Abstract

The fabrication of mirrors having large departures from a sphere has always been difficult due to the lack of an easy and effective way of monitoring the figure as it is ground into the surface. Grinding in the figure is much faster than polishing so it is a ground surface which must be monitored. This rules out most optical tests. During the fabrication of a 56" off-axis parabola which departs from the best-fit sphere by 125 microns, we developed a simple method of determining the surface profile Using a two-ball spherometer. The method can be applied to any arbitrary circular profile where it is possible to use the spherometer.

© 1980 Optical Society of America