Patent ID: 8305556

Claim:
A projection optical system with at least one catadioptric system, wherein the catadioptric system is an optical system which projects an image of a first plane onto a second plane, and wherein the catadioptric system comprises: a concave reflecting mirror disposed in an optical path between the first plane and the second plane; a first lens unit disposed in an optical path between the first plane and the concave reflecting mirror and having a positive refracting power; a first path deflecting surface disposed in an optical path between the first lens unit and the concave reflecting mirror and adapted to deflect the optical path; a second lens unit disposed in an optical path between the first path deflecting surface and the concave reflecting mirror; a second path deflecting surface disposed in an optical path between the second lens unit and the second plane and adapted to deflect the optical path; and a third lens unit disposed in an optical path between the second path deflecting surface and the second plane and having a positive refracting power; the projection optical system satisfying the following condition: 1 <FPG 3 /FPG 1<2.5, where FPG1 is a focal length of the first lens unit and FPG3 is a focal length of the third lens unit.