OF ALL the technical advances to come out of the recent war, probably the most significant optically is the coating of lenses with reflection-reducing films. Now that coating has been made available to members of the profession, an appraisal of it is in order, for at present it has both limitations and important uses.
This development had its beginning as far back as 1892, when H. Dennis Taylor, a lens designer of England, observed that the iridescent tarnish which appeared on certain old camera lenses did not reduce the light they transmitted, but increased it instead. The thin film1 on these optical surfaces reduced reflections and increased the transmitted light by the amount of reduction of the reflections.
The physical conditions which produce zero reflection of monochromatic light are two. The film must equal in optical thickness one quarter of a wavelength of the incident light, and the refractive