US 12,342,984 B2
Objective optical system, image pickup apparatus, and endoscope
Ippei Sakurada, Kunitachi (JP)
Assigned to OLYMPUS CORPORATION, Tokyo (JP)
Filed by OLYMPUS CORPORATION, Hachioji (JP)
Filed on Aug. 12, 2022, as Appl. No. 17/887,356.
Application 17/887,356 is a continuation of application No. PCT/JP2020/008662, filed on Mar. 2, 2020.
Prior Publication US 2023/0055267 A1, Feb. 23, 2023
Int. Cl. A61B 1/00 (2006.01); G02B 3/04 (2006.01); G02B 23/24 (2006.01)
CPC A61B 1/00096 (2013.01) [G02B 3/04 (2013.01); G02B 23/243 (2013.01)] 12 Claims
OG exemplary drawing
 
1. An objective optical system comprising, in order from the object side to the image side:
a positive front lens group; and
a positive rear lens group,
wherein focusing is performed by moving the front lens group along the optical axis,
the front lens group includes, in order from the object side, a negative first lens, a positive second lens, an aperture stop, and a positive third lens, as lenses having refractive power,
the rear lens group includes, in order from the object side, a positive cemented fourth lens and a positive fifth lens having a convex surface facing toward the object, and
the objective optical system satisfies the following conditional expression (1):
0.35<FL/Ff<0.85  (1)
where Ff is the focal length of the front lens group, and FL is the focal length of the entire objective optical system in a normal observation state.