International projectionist (Jan 1959-Dec 1960)

CHROMATIC ^-WHITE LIGHT ABERRATION ^ ^FOCUS OF APPARENT^ \ FOCUS OF' RED LIGHT FOCUS OF \ BLUE LIGHT red LIGHT APPARENT FOCUS OF BLUE LIGHT FIGURE 1. Example of simple negative and positive lens Devious Ways of Light and Lenses By H. E. ROSENBERGER Scientific Bureau, Bausch & Lomb Optical Company Question: Certain statements in the article "Index of Refraction" which I reread in IP recently intrigue me, notably that stating "such a medium as glass must have one refractive index for each wavelength of light." Now, then, since red is a longer wavelength and travels faster through glass than does blue light, how is it that when we project color pictures we get a comparable color conformation on the screen as has the original print? Bertrand S. Webster Appended is a brief but inclusive explanation of how this basic problem was overcome through intensive research and applied science. BECAUSE the index of refraction of glass varies with the wavelength (color) of light, a simple lens bends the different colors by different amounts, as is shown by the simple positive and negative lens illustrated in Fig. 1. The distance between the red and blue foci is called the "longitudinal chromatic aberration" of the lens. This distance depends, in part, upon the power of the particular lens and, in part, upon the so-called "dispersion" of the glass used in the lenses. The optical industry has developed hundreds of different kinds of optical glasses, some having a very high dispersion, and some having a very low dispersion; while others fall between these two extremes. Unfortunately, it has not been possible to produce glasses with zero dispersion. Negative vs. Positive . . . The optical designer, however, has found ways to overcome this difficulty. It will be observed in Fig. 1 that the positive lens brings the red light too far to the right of the blue; while the negative lens brings the red light too far to the left of the blue. What happens then? Just this: the lens designer, taking advantage of these physical facts, proceeds in time-honored fashion to play the positive against the negative, as follows: He selects such combinations of lenses which, by combining a positive lens element made from one kind of glass with a less powerful negative lens element made from another kind of glass, results in a lens having a net positive power — and at the same time insures that the chromatic aberration of the negative element cancels out exactly the chromatic aberration of the positive elements (Fig. 2). Any other questions? — ED. ACHROMATIC LENS WHITE LIGHT FIGURE 2 Versatility of Film Cited by Kodak Executive Advantages of motion picture film in the production and presentation of TV programs were discussed by Ed Stifle, of Eastman Kodak, before a recent meeting of the Radio & TV Executives Workshop. Stifle spoke primarily of the capabilities of color film, its characteristics and flexibility for production, and its equipment. He pointed out that a major advantage of motion-picture equipment is its portability and availability. Film scenes can be shot anywhere in the world, in studios or on location, in contrast with the limitations of bulky TV cameras, coaxial cables, and auxiliary equipment. Film camera equipment provides good color-matching between scenes, he added, and it also permits animation, along with "live" action, if desired. Flexibility a Primary Concern The production flexibility of film is outstanding, Stifle emphasized. A producer can shoot scenes in any sequence, backward or forward, and can speed production and trim costs by using multiple camera crews. He can "freeze" a single frame, stop or reverse action, or introduce optical effects for greater realism and impact, if desired. Stifle noted, too, the great benefit in having an existing library of film footage available on call. Other advantages of film, such as direct visual inspection of the image and easy editing, plus simple splicing at any frame, are sometimes so much taken for granted that their true value to swift, quality production lias perhaps been underestimated. Stifle said. Definition Gives "Tone" Value Because of the universality of projection equipment, moreover, film can be presented readily over any TV station. Cited was the wide scope of use provided by film for such presentations as sponsor and station previews, regular telecasting, theatre screenings, and program syndication. Film characteristics have been developed and improved so that a wide choice in types of color and black-andwhite films is now available. Today's films have adequate sensitivity and provide excellent definition and tone reproduction, said Stifle. Research and engineering have provided some 16 different films for different kinds of color, and laboratory facilities have expanded so that color is versatile and readily available on a service basis similar to black-and-white. Significantly, a public relations representative for the tape industry admitted that the full potentialities of the medium could not be realized for at least another three years. INTERNATIONAL PROJECTIONIST JANUARY 1959 1]