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up into the shoulder section of the curve.
Naturally we can get very similar results with over or under-development. As a matter of fact, the ‘gamma strips’’ used in laboratories today are all given an accurately standardized, normal exposure. Then the deviations from normal densities in the different steps will serve as a measurement of the development. These methods are equally useful w i t h negative or positive film.
Practical Application
While all of this has a most obvious connection with laboratory work, it has also an important relationship to the everyday work of the practical cinema tographer.
Speaking generally, it is the cinematographer’s aim to produce in monochrome as natural a rendition of the scene as possible. For this, he finds it best to utilize the full gradational range of the him material he is using, in order to have available not onlv the extremes of highlight and shadow, but the fullest range of delicate intermediate tones. In addition, for obvious practical reasons he will get the best results when he knows that all of his gradations in lighting — which is to say gradations in the exposure of all of the details of his scene — will be represented by directly proportional gradations in the tonal values of his picture.
In scientific terms, this means that he must utilize the region of his film’s sensitivity in which exposure-values and density increase proportionately — that is, the straight-line portion of the H. & D. curve. For faithful reproduction. this must be true not only of the negative, but of the positive as
well. This gives him what we like to call a normal result.
At times, of course, strictlv normal results may not be wanted, as in scenes v hich for dramatic reasons require strong, contrasty treatment or, on the other extreme, extremely flat treament. The same results, as most of us have at some time or other learned to our sorrow, can be produced unintentionally through errors in lighting, exposure or laboratory treatment.
Illustrating Gamma
To demonstrate these points in a practical way. the accompanying illustrations were made from photographic tests, showing the visual and sensitometric effects of both normal and distorted lightings. A wax figure head was used for the sake of uniformity. The lightings were simplified approximations of normal, of overflat and of ultra-contrasty close-up lightings. A sensitometric or gamma strip was made on the same roll of film as each of the negatives used for illustration, and corresponding positive strips were made from these. The strips were made with a standard sensitometer, and their densities read with a standard densitometer. The curves obtained from the negative and positive strips were plotted in the usual manner.
In order to bring out the very practical relationship between sensitometric values, densitometric readings were taken on opposite sides of the face — the cheek-bones, to the precise —in both the negative and the positive. These, in turn have in the illustrations been connected by the solid lines to the respectively corresponding densities in the sensito
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