Dynamic null screens for testing fast aspheric convex surfaces with LCD´s
Author(s): V.I. Moreno-Oliva, M. Campos-García, M. Avendaño-Alejo and R. Díaz-Uribe
Affiliation(s): Universidad Nacional Autónoma de México, Centro de Ciencias Aplicadas y Desarrollo Tecnológico
Topic: 1. Interferometry & Optical Testing Techniques
A method for testing fast aspheric convex surfaces with dynamic null screens using LCD’s is shown. We often for test a fast convex aspheric surface a static cylindrical null screen is used; In the point shifting technique, a rotation or a linear displacement of the screen or the surface has been used. At the present method a flat null screen displayed on a LCD monitor is proposed; the position of the spots on the LCD can be changed in a dynamic way, for doing the point shifting of the image spots. As it was shown before, this reduces the truncation error during the integration procedure improving in this way the sensitivity of the test. The dimensions of the LCD gives the test area on the surface, in order to increase this area, an array of LCD´s is proposed. An important result of this proposal is that the mechanical movement of the screen is reduced or almost eliminated, avoiding the introduction of mechanical errors, such as backlash. The positioning accuracy for the screen spots is related to the LCD spatial resolution. Results of the evaluation of a parabolic convex surface with F/#=0.22 will be shown.