The Cine Technician (1935-1937)

Aug'. -Oct., 1936 The Journal of the Association of Cine-Tech)iicians 57 sion in general use in the motion picture field. It is today almost exclusively used for the production of projection background plates but other uses are being found for this film because if its very fine grained characteristic. In all the foregoing paragraphs there has been presented a miniature chronological history of the factors which have lent themselves to the achievements of photographic work which are possible to-day in the motion picture field. While it is the purpose of this paper to discuss particularly the current Eastman motion picture negative emulsions, such a discussion could not be given satisfactorily without devoting considerable time to a discussion of accompanying developments along other hues. Since it is felt that the historical side of this problem has been established, it is now possible to proceed with a discussion of the photographic emulsions themselves and the differences which exist between them. The original panchromatic motion picture negative film as introduced in 1927 and the later Type II film, although of more recent origin, are more completely removed from the motion picture field of photography than the old type orthochromatic negative, since this latter film is still manufactured for certain laboratory purposes. It is interesting to note that for such purposes this film is rapidly becoming obsolete. The three Eastman motion picture negative films now available are Super-Sensitive, Super X, and Background. A detailed graphical and quantitative comparison of the characteristics of these three emulsions may be had at a glance by a comparison of Figures 1, 2, and 3. It will be observed that the color sensitivity difference between these emulsions is slight. The Super-Sensitive and Background negatives are essentially the same in this respect. The Super X Negative differs slightly in that its red sensitivity is somewhat reduced. This fact can be readily determined by a comparison of the filter factors of the 23A (red) filter. The filter factor of this filter for Super X Negative is 4, while for the other two films it is 3. Since the filter factor is a multiplying factor for exposure, the larger that factor the lower the sensitivity. The data on these three emulsions were obtained under identical conditions of testing. Exposures and subsequent development were simultaneously made. These emulsions may be classified in the order Super X, Super-Sensitive, and Background Negative in terms of descending speed, while from a contrast standpoint the emulsions would range in the same order for ascending contrast characteristics. It will be seen, furthermore, that the characteristics of these three emulsions are tabulated for different values of gamma. This point needs some explanation. When Super-Sensitive Negative was in general use the average degree of development given it in the motion picture laboratories was represented by a gamma of approximately 0'65. Gamma is that characteristic of the film which indicates the degree of development. With the introduction of Super X Negative and its generally lower contrast characteristic it was found desirable to raise the average gamma to 0*70, it being determined by practical test that the emulsion quaUty of this negative was greatly enhanced at this slightly higher value. This change in average gamma from 0"65 to 0*70 represents an increase of only approximately 8°;,. Since the Background Negative is inherently one of high contrast and since one of the purpo.ses of the Background Negative is to produce a somewhat more contrasty result, it was found that an average gamma of'0-75 was desirable for this material. It should be well understood that these values of gamma are approximations since they represent the average extent of development of these films in practice. Departures plus or minus from these average values are naturally at the discretion of the individual user. The times of development to produce these average gamma values for each type of negative progress from the Background Negative, for which a short time of development is necessary, through the Super-Sensitive to the Super X, which requires the longest time. It was stated in a previous paragraph that Super X Negative is used in far greater quantities than the Super-Sensitive Negative. While this statement is true, it should be stated here that SuperSensitive Negative film is still available for those users desiring this type of emulsion. However, indications point to the fact that before long Super-Sensitive Negative will be completely supplanted by Super X Negative. Before leaving this subject it might be well to give some consideration to the various characteristics of emulsions and a bearing each has upon that intangible factor, photographic quality. There are many proponents to the idea that speed in a negative emulsion overshadows all other characteristics and that high speed is the most essential quality of a high grade negative emulsion. This is not true. Speed has a definite role to play because an emulsion must have sufficient sensitivity to record adequately low light intensities ; otherwise a burden is thrown upon the cameraman in the lighting of his sets. Speed, therefore, while important, is by no means the major factor to be considered in a negative emulsion from the standpoint of obtaining photographic quality. When one stops to consider that the negative emulsions of four years ago were approximately one-quarter the speed of the current emulsions, one wonders now that pictures could have been made with those older type films. In the light of our present emulsion knowledge, Super X Negative film represents the highest speed of present comrr.ercial motion picture negati\"e emulsions consistent with excellent photographic quality. It is quite possible to make faster emulsions, but not without a sacrifice of some of the other fa\'ourable factors. Photographic quality is a condition brought about by the combination of several elements, of which emulsion speed is but one. Contrast and graininess characteristics are the other factors ol major importance. It is generally well known among photographers that high speed emulsions usually show low contrast and large grain size. In a slower emulsion, high contrast and fine grain align themselves together. This is a very important point and should be given full consideration. It is quite possible that as emulsion manufacturing knowledge ad\'ances these facts, now considered laws might be overcome, but in the manufacture of gelatino-silver bromide emulsions, speed, low contrast, and large grain size usually go hand in hand. The one exception to this is the current Super X Negative. This emulsion shows a finer grain characteristic than some of its slower predecessors, but it is extremely doubtful that a faster emulsion than Super X Negative could be manufactured without showing a greater tendency toward graininess. While it is admitted that great .speed would allow for more natural set lighting, it does not follow that the quahty of the resulting pictures would be better unless the negative emulsion had contrast and graininess factors comparable to those in the current type negative emulsion. It should again be emphasized that statements relative to the possibility of manufacturing various types of emulsions depend entirely upon current knowledge. It is quite probable that as the result of more extensive research, em [Contuiitcd uii page 59)