An optical projection lens system for microlithography comprising in the direction of propagating radiation: a first lens group having positive refractive power, a second lens group having negative refractive power and comprising a waist (constriction) with a minimum diameter of the propagating radiation,...http://www.google.com/patents/US20040201899?utm_source=gb-gplus-sharePatent US20040201899 - Optical projection lens system
