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CHAPTER III
16-Mm Film and Its Characteristics
" Motion picture film* is a thin flexible ribbon of transparent material having perforations along one or both edges and bearing a sensitized layer or other coating capable of producing photographic images." This definition confines motion picture film to a film in which the imagebearing portion is on the surface ; the definition bars the use of the term in connection with Ozaphane and similar films that utilize a light-sensitive diazo dyestuff distributed uniformly throughout the film.
Although this chapter will deal almost entirely with silver-emulsiontype films, the diazo dyestuff film type should be mentioned, since it holds future promise for commercial use in certain conditions of application. Diazo dyestuffs may be manufactured inexpensively; many show resolving power in excess of the best that has been obtained with silveremulsion films. With the dyestuff distributed uniformly throughout the base, the films are not as seriously affected by surface scratching and abrasions as are silver-emulsion films. Diazo films are photographically slow; they require great exposure to provide the photographic image. Since the image is developed in ammonia gas, there is no need for alternate wetting and drying of the film ; better dimensional stability can be obtained with the same base material. Copying with a single exposure results in a photographic image of the same highlight-shadow aspect as the material being copied; a positive copy image is produced from a positive image in single development. Most diazo films have high contrast. Although early diazo films gave poor reproduction of highlights and shadows, newer diazo films are being devised that show promise of overcoming many of the early reproduction handicaps.
Silver-Emulsion Films
Although silver-emulsion films have been in use for more than 50 years, very little has been published on many important phases of film
* According to definition 1.1 of American Standard Nomenclature for Motion Picture Film Used in Studios and Processing Laboratories — ASA Z22. 56-1947, the term ' ' film ' ' may be applied to unexposed film, to exposed but unprocessed film, and to exposed and processed film.
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