Tolerancing surface accuracy of aspheric lenses used for imaging purposes

Tolerancing aspheres and preparing the corresponding drawing indications significantly differ from techniques used at spherical lenses due mainly to surface waviness, an error caused by most asphere fabrication technologies. Standard (ISO) regulations proved to be adequate for several kinds of aspheric lenses (e.g. laser focusing/collimation) made by the traditional diamond turning method, but sometimes are not general enough for recent fabrication techniques (such as CNC polishing of glass aspheres), and today’s more demanding lenses (eyepieces, Fourier objectives, relays etc.). A new, generalized tolerancing technique has been developed to accurately constrain surface waviness, quite independently of fabrication technology, and to provide easy verification of the results. Operation of the method is demonstrated on a Fourier-type objective comprising a glass aspheric lens, by computer simulation and testing of the fabricated prototypes.