Aberration tolerances for visual optical systems*†

Abstract

The effects of aberrations on images formed by a total system, including the eye, are assessed in terms of modulation threshold, grating detectability, and modulation transfer functions. The effects of approximately one and two waves of third-order spherical aberration, coma, and astigmatism on the total system modulation transfer function are investigated using three-bar resolution targets and Ronchi rulings in two separate psychophysical experiments. The results of both experiments indicate that the experimentally determined system modulation transfer function is closely approximated by the theoretically calculated modulation transfer function of the total system optics (dioptrics included) in the presence of instrument aberrations. The data indicate that the eye accomodates of a "best focus" when spherical aberration and astigmatism (but not coma) are present in the instrument. The quantitative data are used to determine aberration tolerances for instruments that are designed for specific visual tasks and that employ simple targets similar to those investigated.