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1945 Theatre Catalog, 4th Edition, Page 327 (303)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 327
Page 327

1945 Theatre Catalog, 4th Edition, Page 327

more the exception than the rule. White light brings with it minor complications. Whereas a transmission film, which will flatly refuse to reflect light of one particular wavelength, can be made, such a feat is impossible for the wide range of wavelengths in white light. At least, it is true with the type of films presently under discussion.

The reason for this lies principally in the inability of a film to fulfill the quarter - wavelength requirement for more than a single wavelength. The optical thickness of a given transmission film is correct for only one position in the spectrum, and it is for this wavelength that the reflectance of the film surface is a minimum. Neighboring wavelengths show a progressively increasing redectance as the departure from the optimum becomes greater. This preferential reflectance from a filmed surface tints the reflected images formed by it, and in this sense the film filooksll colored. The particular f(tint" is indicative of the filmls thickness.

The phenomenon is easily understood if the process of reflection is visualized as the film builds up. When the film is thin, it shows a minimum reflection in the violet, so white light reflected from this film is deficient in violet and, consequently, appears brown. As the film thickness increases, the position of the minimum reflectance wanders toward the longer wavelengths. When it has arrived midway in the green, the reflected light becomes a magenta, and when the minimum is in the red end of the spectrum, the hlm appears to be blue. These color changes are so marked that color gauges have been devised for determining the thickness of the films. The usual commercial practice is to control the film thickness visually with a small hand-held fluorescent light. At the Radio Corporation of America, however, an electronic control has been devised.

However, this tinting effect which is so apparent in refiected beams, is so weak in transmitted and projeccted beams that it is, for the ordinary eyes, not observable, either in black-and-white or in color photography. Indeed, the first coated Super Cinephor lenses made for motion-picture projection by Bausch and Lomb in 1939 were used on all showings of the Technicolor production ffGone with the Wind." The lenses are coated to give maximum transmission in the greens; this mid-point in the visible spectrumacoincident with the region to which the eye is most sensitiVHhaving been determined as the place of most satisfactory results for motion-picture projection, including color films.


A few words should be said about the future applications of transmission films. Low reflection films were developed and perfected to their present state in specific response to war need, but their peacetime applications are so numerous that they will probably become a permanent feature of our industrial set-up.

Undoubtedly all camera and projection lenses will be coated to improve the quality of natural-color photography as well as those of the ordinary black-and-white.


ALL THE GREMLINS OF OPTICAL SCIENCE 90 to work when a cameraman shoots into the sun - a feat which, of course, is not done if a final picture is desired. And in this photograph is seen what happens. Reflections, flare, ghosts, and all the others become apparent in the finished picture. This photograph was taken with a Bausch and Lamb, 88-mm. wide-angle, uncoatad lens. Compare this with the similar picture below. (B&L photo.)

Certainly eyeglasses, watch crystals, clock faces, instrument cover glasses, microscopes, field glasses and opera glasses, and the like will be among the first of the other articles to be coated to remove annoying reflections.

And, finally, methods may be invented to remove reflections from large surfaces, such as windows in store fronts, automobiles, railroad cars, show cases, display frames, and homes.

Approximately 95 per cent of all the

optical glass manufactured in the war years was used by the Armed Services. Hence, the most recently developed applications of transmission films have been connected with military instruments. It is hoped, however, that this short discussion has demonstrated that, out of the holocaust of misery and chaos that is war, there will emerge developments which will make life more pleasant when peace again settles upon the earth.

THE "IMPOSSIBLE" IS ACHIEVED on the same scene, by using Bolcoteasurfaced lens of identical design. Other details-light, exposure condition, and the like-were the same. While some imperfections occur-the most perfectly coated lens, of course, will not eliminate 100 per cent of the reflections-the improvement is remarkable. What happens with a still-camera lens can be made to obtain cinematographically. (Bausch and lamb photo.)
1945 Theatre Catalog, 4th Edition, Page 327