The experienced lens designer is well aware of the potential advantages aspherics can afford. Within the last few years,
machines specifically designed for the CNC machining and polishing of glass aspheres have become commercially
available through several manufacturers. This has brought down manufacturing cost to the point that designs
incorporating aspheres can be used to reduce system cost compared to all spherical designs. (That is aspheres are no
longer used just to save space and weight at the expense of cost.) Not all aspheres are equally manufacturable, however.
Arbitrary choices at the beginning of a design can have major impact on manufacturing cost and limit final "as built"
performance. This paper considers factors in designing ground and polished (as opposed to molded) glass aspheres
which may not be obvious to even the experienced lens designer accustomed to using spherical surfaces or who has dealt
with diamond turned aspheres. Factors considered include the surface shape, how the shape is specified, how the surface
is to be tested and how it is toleranced. Emphasis will be placed on medium priced components where practical considerations are important.