Patent ID: 11931004
Assignee: OLYMPUS CORPORATION
Field: Optics (Instruments)
Classification: CPC A  G | IPC A  G

Claim 12:
13. An objective optical system comprising:
a first spherical lens and a second spherical lens that are arrayed in this order from an object; and
at least one of a first optical medium and a second optical medium;
an image transmission system that is disposed at the opposite side of the second spherical lens from the object,
wherein the first optical medium is a solid or liquid disposed at an object side of the first spherical lens and is in close contact with a surface on the object side of the first spherical lens, over an entire optical path; and
the second optical medium is a solid or liquid disposed at an opposite side of the second spherical lens from the object and is in close contact with a surface on the opposite side of the second spherical lens from the object, over the entire optical path;
a back focal point is located at the opposite side, from the object, of a surface on the object side of the second spherical lens;
the back focal point is located inside the second spherical lens;
the first spherical lens and the second spherical lens have radii identical to each other and are made of materials identical to each other;
a surface on the object side of the first optical medium is a flat surface perpendicular to the optical axis; and
the following conditional expression (1) is satisfied:

0≤{n1(2n3−n1)−n1LN}/{2n3−(n1−3n3)(n1−2)−(n1−1)LN}≤2  (1)

where
n1 indicates a refractive index of the first spherical lens and the second spherical lens,
R1 indicates a radius of the first spherical lens and the second spherical lens,
n3 indicates a refractive index of the first optical medium,
L indicates the interval on the optical axis between a surface on the opposite side of the first spherical lens from the object and the surface on the object side of the second spherical lens, and
N=(n1n3+n1−2n3)/R1.