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Oct., 1931] SUPER SENSITIVE NEGATIVE FILM 565
commonly referred to as time-gamma curves, show the rate at which the gamma increases with the time of development. The rate of increase of the gamma of the supersensitive film is appreciably less than that of the present type of film, as inspection of the curves of Fig. 4 will show. This means that there is much less chance of overdeveloping or under-developing the film during processing. Errors of the order of 25 per cent in the time of development will show much less effect on the supersensitive film than on the present film. In other words, the new film provides for a much greater "development latitude."
One important caution must be mentioned; due to the great sensitivity of the new emulsion, the film cannot be successfully handled unless the light emanating from the present safelights is considerably reduced. It would be best to handle the film in total darkness; no doubt this will be done, inasmuch as many camera loading rooms and laboratories where negative film is processed in machines are kept quite dark, if not totally so. It is felt, therefore, that this requirement will not cause any great hardship; however, this word of caution is considered necessary on account of the greatly increased speed of the new film with regard to both white and colored light.
GRAY BASE FILM
Since the introduction of the supersensitive negative another decided improvement has been made which will generally enhance photographic quality. The emulsion is now coated on a gray base, mainly for the purpose of preventing halation. The gray base was introduced to the motion picture industry in May, 1931.
Halation has always been a source of trouble for photographers. The halation which appears as a glow encircling the highlights of the picture is due to the reflection by the rear surface of the film base of the light which has passed through the emulsion and the support, so that it becomes incident. upon the sensitive surface a second time, this time from the rear. In the case of glass plates where the thickness of the emulsion support is appreciable, halation is very serious, while in the case of the thin film base the effect is so reduced that in ordinary photography it is negligible. Indeed, one of the advantages that has always been claimed for film, as compared with plates, is the great freedom from halation which the former provides.
The importance of halation, however, is a relative matter. A spreading of light which is utterly negligible in an 8 X 10 picture