Patent ID: 11903560
Assignee: OLYMPUS CORPORATION
Field: Medical technology (Instruments)
Classification: CPC A  G | IPC A  G

Claim 9:
10. An objective optical system comprising, in order from an object side:
a first group having a negative refractive power;
a second group having a positive refractive power; and
a third group having a positive refractive power,
wherein:
the first group and the third group are fixed and the second group is movable,
the first group includes at least two lenses having a negative refractive power,
the third group includes, in order from the object side, a 3-1st group having a positive refractive power, a 3-2nd group having a negative refractive power, a 3-3rd group having a positive refractive power, and a 3-4th group having a positive refractive power, and
the following conditional expressions (1)′″ and (7) are satisfied:

1.5≤Bk/f3≤6  (1)′″

−30≤f31/f1≤−3  (7)

where
Bk denotes a distance from a surface of the third group positioned nearest to an image to an image plane along an optical axis,
f3 denotes a focal length of the third group,
f31 denotes a focal length of the 3-1st group, and
f1 denotes a focal length of the first group.