and or to avoid relatively importantly small sub apertures on all optical surfaces except for the last optical surface closest to the image surface in certain embodiments of a computational routine designed to systematically avoid the occurrence of caustic condition on optical surfaces is now explained in connection with fig4 to 6 in a first step of the computational part of the manufacturing method a number of representative field points is defined ray tracing is performed for rays of ray bundles originating from those representative field points in a second step a pupil raster is defined where the pupil raster represents an array of raster points in a pupil surface of the projection objective where the raster points are spaced apart from each other in a two dimensional array at predefined distances in a third step ray trajectories of rays originating from the representative field points and passing through the raster points of the pupil raster are calculated for each of the representative field points for that purpose commercially available design programs such as code v oslo or zemax may be used the pupil raster typically encompasses the entire utilized aperture of the projection objective where the aperture determines the.