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Ten
AMERICAN CINEMATOGRAPHER
June, 192C
Effect of Desensitixers in Deuelopment
Part Two of Investigations on Photographic Developers Is Released
Bij m. L. Dundon and J. I. Crabtree
Of the Eastman Research Laboratory.
Paper Was Read at Spring Meeting of Society of Motion Picture Engineers
SERIES A
SERIES 3 MO EFFECT
SERIES 2.
SERIES 1 SERIES 0
SERIES 00
Figure Tivo — Relative photographic effect of Wratten safelights on Panchromatic film.
I. Introduction.
The inspection of film during development is often desirable even though the time and temperature method can be used to produce negatives of a definite development contrast or gamma. Especially in the case of motion picture film, where only one positive material is used for printing all scenes, the production of negatives of fixed density contrast is desirable. In order to obtain this result the time of development must be varied according to the contrast of the original subject. Also, in ordinary photography, freedom of inspection during development may be of great assistance in obtaining the particular results desired.
II. Methods of Securing Visibility During Development.
The greatest possible visibility during development may be obtained by using an efficient safelight and by desensitizing the film.
1. Suitable Choice of Safelight.
In selecting an efficient safelight there are two factors to consider, (a) the sensitivity of the eye to light of different colors and wavelength, and (b) the color sensi
tiveness of the emulsion used. Mees and Baker1 have explained this matter clearly and defined safelight efficiency as the product of the vsiual intensity of the light transmitted multiplied by its safety for a given emulsion. The relation of these factors is represented graphically in Fig. I where curves showing the special sensitivity of the eye and the special sensitivity of typical photographic emulsions are plotted on the same scale of wavelengths as the transmission of the Wratten safelights. From the upper curve2 showing the spectral sensitivity of the eye it is evident that of a given intensity of radiation, the human eye is much more sensitive to green or yellow than to red or blue light. In fact the average point of maximum visibility for a large number of observers was at 560 mm.
Ordinary photographic emulsions, on the other hand, are sensitive only to the blue and violet, but when made orthochromatic they are sensitive also to green, and when panchromatic the sensitivity includes the red and is ex
1. C. E. K. Mees and J. K. Baker, "A Measurement of the Efficiency of Dark Room Filters," Phot. Jour. 47, 267, (1907).
2. K. S. Gibson and E. P. T. Tyndall, •■Visibility of Radiant Energy," Sci. Paper, Bur. Standards, No. 475.