Quantitative methods for examining and describing the surfaces of off-axis parabolic mirrors are given, together with practical suggestions for the most effective use of such mirrors. Included are tests with, and without, an optical flat. In each case the theory and experimental procedure are illustrated by application to a particular mirror. The quality of a mirror is given in terms of the minimum slit width that can be profitably used with it.
L. G. SCHULZ, "Quantitative Tests for Off-Axis Parabolic Mirrors," J. Opt. Soc. Am. 36, 588-588 (1946)