The shrink roadmap of semiconductors results in tighter specification of the wafer structures. Besides technological advancement and tighter tolerances for mask and scanner technology, it also requires an improvement of the numerical- and modeling accuracy of lithography simulation and proximity correction software. The modeling of high NA polarization effects and reflections within the resist stack are taken into account by current simulation models. Tool vendors support modeling accuracy by characterizing optical parameters of the scanners by measurement of the lens aberrations and the illumination pupil. The goal of this paper is to provide an algorithm, which allows achieving higher numerical accuracy by being able to use bitmaps with higher resolution for lens and illumination pupil at reasonable computational speed. While the focus of this paper is on optical lithography, the method itself is also of interest for the simulation of scanning laser microscopy such as optical disks or mask inspection.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.