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1. (WO2018042797) OBJECTIVE OPTICAL SYSTEM FOR ENDOSCOPE

Pub. No.:    WO/2018/042797    International Application No.:    PCT/JP2017/020692
Publication Date: Fri Mar 09 00:59:59 CET 2018 International Filing Date: Sat Jun 03 01:59:59 CEST 2017
IPC: G02B 13/04
Applicants: OLYMPUS CORPORATION
オリンパス株式会社
Inventors: TSUJI Yoshifumi
辻善文
Title: OBJECTIVE OPTICAL SYSTEM FOR ENDOSCOPE
Abstract:
Provided is a high-performance objective optical system for an endoscope, which is compact, provides sufficient observation depth, has a wide viewing angle, and facilitates the observation and diagnosis of a lesion. This objective optical system for an endoscope comprises, in order from the object side: a front group FL having negative refractive power; an aperture stop S; and a rear group RL having positive refractive power. The front group FL has, in order from the object side: a first lens L1 comprising a negative single lens; and a second lens L2 comprising a positive single lens. The rear group RL has: a third lens L3 comprising a positive single lens; a cemented lens CL1 consisting of a positive fourth lens L4 and a negative fifth lens L5; and a positive sixth lens L6. The objective-side surface of the first lens L1 is a flat surface, the second lens L2 has a meniscus shape having a convex surface facing the image side, the sixth lens L6 is joined to an image capturing element IMG, and the following conditional expression (1) is satisfied: -1.2 ≤D6/F12 ≤-0.47 ... (1), where D6 is the thickness of the sixth lens L6, and F12 is the composite focal length from the first lens L1 to the second lens L2.