US Patent 7450312 Optical projection lens system

An optical projection lens system for microlithography includes in the direction of propagating radiation: a first lens group having positive refractive power, a second lens group having negative refractive power and a waist (constriction) with a minimum diameter of the propagating radiation, and a further lens arrangement with positive refractive power, which follows the second lens group. At least one lens of the projection lens system which is arranged in front of the waist includes an aspherical surface.