The international photographer (Jan-Dec 1930)

Ten The INTERNATIONAL PHOTOGRAPHER November, 1930 Development and Good Negatives Eastman Official Discusses Relations Between Incorrect Practices and More Common Complaints About Quality By J. I. CRABTREE WHILE there is no question that cinematographers as well as lahoratory men realize the importance of correct development in the making of good negatives it may be of interest to review the relation between incorrect development and some of the more common complaints regarding negative quality in the light of recent researches. The contrast of the negative is determined by the nature of the subject and the quality of the lighting, the nature of the emulsion and developer, and the time and temperature of development. Since most laboratories keep an accurate control of temperature, the usual cause of excessive contrast is an excessive time of development, and, vice versa, a lack of contrast is due to underdevelopment. It is possible to vary the characteristics of the emulsion so that even with prolonged development the contrast of the negative is not excessive, but when photographing scenes in dull weather it is frequently not possible to secure enough contrast with such an emulsion even on prolonged development. An emulsion should be capable of giving a sufficient range of contrast, and the desired contrast should be secured by developing the film to the correct degree. The ability of an emulsion to record shadow detail depends upon its light sensitivity or speed. It is well known if a fast emulsion is developed in a developer containing potassium bromide the resulting negative may only have as much shadow detail as a negative made on a slower emulsion but which was developed in a developer which did not contain bromide. When Developer Is Exhausted As a developer becomes exhausted it accumulates potassium bromide and potassium iodide so that a used developer is incapable of develpoing out as much shadow detail as a fresh developer. Lack of shadow detail in negatives is often a result of developing in an exhausted developer. It has been found by Dundon and Capstaff that by developing an emulsion for a short time in a fresh developer and then continuing development in a partially exhausted developer very little loss in speed results. The effect is clearly shown in Figure 1. Negatives which had received identical exposures were developed in fresh and old developers and pictures printed from these so as to give (a) the best print from the negative developed in the fresh developer, and (b) the best print developed from that in the old developer. These are shown at a, b, c, and d; a and b received equal exposures during printing and likewise c and d. How Detail Is Lost The difference in appearance between a and b and between c and d gives one some idea of the difference in density between the two negatives. A comparison of a and d, which are the best prints obtainable from the four negatives, shows that a decided loss in shadow detail results from using an old developer. The ability of the borax developer to produce fine-grained images is largely due to the high concentration of sodium sulfite (about 10 per cent), which has a decided solvent action on the emulsion grains. If the developer is diluted the solvent action of the sulfite is reduced and therefore its fine-grain producing properties fall off very rapidly. It is, therefore, very important that the developer should not be diluted. If a slower working developer is required the quantity of the other constituents should be reduced, but the concentration of the sulfite should be maintained constant. The process of reducing the size of the emulsion grains by solvent action requires time, so that the longer the time of development required to produce an image of given contrast the greater is the reduction of graininess. In other words, if a negative requires, say, 10 minutes in the usual developer, the graininess may be reduced by reducing the quantity of the developer constituents but maintaining the concentration of the sulfite equal to 10 per cent, so that, say, 20 minutes would be required for the correct degree of development. Increasing Graininess On the other hand graininess of a negative increases with the degree of development or contrast or gamma, so that forced development causes increased graininess. A brilliantly lighted subject requires less development to produce a negative of given density contrast than a flatly lighted one, and in turn it will be less grainy. The difference between the above mentioned factors should be clearly understood, namely (a) graininess increases with the degree of development but (b) for a given degree of development and providing the concentration of the sulfite is maintained constant, graininess decreases as the time of development increases. It is very important, therefore, not to attempt to speed up development of negatives in the borax developer so that development is complete in less than about 10 minutes. Such practices as adding carbonate to speed up development are to be deplored. Fine-grained negatives cannot be made in a hurry — they require time.