16-mm sound motion pictures, a manual for the professional and the amateur (1949-55)

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SENSITOMETRIC CHARACTERISTICS 29 plan to discontinue the manufacture of nitrate base film for use in 35-mm, and to substitute the new safety bases. This step will do much to remove the fire hazard always present where nitrate base films arc used. Emulsion Hardness Emulsions are hardened during manufacture by a process similar to the process for tanning leather; this treatment reduces the tendency of the emulsion to soften and stick at high temperatures and humidities. Release print fine-grain films are especially hardened during manufacture to provide maximum service in use. Hardening agents may be introduced at quite a number of points in the film manufacture and use cycle ; hardening is often introduced at more than one point. Some of the points where hardeners may be introduced are : (1) Prior to coating of the emulsion upon the base. {2) Before development or during development. (3) Between development and fixation. (4) In the fixing bath. (5) After fixation. Hardening is especially important if film is to be processed at elevated temperatures (above 70° F.) or if the film is run in a camera, printer, sound recorder, projector, or other machine at high temperatures and humidities. Sensitometric Characteristics To evaluate the properties of photographic materials requires numerical measurement; the analysis by means of suitable measurements is known as sensitometry. For convenience in analysis, the relation between the blackness of the developed silver image and the illumination used to provide the exposure is measured by means of the relationship of the common logarithm of the opacity of the image to the common logarithm of the exposure. These functions are defined as follows : 1 Density = log10 Opacity = log10 Transmittance Transmittance where : Transmitted flux Incident flux Because of the variations in the amount of light diffusion that occur in practice, measurement of the transmitted flux and of the incident flux is not a simple matter. The incident flux may be diffuse, semi-diffuse,