International projectionist (Oct 1931-Sept 1933)

10 INTERNATIONAL PROJECTIONIST November 1931 FIGURE 2 Gray Base Film soluble and washed off in the developer; others contained dyes that were bleached in the developer; while others had to be removed in a separate operation after the plate had been processed. Some of these backings were quite satisfactory for practical use with plates, and came into extensive use in combination with the double-coated emulsions. A great step toward the reduction of halation was made when a thin nitrocellulose film was substituted for the glass plate as a support for the emulsion. Because of the thinness of the film, the halation rings were so reduced in size that they appeared more as a spreading of the blur due to irradiation than as separate rings. Double-Coated Emulsions The use of double-coated emulsions on a film support practically solved the problem of halation with the non-color sensitive emulsions, but this was not quite sufficient with the improved color sensitive materials which have come into use lately. The reason for this is simple. The silver bromide emulsions absorb most of the blue light, but they pass a considerable portion of the yellow and red light. With the non-color sensitive emulsions, this did not matter, because the reflected red and yellow light had little effect on the film. But in the case of the modern panchomatic emulsions, these unabsorbed rays do tend to cause halation. With plates, cut film, or roll film, the dyed backings which are bleached or otherwise removed during processing can be used very satisfactorily, but such removable types of backing are not well adapted for use with motion picture film, because of the danger of offsetting during its passage through the camera, and possible contamination of the developer. With a permanent backing, however, which remains unchanged throughout the processing and handling of the negative there is no danger of chemical troubles in the developer, and if the density, or light absorbing power is properly adjusted, it will give very substantial protection against halation without being too Prints which show clearly the effect of a gray base in reducing halation Clear Base Film dense for printing. Although backings of this type have been proposed from time to time, it is only recently, with the introduction of the "Grayback" supersensitive type of negative films, that they have been widely available to and used by the trade. Gray Base Film, The Eastman Gray Base Supersensitive Panochromatic Negative film is an example of this type. In this film, a neutral gray dye is incorporated in the film support in such a concentration that it absorbs approximately 37 per cent, of the incident light. This does not cause any trouble in printing, but merely requires an increase of one or two steps in the printer exposure. The light which causes halation, on the other hand, must travel diagonally through the film twice, as shown in Figure 1. In comparison with unbacked film, therefore, less than 37 per cent, of 67 per cent, (or under 23 per cent.), of the light producing halation is reflected back into the film. In order to illustrate this effect, the Glass Plate pictures reproduced in Figure 2 were made. The object was a black mask having a series of holes illuminated from the rear. The right-hand picture was made on a plate, and shows the halation rings previously mentioned. The other two pictures were made on supersensitive panchromatic negative film& having the same emulsion, but coated in one case on a clear base and in the other on a gray base. The exposures were equal and the negatives were processed together, receiving identical treatments. The prints show very distinctly the effect of the gray base in reducing the spreading of light around the edges of the image. The two prints reproduced in Figure 3 show how this affects an actual picture. Although it is difficult to reproduce slight differences in quality or detail in the half-tone cut, the illustrations show that a reduction in the halation not only gives cleaner and sharper definition around the highlights, but also apparently increases the contrast in the neighborhood of the highlights. FIGURE 3 y im li a 1 :-' r#«.-A_i5 ? ■ ■ 41 mm so ^B^Mfca f '. ;'• "immiB . tmiaimi , "tr^iism ^Itlfii ■"■' *!lh u^i'*^ urtfT 1 1 MiGIVNEf : 1^^ ■■ ft z», . ■ ■ ■ ■ ■•■;; : ?;.'■ ' *'~r S SI IM^,^«^, ■ .' V l^^l I^Sl .1 _«K> 41 Clear Base Gray Base