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CHAPTER VI
The Problem of 16-Mm Emulsion Position
Introduction
As pointed out in Chapter III, a conventional 16-mm motion picture film consists essentially of an image-recording emulsion approximately 0.001 in. thick, coated upon a mechanical support — called the base — which is approximately 0.005 in. thick and is usually clear. Thus, the image is confined to the emulsion which is only one-sixth or so of the total thickness of the film.
What is more important is that the image is located on only one of the two surfaces of the film base. This almost obvious fact which is implicitly presupposed and rarely stated explicitly is the crux of the emulsion position problem despite the fact that there are other known considerations that are not presupposed. One such consideration relates to the use of a form of light-sensitive film called Ozaphane* (one of many trade names) in which the light-sensitive, color-forming, diazo dyestuffs are mixed with the base-material components prior to their manufacture into sensitized-sheet photographic film. Since these dyestuffs are uniformly distributed throughout the base, it would be advantageous from the optical engineer's point of view if the base material could be made very thin, about 0.001 in., so that for practical purposes the photographic image would be located in a thin plane rather than spread out through a relatively thick solid as it would be viewed by a light beam that traverses the image-registering film. From the optical engineer's point of view, the coated emulsion of the conventional film is already only about 0.001 in. thick, and the design advantage of reducing either the emulsion thick
* It is interesting to note in passing that Ozaphane films are developed in ammonia gas. Such development has a number of advantages which include:
(1) A positive is made directly from a positive without need for chemical reversal.
{2) Since no water is used for developing solutions, the dimensional changes due to development are small compared with conventional silver film developing methods.
(3) The image is a colored dye that is substantially grainless and has a high resolving power.
(4) Sensitometrically, one of the films has a shoulder but no toe to its density — log exposure curve.
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