Patent ID: 11815739

Abstract:
An endoscope optical system includes, in order from an object side: a fixed negative first lens group; a movable positive second lens group; a fixed aperture stop; and a fixed positive third lens group, the endoscope optical system being capable of switching between a normal observation state and a magnified observation state by moving the second lens group along an optical axis, in which the third lens group includes, in order from the object side: a cemented lens consisted of three lenses; and a cemented lens consisted of two lenses. In the cemented lens consisted of three lenses, three lenses of a positive lens, a negative lens, and a positive lens are cemented. In the cemented lens consisted of two lenses, two lenses of a positive lens and a negative lens are cemented. The following conditional expressions (1) and (2) are satisfied: 1.70<(nd3G1+nd3G2+nd3G3)/3<2.0 (1); and 1.72<(nd3G4+nd3G5)/2<2.0 (2).