ABSTRACT
As has already been mentioned in Chapter 1, antireflection coatings were the principal objective of much of the early work in thin-film optics. Of all the possible applications, antireflection coatings have had the greatest impact on technical optics, and even today, in sheer volume of production, they still exceed all other types of coating. In some applications, antireflection coatings are simply required for the reduction of surface reflection. In others, not only must the surface reflection be reduced, but the transmittance must also be increased. The crown glass elements in a compound lens have a transmittance of only 96% per untreated surface, while the flint components can have a surface transmittance of as low as 90%. The net transmittance of even a modest number of untreated elements in series can therefore be quite low. Additionally, part of the light reflected at the various surfaces eventually reaches the focal plane, where it appears as ghosts or as a veiling glare, thus reducing the contrast of the images. This is especially true of the zoom lenses used in television or photography, where 20 or more elements may be included and which would be completely unusable without antireflection coatings.
