Chromatic distortion represents a limit parameter for many optical systems. For telescope objectives low chromatic aberration is especially important. The choice of appropriate materials is therefore crucial for the production of optical elements.
The S-FPL-53 glass produced by Ohara Corporation is a readily available material with low dispersion. Its high Abbe number indicates low achromatism, therefore it is used in all the above-mentioned designs to achieve good correction. On the other hand, this fluorite glass is quite soft and has a high thermal expansion coefficient, so it is really difficult to polish.
In this paper possible solutions to problems related to polishing aspherical lenses applying CNC technology and to polishing spherical lenses applying classical technology are discussed. By combining various conditions it is possible to achieve required roughness and shape of the lens surface.