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748 Transactions of S.M.P.E., Vol XI, No. 82, 1927
before which the film is placed. The width of the aperture and the relative times of exposures can be adjusted to match the printer.
President Cook: Is the sensitometer described several years ago by one of the research laboratory men of the Kodak Company available commercially?
Mr. Crabtree: No, it is not available commercially. It was simply an experimental model. Mr. Ives and I have described a semi-automatic sensitometer which any carpenter with a little electrical knowledge can construct. The great difficulty in the adoption of this type of sensitometer has been the preparation of the tablet. The only object of giving this paper was to explain how a laboratory man could prepare one himself. It is a very difficult problem to make a tablet to match a machine remote from Rochester . It is necessary to have access to the machine to get a tablet to match it.
Mr. R. C. Hubbard: With regard to the Cinex machine, you do get a slightly different quality due to the focal plane shutter used in this type of sensitometer than in the type just described.
President Cook: It would seem that a graduated sensitometer tablet of this sort, as described here and as described previously in the machine that you used, would be better adapted for a printing machine using an electrical light control than a diaphragmatic control.
Mr. Crabtree: I don't think it would make the slightest difference provided the sensitometer was adjusted to the printer.
President Cook: The element of the actinic value of the light under rheostatic control complicates the matter.
Mr. Hubbard: There is a perceptible difference in printing lights; that is, control with the rheostat changes the color of the light, and emulsions are sensitive to variations in color. You would find that this would affect the quality of the print ; that has been my experience.
President Cook: That was what I was trying to bring out, but Mr. Crabtree says that would not have any effect.
Mr. Crabtree: With regard to the effect of the change in color of the light of the printer lamp with change of voltage, it is, of course, well known that the contrast of an image is affected by the wave-length of the light used to produce it. In the case of Eastman DupHcating Film, we control contrast by the use of a violet filter which reduces contrast. However, this contrast variation is only