For determining pinhole designer, I prefer PinholeDesigner from A user constant of 1.4 seems to work better than the default 1.9 Lord Rayleigh constant. Lord Rayleigh may have calculated pinholes on a basis of scientific theory, not photographic results. Contrary to some photographers, the accuracy required for optimum performance is fairly critical. It seems counter-intuitive, but an optimum sized pinhole can actually resolve line pairs on a resolution chart with a spacing finer than the pinhole diameter. When comparing lens resolution charts photographed through pinholes, a deviation from optimum diameter by maybe 10% starts to become noticable. However, lens resolution charts don't make the most pleasing subject for pinhole photography. If detailed pinhole images are the goal, large film with short focal lengths gives the best results in the center of the image. Resolution and illumination fall off towards the corners. For a comprehensive book on pinhole photography, get Pinhole Photography by Eric Renner. For much online information, google for Jon Grepstad