Centering measurement on aspheres: also double-sided

Abstract

In industry, the use of high-performance, high-precision and, at the same time, lightweight optomechanical imaging systems is becoming increasingly important. The use of aspherical surfaces is playing an increasing role as the number of lenses can be reduced and dimensions and weight can be minimized significantly. In the case of an asphere, on the other hand, decentering is possible as both a displacement and a tilting and this is completely independent of one another. Therefore, the aspherical semi-finished products must be subjected to certain centering rules during the grinding and polishing process and used on the production spindles in an optimized and adjusted manner in order to avoid rejects during production. A subsequent centering process, as is usual with spheres, is then no longer possible. The internal centering error in an asphere-sphere is an immanent offset of the center of curvature of spherical surface to the aspherical axis of the second surface. The new approach of the vignetting Field Stop Technology (V-SPOT) makes it possible to precisely record the local, meridional pitch error in the zone or at the edge of the aspherical surface and, together with the centering deviation of the vertex, to determine the aspherical axis and thus the inner centering error. A short insight into the latest application of centering measurement of double-sided aspheres from only one side using the high depth of field and the large measuring range of the V-SPOT principle is given.