American cinematographer (Oct 1933)

212 American Cinematographer • October 1933 POSITIVE CONTROL DATA F ROM the standpoint of positive control the procedure followed is very similar to that described for nega- tive film. The final positive print contains both pic- ture and sound track records. It is important from the standpoint of the sound that positive gammas be specified and maintained. For that purpose rigid control is applied to positive film development so that the predetermined positive gamma may be maintained consistent throughout. This is particularly true in release print development. At another major -studio laboratory control data have been obtained for a period of one day. This laboratory sub- mitted all of their data on positive control for March 26, 1933. This consisted of each individual sensitometric curve for every machine in operation during that day at intervals of about one hour. During the day’s work there were five developing machines in operation, each machine having in its system the same chemical formula. At this laboratory a positive control gamma of 2.00 is desired. By preliminary sensitometric tests, which consist of the development of Type lib positive sensitometer exposures on the positive film emulsion which is in use, gamma determinations are made before any production work goes through. With these data it is possible to determine the time of development to give this desired gamma value. This time is controlled by the machine speed. In Figure 7 is shown a typical positive H and D curve giving an approximate gamma of 2.00 as obtained at this laboratory in one of the machines on the day in question. From this graph the general density range covered by the sensitometric strip, as well as the general shape of the curve, is readily seen. Once the time is de- termined to give this desired gamma, production starts and hourly thereafter a pair of sensitometric exposures are sent through. Each strip is then read for density and plotted. Upon the completion of the work a final curve is obtained showing gamma plotted against the time interval of de- velopment. Naturally there are some tests which show values greater or less than the desired value. Certain tolerances are, of course, allowed, usually a plus or minus .05 deviation from the normal. In the data which are presented in Figure 8 the actual variations are readily ob- servable for each machine. The work during this day was not representative either of a good or a bad day but did show a perfectly average set of conditions. For any given machine for example machine No. 8, there is only a .06 maximum variation between the highest and lowest gamma strips. If all of these values of gamma were averaged a numerical gamma of 1.995 would be obtained. The maximum de- viation, considering all machines, was only .07. In the event that any general trend is shown by successive tests, then slight alterations are made in the actual time of development to compensate for that trend. It is the func- tion of the foreman in charge of the positive developing machines to maintain the desired gamma of 2.00. From the data presented from this laboratory it can be seen that the results are excellent. At this point it should be cited that similar conditions prevail in all of the laboratories in the Hollywood area and particularly those doing release printing. However, the purpose of this paper is to cite the sensitometric routine in vogue and to show the results obtained and it is fair to state that the results shown from this laboratory on their positive film control is indicative of the type of work obtained by all of the laboratories in Hollywood. As was the case with negative developer formu- las, a similar condition of difference exists from the stand- point of positive formulas. To complete this section on positive film control the tabulation of an average positive formula is considered necessary. Table 5 gives such a formula. *■—Paper delivered by Mr. Huse at April, 1933, S.M.P.E. Convention. Sensitometric TABLE 5 Picture Positive Formula Elon 1 2 ozs. Sodium Sulphite 40 lb. 8 ozs. Hydroquinone 4 lb. 14 ozs. Sodium carbonate 26 lbs. Potassium metabisulphite 1 lb. 7 ozs. Potassium bromide 10 ozs. Potassium iodide 178 grains Water to 120 gallons SOUND CONTROL DATA A complete discussion of the sensitometric control for sound film development would be extremely voluminous. In the discussion of this subject in this paper no attempt will be made to give actual data from any individual studio. The control methods are similar to those described for posi- tive and negative film but are much more detailed in many respects. There are at the present time two major sound recording methods in vogue, the R. C. A. and the Western Electric systems. A brief discussion is necessary for each of these two methods. They differ appreciably and should be dis- cussed separately. The R. C. A. system makes use of a variable area sound track, while the track of the Western Electric system is of the variable density type. VARIABLE AREA The particulars regarding this system of sound recording are very well known and this paper will give only the neces- sary details to describe the sensitometric requirements which are submitted to their licensees by the R. C. A. Victor Co. They are quite simple and are readily maintained in the processing laboratory. The specification laid down by R. C. A. Victor engineers for negative gamma is that the negative sound track should be developed to give a control gamma of from 2.00 to 2.20. The unmodulated track density, and in this instance refer- ence is made to the symmetrical track, should fall within the density range of 1.40 to 1.50. The sensitometric setup necessary to follow these specifications requires that the laboratory determine the time of development on the film being used for the recording to give a gamma within the limits just prescribed. It is then necessary for the recording unit to provide an exposure which will give a density upon development within the density limits cited above. R. C. A. Victor recommends for positive control gammas between 2.00 and 2.20, similar to the negative, while the positive track densities should be from .15 to .20 less than the negative density. For example, if the negative unmodulated track density at the proper gamma is 1.45, then the posi- tive track density should be within the limits of 1.25 to 1.30. Naturally, during the course of processing, solution control must be maintained, and this is accomplished in a manner very similar to that previously described under positive film Once the set of sensitometric conditions are determined, both from the exposure and development stand- point, then it is the function of the laboratory to main- tain those conditions in their developing procedure. The developer normally used for this type of work is the regular picture positive formula, an example of which was cited under the heading of positive film.