abstract:
An endoscope objective optical system consists of a front group having a negative refractive power, an aperture stop, and a rear group having a positive refractive power. The front group consists of a first lens having a negative refractive power, and a second lens having a positive refractive power, and the rear group consists of a third lens having a positive refractive power, a cemented lens of a fourth lens having a positive refractive power and a fifth lens having a negative refractive power, and a sixth lens having a positive refractive power. An object-side surface of the first lens is a flat surface, and the second lens has a meniscus shape with a convex surface directed toward an image side, and the sixth lens is cemented to an image pickup element, and the following conditional expression (1) is satisfied: −1.2≤D6/F12≤−0.47  (1).