Patent ID: 11857158
Assignee: OLYMPUS CORPORATION
Field: Medical technology (Instruments)
Classification: CPC A  G | IPC A  G

Claim 0:
1. An optical system comprising in order from an object side:
an objective optical system;
a quarter-wave plate including one birefringent material, wherein a first axial astigmatism occurs in the quarter-wave plate;
a polarizing beam splitter is configured to split light from the objective optical system into a transmitted light and a reflected light, wherein a second axial astigmatism occurs in the polarizing beam splitter; and
an image sensor configured to pick up a first image of the transmitted light and a second image of the reflected light,
wherein:
the second axial astigmatism reduces the first axial astigmatism, and
the following conditional expression (1) is satisfied:

1.1≤Fno/(d/|Δn|)≤49  (1)

where:
Fno denotes an effective F-number of the objective optical system,
d denotes a thickness of the quarter-wave plate, and
Δn denotes a birefringence of the quarter-wave plate for an e-line, provided that |0.01|<Δn.