... Previous experience with other space telescopes, and in particular the Hubble Space Telescope (HST), has shown that the ability to obtain groundbreaking discoveries relies heavily on the quality and understanding of the telescope s point spread function (PSF - the normalized image of an unresolved source). ... To lowest order the PSF of an imaging system is determined by two things: the shape and size of the effective entrance aperture (pupil) and the deviations from perfect optics across the pupil....