TESTING ASPHERIC SURFACES - SIMPLE METHOD WITH A CIRCULAR STOP

As an extension of the knife-edge test, a noninterferometric method fo r inspecting circularly symmetric aspheres is proposed in which the te st surface is illuminated by a spherical wave. When a small circular s top is placed around the curvature center of the best-fitting sphere, only rays characteristic for the deviation from a perfect sphere remai n unobstructed. An image of the tested surface is thereby obtained, sh owing light and dark regions whose boundaries are correlated to the su rface profile, the stop size, and the stop position along the symmetry axis. The experiment has been carried out with a paraboloid. (C) 1998 Optical Society of America.