Projection engineering (Sept 1929-Nov 1930)

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Projection Engineering, September, 1929 Page 29 Tinted Films for Sound Positives The Problems Revolving Around the Use of Color in Connection With Film Having a Sound Track By Loyd A. Jones* POSITIVE motion picture film on tinted support lias been available for many years. It has been used extensively ; in fact during some periods within the past few years eighty to ninety per cent of the total production has been printed on tinted positive film. There is little doubt that the employment of material which imparts a pleasing and variable color to the screen adds to the beauty of the production, breaks the monotony of looking for lone periods at a plain black and white picture, and softens harsh outlines which otherwise may produce unpleasant impressions. But of much greater importance than these rather incidental esthetic contributions of color is its great potential power to enhance, by either objective or subjective association, the emotional significance of the scene with which it is associated. It must be admitted that the language of color — the more or less precise evaluation of the emotional value of the various hues, tints, and shades — is at present in a very rudimentary stage of evolution. Correlations are in many cases subconsciously felt without being consciously defined. It is entirely possible, and in fact probable, that careful study and experimentation may lead to the development of this language or symbolism into a powerful emotional tool in the hands of the master motion picture dramatist. Recent scientific advances have made possible the reproduction of sound along with the motion picture, the sound record, consisting of a series of photographic images varying in either density or width, being carried on the edge of the positive film band. Although this has ndded enormous possibilities to the dramatic power of the motion picture, it has made it impossible to continue the use of the tinted positive films which have been employed during past years. Tin1 recorded sound is reproduced by the action of light which passes through the record on the positive film and excites a photoelectric cell. The majority of dyes used in making those tinted liases absorb strongly those wavelengths of radiation to which the photoelectric cell is most sensitive. Hence the response of the cell is so reilueed in mag oitude that high amplification of the photoelectric currents Is required to obtain SUffiCienl volume of sound. This high amplification may Increase unduly the inherent cell noises and microphonic disturbances in the amplifier 80 that the reproduced sound is of intolerably poor quality. As a result, the use of tinted film has been entirely discontinued in the production of positives carrying a photographic sound record. There is little doubt that this absence of color from the screen constitutes a serious impairment of the beauty and dramatic power of the screen production. It is desirable, therefore, that a means be found for producing a tinted positive film which, when used in making sound positives, will not interfere with the satisfactory reproduction of the sound record carried thereon. All-over Tints vs. Clear Sound Track This problem can be solved provided coloring materials can be found which, while absorbing a relatively small amount of that radiation to which the photoelectric cell is most sensitive, will produce, by selectively absorbing the radiation to which the eye is sensitive, colors or tints of the desired hue and brilliance. These dyes, or carefully determined combinations of dyes, can be applied to the film base in the usual manner and thus enable the manufacturer to offer a product at no greater cost than the regidar clear base positive film. Another solution of the problem lies in applying the tinting dyes to the film band in such a manner as to leave untinted a narrow strip of proper dimensions and position on the film band. The sound record can then be printed on this uncolored area and the sound will be satisfactorily reproduced without interference of the tinting material. Unfortunately (his method involves a greater cost of manufacture, since the tinting dyes must be applied to the individual 35 mm. strip after the base has been emulsion coaled and cut into DarrOW widths. It is obvious thai technically this represents the most satisfactory solution. This was reCOfi lllllll tiiiiinii Fig. 1. Spectrnl s ensitivity curves for (A) potassium qasfilled photoelectric cell and (B) caesium photoelectric cell. iiiniiiiniiiii nized by us some considerable time ago and applications were made for patents to cover the idea. Methods and machines for accomplishing this have been devised which give very satisfactory results and it is probable that this material will be available in the near future. The first solution suggested, namely, the use of dyes or other coloring materials applied over the entire area of the film and so adjusted spectrophotometrically as to transmit freely the radiation to which the photoelectric cell is sensitive, seemed worth further study, and after a rather lengthy series of experiments a number of satisfactory tints have been obtained. These represent the entire gamut of hue and, in our opinion, are of the most satisfactory depth or color saturation for use in applying color to the motion picture screen. Color Sensitivity of Different Photoelectric Cells In approaching the problem of selecting dyes for this purpose it is necessary, first of all, to determine just what wavelengths of radiation most strongly excite the photoelectric cell with which the tinted material is to be used. It is necessary, therefore, to determine (he spectral sensitively of such cells. Photoelectric cells may be made by using any one of several different materials, such as potassium, caesium, sodium, and other alkali metals. These may be of either the evacuated or the gas-tilled type. The spectral sensitivity depends upon many factors and as a result cells differing enormously in spectral sensitivity are available. To the best of our knowledge, however, there are only two types of cells used extensively in commercial Installations for the photographic reproduction of sound. Qne of these. manufactured by the Western Electric Company and used in the equipment : Presented at thr Man. l!>2a mei of thr Snrirtu of Motion Picture Engineer! • Knrlnl; Research Laboratories. wo too WAVC UJiGTH (rnfi.)