A multiple-beam interferometer that permits evaluation of autostigmatic systems is described. A small reference sphere is compared with a spherical wavefront in a manner analogous to the comparison of a plane wavefront with the reference flat in a Fizeau interferometer. To prevent walk-off of the fringes, a field lens is used at the center of curvature of the reference sphere. The instrument described has been used for evaluating spherical mirrors, concentric windows, and lenses.
L. R. Heintze, H. D. Polster, and J. Vrabel, "A Multiple-Beam Interferometer for Use with Spherical Wavefronts," Appl. Opt. 6, 1924-1929 (1967)