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96 IV. MAKING 16-MM ORIGINALS
measurements in film laboratories are made with an Eastman densitometer or equivalent.
Standardization of Emulsion Speed
No two emulsion lots of even the same kind of film are of the same speed. To be effective, a control method for density must take this factor into account. When film emulsions are manufactured, it is not possible to predict with absolute accuracy just what the speed and other sensitometric characteristics of a particular mix are going to be. For this reason it is common practice among sound recordists to discuss sensitometric characteristics of films in terms of their specific applications. Thus, in the case of EK 5372, for example, the speed of a particular lot of film is said to be so many milliamperes faster or slower than the reference emulsion lot.
Check the materials on hand and identify them properly. In the average case, this means that a stock of 6 recording lamps is on hand together with the month's supply of the new emulsion lot number, as well as at least one full unopened can of the emulsion lot number being retired. Load the recording machine magazine with this roll of the old emulsion lot number of film. Make a recording following the procedure outline in "Recording the Exposure Test/' steps (1) and (2). At the conclusion of this recording turn off the power supply. Remove the exposed film from the magazine and place it in the original container. Complete the log sheet. Make a note on the log sheet : ' ' This is an emulsion test. Please read the densities of the exposures indicated and note these beside the exposures. Develop (for direct positive — 3 minutes). Return the original log sheet ; retain the carbon copy for the laboratory file.', Remove the unexposed film from the magazine; seal it in a can in the usual manner ; and identify the can with the proper emulsion lot number and other identification so that the test may be repeated at a later date if necessary.
Do the same for a test roll of the new emulsion lot. When storing the unused part of the test roll, make certain that the identification is correct and complete. Send the films to the laboratory.
Upon return of the completed lop: sheets from the laboratory, plot a curve for each of the two lot numbers of film in the same manner as for two new lamps. The difference between the lamp currents at density 1.50 is the Direct Positive Film Difference Current. If the new film requires more current than the older one, enter in the log book: "Add film