Method of and system for optimizing NURBS surfaces for an imaging system

A method of and program for optimizing NURBS optical surfaces for an imaging system. Preferably, the number and location of field point sources to be used in ray tracing of a NURBS modeled imaging system surfaces are determined by automatically iteratively increasing the number of field point sources during ray tracing until the spot size from adjacent field points sources on the image plane of the imaging system varies by less than a predetermined value. The number of rays for each field point source to be used in ray tracing of the NURBS modeled imaging system surfaces is preferably determined by automatically iteratively increasing the number of rays for each field point source during ray tracing until a predetermined number of rays intersect each NURBS rectangular grid sub-area. In ray tracing the modeled NURBS surfaces, the determined number and location of field point sources and the determined number of rays from each field point source are used and the grid control points of each NURBS surface are preferably iteratively adjusted, keeping symmetry or allowing freeform shapes, by means of an optimization algorithm based on ray tracing until spot sizes on the image plane meet a set requirement and/or until improvement in spot size is below a predetermined value.