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proceeded to expose the Infra-Red Type B with a similar technique, assuming that in order to obtain good results they had to underexpose this film. This, naturally, resulted in a print of insufficient contrast and shadow details. The superior quality obtained when using this Infra-Red type is principally achieved by the fact that it is possible to obtain a photographic change from day to night by the sole means of color correction, and that underexposure, with its attendant distortion, is not required.
Another obstacle encountered with Infra-Red sensitive emulsions is caused in some instances by the fact that chlorophyl, present in leaves of plants and trees, reflects Infra-Red rediation, and therefore objects of this nature are liable to be rendered too light in the print. It has been observed that this reflection of Infra-Red, particularly from green spring foliage, causes the appearance of a halo effect and thus creates the impression that the subject is out of focus. This apparent limitation can be counteracted to a great extent by calculating the exposure as short as possible, keeping in mind that over-exposure, naturally, emphasizes the halo effect. Another even better method consists of using lighter filters which will prevent the recording of excessive Infra-Red radiation in comparison to the remainder of visible red rays which are absorbed by using heavy filters.
In the beginning it might appear somewhat difficult for the cameraman to adjust his filtering technique to Infra-Red sensitive emulsions in order to obtain correct exposure and contrast under the various conditions with which he is daily confronted, but it should be considered extremely interesting and worthwhile that he acquire sufficient knowledge to avail himself of all the inherent possibilities this type can offer him.
As we know, the usual impression of scenes observed at night has numerous variations, beginning with the softness of dawn and up to the sparkling brilliance of, say, a full moonlight water scene. To reproduce this scale of contrast satisfactorily to the imagination of the theater-going public requires a full knowledge of the possibilities and limitations of the photographic methods by which the cameraman renders the desirable effect.
Fortunately, a certain basic knowledge sustained by practical experience, rather simply acquired, will serve as a satisfactory guidance for solving most of these problems, particularly that of obtaining the proper contrast for each desired effect. The negative contrast obtained in photographing night effects in the daytime on Infra-Red Type A or B can be varied from a steep to a flat gradation by simply changing from actual Infra-Red filters and deep-red filters, such as 88, 72, and 70, to light-red filters or dark-yellow filters. If filters are used which absorb all visible rays and transmit only Infra-Red radiation, the resulting negative will show a maximum contrast consisting only of intensely pronounced highlights and practically empty shadows. With lighter-red filters, such as the Wratten series between 21 and 29F, the contrast of the resulting negative and corresponding print will gradually decrease. Additional reduction in contrast can be accomplished by using yellow filters such as the G, Minus blue, and
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