PROBLEM TO BE SOLVED: To provide a variable power optical system for endoscope suitable for changing magnification into high magnification while keeping a constant observation distance at a telephoto end, while maintaining satisfactory optical performance at each variable power position from a wide angle end to the telephoto end.SOLUTION: In the variable power optical system which includes: a first lens group G1 having a first cemented lens CL1 formed by cementing a negative lens L1 turning its concave surface to an image side, a positive lens L2 turning its convex surface to the image side, a negative lens L3 and a positive lens L4, and has positive power a second lens group G2 having a second cemented lens CL2 formed by cementing a negative lens L5 and a positive lens L6, and has negative power and a third lens group G3 having a third cemented lens CL3 formed by cementing a positive lens L7, a negative lens L8 and a positive lens L9, and is an optical system for variably magnifying an optical image due to the movement of the second lens group, the focal lengths of the entire system and each group satisfy prescribed conditions.COPYRIGHT: (C)2012,JPO&INPIT【課題】広角端から望遠端までの各変倍位置で光学性能を良好に維持しつつ望遠端で一定の観察距離を保ちながら倍率を高倍率にするのに好適な内視鏡用変倍光学系を提供する。【解決手段】像側に凹面を向けた負レンズL1、像側に凸面を向けた正レンズL2、負レンズL3と正レンズL4とを接合した第一の接合レンズCL1を有する正のパワーを持つ第一のレンズ群G1と、負レンズL5と正レンズL6とを接合した第二の接合レンズCL2を有する負のパワーを持つ第二のレンズ群G2と、正レンズL7、負レンズL8と正レンズL9とを接合した第三の接合レンズCL3を有する第三のレンズ群G3とを有し、第二のレンズ群の移動によって光学像を変倍する光学系であり、全系及び各群の焦点距離を所定の条件を満たす。【選択図】図2
