The Measurement of Comatic Aberrations by Interferometry

Abstract

The path differences from point to point between an optical wave front and its mirror image are antisymmetrical with respect to the common line about which the inversion of the mirror image has occurred. Features of the wave front which depend only on even powers of the distance from the common line disappear, while features which depend on odd powers of the distance are doubled. Thus by suitable choice of the common line the comatic errors and the distortion in the wave front may be shown up independently of the effects of change of focus, spherical aberration, astigmatism and field curvature. The analysis may be carried out on interferograms made by comparison with a known reference wave front, or by the use of the interferometer described, which compares the wave front with its own mirror image directly. This interferometer may also be used as a shearing interferometer.