Agfa motion picture topics (Apr 1937-June 1940)

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The Graininess of Photographic Emulsions by Dr. Alexander Goetz and W. 0. Gould California Institute of Technology The following instalment supplements three previous articles in this journal which describe the nature , the effect, and the measurement of the graininess of photographic emulsions. In Part III the construction of an instrument for the objective determination and analysis of this property of the emulsion by means of the graininess meter has been described, which has been constructed at the California Institute of Technology with the aid of the Agfa Ansco Research Fund. This instrument has, meanwhile, been applied to the analysis of various types of emulsions, be described and discussed as follows. Part The Graininess of Different Emulsion Types Tt lias been shown previously that ^the graininess constant G was chosen in such a manner that its values can be expected to be representative of the subjective impression of imohomogencity realized by the observer of a sufficiently large section of a photographic emulsion. The subjective impression as such, of course, varies with the observer, with the nature of the optical system for observation, with the color of light, etc. It is thus rather interesting to compare the graininess records obtained from different types of emulsions with each other as well as with the subjective impression gained from it. This purpose requires the comparison of different emulsions under approximately the same density as the graininess is known to vary considerably with the number of grains in the emulsion. Some of the results obtained shall IV. Figs. 1 -a to 1-f represent reproductions from graininess records of six different types of emulsions which are true representatives of negative and positive material used for professional and amateur purposes: a. ) Material for lithographic reproductions (density: .46) G = 39 b. ) Positive film (density: .47) G = 57 c. ) Sound recording film (density: .50) G = 63 d. ) Process emulsion for purpose of reproduction (density: .45) G = 59 e. ) Panchromatic emulsion of medium sensitivity (density: .41) G=93 f. ) Panchromatic motion picture film of very high sensitivity ( density : .47 ) G = 1 05 * *(The values of G are multiplied by the factor 1000 in order to avoid the use of decimals. This process is equivalent to an expression of relative 17