Null Ronchi Test for Aspherical Surfaces: Comment

P. B. Fellgett and A. E. Gee University of Reading, Reading, RG6 2AL, England. Received 16 October 1974.

We were interested in the recent paper by Malacara and Cornejo1 that describes a modification of the Ronchi test using a curved grating. An aspheric mirror under test may then yield a straight observed fringe test pattern.

Mobsby, who works independently at Shillings tone, Dor­set, has also used the technique for some six years in test­ing his figuring of aspheric mirrors. This is described by him in a regional astronomy journal.2

References 1. D. Malacara and A. Cornejo, Appl. Opt. 13, 1778 (1974). 2. E. Mobsby, Astronomy: J. Wessex Astron. Soc. 1, No. 3, 13

(1973).

February 1975 / Vol . 14, No. 2 / APPLIED OPTICS 279