Projection engineering (Jan-Dec 1931)

DECEMBER, 1931 Page 21 Eastman supersensitive motion picture negative film f By Emery Huse and Gordon A. Chambers* AS the name "supersensitive" implies, the new Eastman supersensitive panchromatic type 2 emulsion is extremely fast, but because of its name this new film must in no way be confused with a hypersensitized film. In the past when an emulsion of very high speed was desired for color photography, filter shots, or trick work, it was customary to especially treat the film in some kind of sensitizing bath. This bath caused a general increase of speed, and particularly increased the speed of its reaction toward red light. However, the sensitized film had certain disadvantages, such as its cost, its lack of keeping-qualities, and its propensity to produce fog. In the supersensitive type of emulsion these disadvantages are entirely overcome. The increased speed of the new film is obtained during the course of manufacture. It is sufficient to say, therefore, that the supersensitive film is not a hypersensitized film. Furthermore, it exhibits the same keeping-qualities, and shows identical physical characteristics to those shown by the present panchromatic films. A complete study of any type of film emulsion is best accomplished by mak ^ Presented at the S. M. P. E. Spring, 1931, meeting at Hollywood, Calif. *West Coast Division, Motion Picture Film Department , Eastman Kodak Company. ing both sensitometric and practical camera tests. This paper will not deal in any way with the camera tests, but will consider in some detail the sensitometric characteristics of the new emulsion as compared with the present pan-, chromatic emulsion. The point of major importance in considering the new film is its greatly increased speed. The data obtained by sensitometric measurements can be, and have been, checked by camera exposures. Sensitometry involves a study of known values of exposure as related to the amount of silver (density) which these exposures produce upon the film after development. The standard sensitometric curve is therefore one in which is shown the relationship between exposure (expressed logarithmically) and the densities produced. It is from curves of this type that the sensitometric characteristics of the films under investigation have been studied. Another important point that must be considered is in relation to the quality of the light to which the film is exposed. For this reason sensitometric tests have been made exposing the film to daylight and to light emitted by a tungsten source. Inasmuch as the method of testing an emulsion when exposed to any kind of source of light is practically identical, we shall, for the sake of simplicity, consider only curves obtained The advantages which the new supersensitive film has over the present type of film are described, and comparative photographic characteristics of the two types of film are presented. In addition, the paper includes a brief discussion of the particular features involved in the use of the faster film, such as the difference in color sensitivity of the two types, and relative contrast, and the rendering of details in shadows and soft highlights. Users of the new film are cautioned against the danger of processing it when using the present safe lights, on account of the greater speed of the emulsion. The paper concludes with a description of the gray base which has been provided, mainly for the purpose of avoiding halation. on exposing the film to the light of a tungsten source. Fig. 1 shows the sensitivity curves of the present and the supersensitive types of film, exposed to a tungsten source and developed for a fixed time of nine minutes in a standard borax developer. It will be observed that the curve for the supersensitive film lies above the curve for the present type of film, and that the separation between these curves is a measure of the difference of speed of the two films. In making a numerical estimate of the speed we do not consider the actual densities produced by given exposures ; it is customary to deduce the speed from the exposure indicated by the point where the linear portions of the sensitivity curves produced intersect the exposure axis. Speed is usually defined by the following formula : 1 — XC= speed i in which i, the inertia, is the exposure indicated by the point of intersection and C is an arbitrary constant. For the curves shown in Fig. 1 we find that 00 0.3 06 09 Fig. 1. Sensitivity curves of present film and supersensitive film. the speed of the supersensitive film, as represented by curve No. 2, is three times that of the present type of film. Identical tests made with daylight exposures show that the supersensitive film has twice the speed of the present type. Attention should be called to the marked difference between the curves in the region of low exposure, that is. in the "toe" of the H & D curve. In this region the supersensitive film definitely differentiates between exposures of very low intensities. Particular reference is made to exposures less than that indicated by relative log E = 0.3. The cause of the difference between the speeds of the two types of film when exposed to a tungsten source and to daylight, or to any other source, is entirely dependent upon the color distribution of the light emitted by the source, and its effect upon the emulsion as determined by the color sensitivity. It is generally known that tungsten sources, for example, radiate a greater proportion of red light than is found in daylight, and the difference between the speeds of the two films indicates that the supersensitive film must be more sensitive to red light than the present