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334 CINEMATOGRAPHIC ANNUAL
The use of filters as a means for controlling exposures requires a profound knowledge of the sensitivity characteristics of the film, with reference to the source of light used to illuminate the subject.
It is quite evident that such technique requires highly technically trained operators who have acquired the ability of putting their technical knowledge at the service of their artistic conceptions.
Since the user of 16 millimeter films will mostly strive for a true representation of the subjects he has chosen, perfect sharpness of the picture and as great a depth of focus as possible are most desirable. Hence the amateur will obtain better results in controlling exposure by operating the lens diaphragm, which, as it is well known, controls the "depth of field" of the lens.
This fact is so strongly established and recognized that 16 millimeter cameras are not equipped with shutters of variable aperture, and manufacturers strive to produce cameras having as great a shutter aperture as possible.
Fig. 3. The shutter of the Bell & Howell FILMO Camera model 7 0 which has an angular aperture
of 216 degrees.
Lenses at large aperture should be used by the 1 6 millimeter users only when the light conditions are such that the greatest possible exposure is necessary to obtain any result at all.
Another advantage is derived by the user of 16 millimeter film through the use of as small a diaphragm opening as it is compatible with the light conditions, and that is. that for lenses of as short a focal length as one inch, the depth of field is so great for a small aperture, that for all practical intents and purposes the lens can be con