A simple and straightforward procedure for designing an aplanatic null lens, used in the testing of certain common convex ellipsoids and concave hyperboloids on a Fizeau interferometer, is described. In a conventional design the null lens aberrations are only reduced to some finite minimum which, depending on the asphere parameters and the design itself, may turn out to be significant. Using the proposed technique, which involves solving a set of simple equations, the determination of the parameters of an aplanatic null lens is readily achieved. The resulting null lens is nominally free of aberrations since each of the null lens surfaces transfers the analyzing wavefront aplanatically. Apart from gaining a more accurate means of evaluating aspherical lens surfaces, this reduction of aberrations results in a relaxation of otherwise tight null lens fabrication tolerances. Aplanatic null lenses have been designed and fabricated and are currently being used to test single point diamond machined aspherical Germanium lenses. Interferograms showing a null lens in a stand alone mode and in an asphere test configuration are shown.

Date Published: 11 December 1984
PDF: 7 pages
Proc. SPIE 0508, Production Aspects of Single Point Machined Optics, (11 December 1984); doi: 10.1117/12.944963

Published in SPIE Proceedings Vol. 0508:
Production Aspects of Single Point Machined Optics
Donald P. Brehm, Editor(s)