Patent ID: 6862078

Claim:
A projection optical system which projects an image of a first surface onto a second surface, and which has a lens component formed of fluorite and a lens component formed of silica, comprising: a first lens group including at least one lens component formed of fluorite and having a positive refractive power; a second lens group which is arranged in an optical path between the first lens group and the second surface and which has a negative refractive power; and a third lens group which is arranged in an optical path between the second lens group and the second surface and having a positive refractive power; wherein the projection optical system has no reflective surfaces in the optical path between the first surface and the second surface; and wherein when the number of the lens components formed of silica is Snum, the number of the lens components formed of fluorite is Cnum, and a numerical aperture of the second surface side of the projection optical system is NA, the following conditions are satisfied: Snum>Cnum ( 1 ) NA> 0 . 75 ( 2 ).