American cinematographer (Jan-Dec 1931)

Eastman Super Sensitive Panchromatic Type Two Motion Picture Film by EMERY HUSE and CORDON A. CHAMBERS West Coast Division — Motion Picture Film Department, Eastman Kodak Company ON FEBRUARY 5, 1931, the Eastman Kodak Company announced to the motion picture trade in Hollywood, California, their new Super Sensitive Panchromatic Type Two Motion Picture Negative film. Inasmuch as this film exhibits characteristics not hitherto shown in motion picture negative emulsions, it was considered advisable to present some data pertaining to those characteristics. This article is not presented as a complete technical treatise of the characteristics of the Super Sensitive film, its aim being to call attention briefly and simply to the differences this Super Sensitive film exhibits over the present type of panchromatic films. As the name, Super Sensitive, implies, this 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 extreme speed was desired, either for color photography, filter shots, or trick work, it was customary to especially treat the film with some type of sensitizing bath. This bath caused a general increase in the emulsion speed and particularly increased the red light speed. However, the hypersensitized film had certain disadvantages such as its cost, its lack of keeping qualities, and its propensity to produce fog. With the Super Sensitive Type Two these disadvantages are entirely overcome. The increased speed of the Super Sensitive film has been accomplished during the course of the emulsion manufacture. It is sufficient to say, therefore, that the Super Sensitive film is not a hypersensitized film. Furthermore, the Super Sensitive film exhibits the same keeping qualities and shows identical physical characteristics as those shown by the present panchromatic films. A complete study of any type of film emulsion is best accomplished by making both sensitometric and practical camera tests. This article will not deal in any detail with camera tests but will consider in some detail the sensitometric characteristics of the Super Sensitive emulsion as compared with the present type of panchromatic film. The point of major importance in the consideration of the Super Sensitive film pertains to its greatly increased speed. The data obtained sensitometrically 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 consideration in studying the need of the Super Sensitive film necessitates a study of the quality of the light sources to which this film is exposed. For that purpose sensitometric tests have been made to daylight and to tungsten. Inasmuch as the mode of testing an emulsion to any light source is practically identical we shall for the sake of brevity and clarity consider only the curves obtained by exposure to tungsten. Figure 1 shows the sensitivity curve of the present and Super Sensitive type of film for tungsten exposures developed for a fixed time, nine minutes in a standard borax developer. It will be observed that the Super Sensitive curve lies above the curve for the present type of film and the separation of these curves gives an indication of the speed difference existing between the two films. In making a numerical estimate of the speed we do not consider the actual density values produced for a given exposure. The customary method is to deduce speed from the exposure value obtained at the point where the straight line portions of these sensitivity curves, extended, intersect the exposure axis. Speed, is usually defined by the following formula: 1 — x C = Speed, i where i, the inertia, is the exposure value of the intersection point and C is an arbitrarily chosen constant. For the curves shown in Figure 1 we find that the speed of the Super Sensitive film, as represented by curve No. 2, is three times Exposure : Tungsten oo as oa as tz is ti v* ti Fig. 1 that for the present type films. Identical tests made to daylight show that the Super Sensitive film is twice the speed of the present type. With reference to Figure 1 attention should be called to the marked difference in the low exposure region, that is in the toe of the H and D curve. In this region the Super Sensitive film definitely differentiates between exposures of very low intensities. Particular reference is made to the exposure region to the left of the relative log exposure value of 0.3. The cause for the difference in relative speeds between the two types of films to tungsten and to daylight, or to any other source, is entirely dependent upon the color distribution of light from the source and its effect upon the color sensitivity of the emulsion. It is generally known that tungsten, for example, contains a greater proportion of red light than does daylight, and the difference in speed of the two films indicates that the Super Sensitive film must possess greater sensitivity to red light than the present type of film. It is mainly for this reason that the tungsten speed of the Super Sensitive when compared to the present type of film is greater than for a similar comparison to daylight. The difference in color sensitivity of the two types of films is shown in Figure 2. This figure shows prints of spectrograms of the two types of film when exposed to tungsten. Speed comparisons should not be drawn from these prints as the 9