Abstract
Within the past ten years a variety of CNC manufacturers for aspherical surfaces have been established. The field of applications they are working for are very different. The way CNC manufacturers measure surfaces as well as the way they characterize the surface form deviation differs even more. Furthermore, there are a lot of customers being interested in using aspherical surfaces in their applications. In fact, aspherical lenses are not established as standard optical elements yet which is due to the fact that many users are not familiar with the implications of the use of aspherical surfaces with respect to the tolerancing of the optical system. Only few know how to specify an asphere, moreover, they differ about how to do that. The paper will give an insight in what is possible in aspherical manufacturing in terms of accuracy, efficiency, number of pieces per design and surface forms. An important issue is the development of deviation of form and slope in connection to prepolishing and correction polishing. Based on experiences of the manufacture of more than 500 different aspherical designs with diameters ranging from 3 - 200 mm, the paper is going to give an insight into production practices. Finally, there will be a general overview on what could be done and what needs to be done in order to unify the different ways of tolerancing of aspherical surfaces.