Objective optical system for endoscope

摘要

A small-sized objective optical system for an endoscope having in order from an object side, a first negative lens which is planoconcave, a second meniscus lens having a convex surface directed toward an image side, a third positive meniscus lens having a convex surface directed toward the object side, a positive lens unit, and a cemented lens in which, a positive lens and a negative lens are cemented. Focusing is carried out by moving the third positive meniscus lens along an optical axis, and the second meniscus lens is a negative lens.

主权项

1. An objective optical system for an endoscope comprising in order from an object side:
a first negative lens which is planoconcave; a second meniscus lens having a convex surface directed toward an image side; a third positive meniscus lens having a convex surface directed toward the object side; a positive lens unit; and a cemented lens in which, a positive lens and a negative lens are cemented, wherein focusing is carried out by moving the third positive meniscus lens along an optical axis, and the second meniscus lens is a negative lens, and wherein negative and positive refers to a refractive power, and the objective optical system for endoscope satisfies the following conditional expression (1), and satisfies at least one of the following conditional expressions (4-1) and (4-2)
2.3≦fp/Ih≦5  (1)−1.5≦r2/r3≦−0.28  (4-1)−0.2≦r2/r4≦−0.08  (4-2) where, fp denotes a focal length of the positive lens unite and Ih denotes the maximum image height of the objective optical system for endoscope, r2 denotes an image-side radius of curvature of the first negative lens, r3 denotes an object-side radius of curvature of the second meniscus lens, and r4 denotes an image-side radius of curvature of the second meniscus lens.