|
An optical surface is generated with a very high accuracy with regard to its macro and micro geometry so that rays falling onto this surface are deflected with image-forming quality. Materials for optical elements must have high transmission or reflectivity in a given spectral range. These requirements are met by some crystals, optical glasses and plastics and some metals. There are different methods for generating optical surfaces: - precision moulding and pressing - turning or flycutting - grinding, lapping and polishing Moulding and pressing are applied to optical plastics and to glasses. Normally elements produced in this way fulfil only low requirements with regard to surface quality and homogeneity. However precision moulding of glass lenses with remarkable high quality could be achieved recently. On soft materials optical surfaces can be generated by precision diamond turning or flycutting. These techniques require high-sophisticated design of computer controlled machines. Optical glasses cannot be machined by single point diamond turning because of the hardness and brittleness. For special applications the problems are solved by turning the glass at an elevated temperature. Under certain conditions several types of optical glasses can be turned to a transparent finish. Also in the classical methods for generating optical surfaces, i.e. gringing and polishing, changes can be observed at present. This relates to rigidity and precision in machine construction, to materials and geometry of grinding and polishing tools and to polishing agents.
|
