Objective optical system

Abstract

The objective optical system consists of order from an object side, a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power, wherein focusing is carried out by moving the second group, and a lens nearest to image is a planoconvex positive lens having a convex surface directed toward the object side, and a flat surface of the planoconvex positive lens is either affixed directly to an image pickup surface or cemented to a cover glass formed on the image pickup surface, and the objective optical system satisfies the following conditional expression (1). 5<ff/f<8  (1) where, ff denotes a focal length of the planoconvex positive lens disposed nearest to image, and f denotes a focal length of the overall objective optical system at the time of normal observation.

Dependencies are inferred from the claim text.