Patent ID: 7746571
Filing Date: 2010-06-29
Classification: G02B,G03F

Abstract:
1. An optical system comprising: an optical axis; a spherical concave reflection mirror; a lens group with positive refracting power arranged adjacent the mirror with an air space therebetween, the lens group comprising in order farthest from, to closest to, the mirror: a first plano-convex lens element having a convex surface facing the mirror and a flat surface facing away from the mirror; a negative meniscus lens element adjacent the first plano-convex lens and having a convex surface facing the mirror and a concave surface facing the first piano-convex lens element; a positive lens element adjacent the negative meniscus lens having a concave surface facing the negative meniscus lens and a convex surface facing the mirror; a negative double-concave lens element spaced apart far from the positive lens element and having a concave surface facing the positive lens and a concave surface facing the mirror; a second piano-convex lens element having a flat surface facing the negative double-concave lens element and a convex surface facing the mirror; a pair of prisms each having respective first and second surfaces, wherein the second surfaces are arranged adjacent the flat surface of the first piano-convex lens element on opposite sides of the optical axis, and wherein the first surfaces are arranged adjacent object planes and image planes, respectively; and wherein each lens element in the lens group and the pair of prisms provide chromatic aberration correction in a spectral region that contains at least g, h and i-line wavelengths.