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THE DUSENBERY SYSTEM OF ESTIMATING EXPOSURE
H. Syril Dusenbery
IN ORDER to have an intelligent understanding on the subject of exposure it is first necessary to know just how the sensitive film emulsion records the image. We are all familiar with the fact that this image is directly dependent on the light that reaches the film, not only the amount of light, but the quality as well. When sufficient light reaches the film so that the image formed when it is finally developed is a clear and faithful representation of the original subject, it is said to be correctly exposed. Movie makers will find that with a little practise and experience this goal of correct exposure is not difficult to attain.
The only light that reaches the surface of the film when a picture is made is the light that is reflected from the subject itself. It should be remembered that regardless of the general brilliancy of the light, it is only that portion of it which is reflected by the subject that is effective. Naturally dark subjects do not reflect as much as white ones. For this reason dark objects require more exposure. Also a subject in the direct path of the light will reflect more into the camera than a similar subject receiving the light at right angles to it. The color of the light reflected must also be considered since the ordinary emulsion is much more sensitive to blue colors than to red. While the many factors that enter into the matter seem to make it quite complicated, in actual practise it is surprising how quickly the eye can be trained to judge the proper exposure necessary to obtain good screen results.
It is strongly recommended that the movie maker use an exposure meter until he has trained himself to judge light conditions accurately. Select any type meter that appeals to you and stick to it. Do not change meters continually. The Cinophot and Dremophot meters are particularly recommended as they actually measure the light reflected from the subject. These meters give accurate results even in the hands of a novice. By doing a little systematic testing, you can quickly learn the shortcomings and errors in the readings of your meter. The matter of personal equation enters to a considerable extent with many types of meters as no two people see things exactly the same way. It is, therefore, suggested that your meter be tested and checked against actual screen results.
To test any meter, take an average scene, a street for example, and determine the exposture (lens setting) with it under the given light condition. Jot this down for future reference. Now shoot a few feet of film with this recommended exposure. This done, change the lens setting to the next larger opening and shoot again. Then change the lens setting once more, this time making it the next stop smaller than that originally indicated by the meter, and again shoot a few feet of film. Make notes of exactly what you have done. When the finest]