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April, 1939] 1939 SPRING CONVENTION 469
"A Direct-Reading Photoelectric Densitometer;" D. R. White, Dupont Film Mfg. Co., Parlin, N. J.
A photoelectric densitometer has been built which shows the density of the area being measured on a direct-reading scale visible at a reading window. A density range from 0 to 3.0 is covered with a reproducibility of approximately ±0.005. A motor-driven circular neutral wedge is used as the balancing means, and the density scale marked on the wedge is read by a stroboscopic flashing light controlled through a special amplifier system.
"An Instrument for the Absolute Measurement of the Graininess of Photographic Emulsions;" A. Goetz, W. O. Gould, A. Dember, California Institute of Technology, Pasadena, Calif.
The objective determination of graininess is based upon the evaluation of a graininess coefficient G defined by the distribution function of the relative transparency fluctuations ( x = — ) : TT (x) = — • e x . The instrument con\ TmJ G
sists of a microphotometric recorder and a photoelectric integrator. In the former unit the ^-fluctuations of a uniformly exposed section of an emulsion are recorded with high resolving power and magnification (300 X} by means of a photocell. The amplified photocurrent is traced with a high-frequency galvanometer on 35-mm. film analogous to a large-scale variable-area record. Thus, a true representation of shape and frequency of the ^-fluctuations in the scanned emulsion area (width: 30 microns, length: 10 mm.) is obtained in black and white.
The distribution function of the fluctuations as well as the value of G is obtained by placing the record on a revolving drum and scanning it by an illuminated slit. The light transmitted by the record falls upon the photocell, the current of which is thus representative of the average occurrence of ^-fluctuations for a deviation (AT) from the mean transparency (Tm) determined by the position of the slit on the record. Hence, the change of the photocurrent represents the distribution function while the slit is moved across the revolving record. The scale on which the photocurrent is measured consists of a family of distribution curves (probability integral S-JT(X)'), each being characteristic for a certain G-value. The mechanical arrangement is such that a light-beam indicating the photocurrent selects and follows a particular curve while the slit is moved, thus determining whether or not, and if so to what extent, the ^-fluctuations follow the above distribution function. Furthermore, it indicates the graininess coefficient in terms of the above function. The taking of a graininess record of an emulsion (capable of up to 105 fluctuations) takes 3 min., its analysis 2 min.
"A Multiduty Motor System;" A. L. Holcomb, Electrical Research Products, Inc., Hollywood, Calif.
Various features of motor drive systems now in use by motion picture studios are described and the requirements for an ideal system defined. A recently developed system is described that will operate efficiently on alternating current for stage use or on direct current for location work. Many operating facilities are included which a survey has indicated should become a part of any ideal motor drive system.