Patent ID: 8102508

Claim:
An imaging optical system which conjugates a first surface to a second surface, comprising: a boundary lens that can be contacted with gas on a side of the first surface and that can be contacted with liquid on a side of the second surface, wherein the liquid has a refractive index larger than 1.5, and a refractive index of gas in an optical path within the imaging optical system is 1, wherein the boundary lens includes a positive refracting power and is made of an optical material including a refractive index larger than 1.7, and wherein a condition 0.11 <Yi/Fb< 0.15 is satisfied, where a focal length of the boundary lens is Fb and a maximum image height on the second surface in a case where the second surface is the image plane, or a maximum object height on the second surface in a case where the second surface is the object plane, is Yi.