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412 Transactions of SJI.P.E., Vol. XIIJ , No. 38, 1929
the rack method takes about three mmutes longer to produce the same degree of development than the other methods. All the data on rate of development recorded were obtained by the rack and tank method unless otherwise stated.
To interpret correctly the data represented by the time-gamma curves, it is necessary to know the gamma that is used in current practice and the limits in terms of gamma for flat and contrasty development. It was found necessary to determine the degree of development in current use in the commercial film laboratories. Sensitometrically exposed strips of film were sent to nine of the film laboratories in Hollywood, Calif., and developed under normal processing conditions. The gamma values varied from 0.44 to 0.70 with most of them falling in the range from 0.55 to 0.65. H. & D. strips were developed together with a large number of customers' negatives taken outdoors that were developed by judgment in the Eastman laboratory, and these gave an average gamma value of 0.80. This higher gamma value is necessary in the case of commercial negatives taken under average conditions on the eastern part of the United States because the brightness contrast of the objects photographed outdoors is not so great as that prevailing in Hollywood.
The maximum gamma that can be obtained depends upon the nature of the emulsion used, the developer, and the method of development. For Eastman motion picture panchromatic negative film (type 2) with the borax developer and the rack and tank method, the maximum gamma is 1.4. Since the average gamma of studio negatives is around 0.65, it is seen that ample contrast is obtainable with the borax developer.
In the study of developer formulas it is necessary to consider the fog produced as well as the rate of development. The three curves at the bottom of Fig. 2 show the fog values for the borax developer for three different development temperatures.
C. WatJdns Factor
Some workers, who develop negatives by judgment, observe the negative during the early stages of development and determine the time of appearance of the first trace of image. The factor by which this time must be multiplied to give the desired time of development for a normal negative is called the WaMns factor. Tests have been made with various types of negatives in fresh and used fine