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1. (WO2018123847) ENDOSCOPE SYSTEM

Pub. No.:    WO/2018/123847    International Application No.:    PCT/JP2017/046079
Publication Date: Fri Jul 06 01:59:59 CEST 2018 International Filing Date: Sat Dec 23 00:59:59 CET 2017
IPC: G02B 13/04
A61B 1/00
G02B 23/26
Inventors: KATAKURA Masahiro
Provided is an endoscope system having an objective optical system capable of satisfactorily correcting lateral chromatic aberration and also capable of satisfactorily correcting off-axis aberration, particularly field curvature. The endoscope system has an objective optical system OBL, an optical path dividing section 20 for obtaining two optical images with different focuses, an image pickup element 22 for acquiring an optical image, and an image combining processing section 23c. The objective optical system OBL is composed of a fixed negative first lens group G1, a movable positive second lens group G2, and a fixed positive third lens group G3 in this order from the object side. By moving the second lens group G2 toward the image side, switching between normal observation and proximity observation can be performed. In the objective optical system, the first lens group G1 has a negative first lens L1 and at least one positive lens L4 in this order from the object side. The objective optical system satisfies the following conditional expressions (1) and (2). Expression (1): 1.3 < D_2T/fw < 5 Expression (2): 1.01 < ω(wide)/ω(tele) < 3.0