Patent ID: 7688422

Claim:
An imaging optical system that make a first plane optically conjugate with a second plane, comprising: a first optically transparent member located nearest to the second plane, and a second optically transparent member located adjacent to the first optically transparent member, wherein an optical path between the first optically transparent member and the second plane is fillable with a first liquid, and wherein an optical path between the first optically transparent member and the second optically transparent member is fillable with a second liquid, the imaging optical system satisfying the following conditions: 1< D 1/( M 1 +M 2)<20, and 0.007< D 1 /D 2<0.05, where D1 is a center thickness of the first optically transparent member, M1 is a center thickness of a layer of the first liquid, M2 is a center thickness of a layer of the second liquid, and D2 is a sum of center thicknesses of all optically transparent members in the imaging optical system.