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ing are numerous. The photographing of all of the color records at one time is the obvious means. A single objective must be used if the views are to be free of parallax. The use of two or three objectives with multiple exposures is feasible in overcoming fringing, but introduces parallax.
Campbell (English Patent No. 2,786 of 1913) suggests a way of using multiple lenses and overcoming parallax by blurring the portions that are "out of register" and the scheme appears workable, the main drawback being the fact that the short focus lenses usually employed for cinematograph work cannot be used.
However, the camera employed to date by one company takes negatives in which the pairs of records are in sequence on a single strip film taken singly without parallax and it is a fact that 95% of the negatives are without noticeable color fringe. Color fringe is due to the fact that successive stages of the action do not register as regards color, a moving white object particularly being preceded and followed by stripes of pure color when projected.
It seems to me that a camera taking single records at each exposure satisfies the commercial aspect, especially as the negative is workable in connection with the commercial positive film.
The negatives are photographed through gelatine color filters and in the two-color system consist of blue-green and red-orange so that one record is made through blue-green followed by a record taken through the red-orange. It requires both of these records in each frame of positive to make up our complete color record of the commercial (16 pictures per second) film. Consequently twice the footage of negative is required in recording the scene as compared with black and white negative of the same scene and this holds good with all systems or schemes with the exception of the "d" (Dufay) film mentioned above.
Exposing 32 pictures a second through color filters is some job too. However, an increased exposure period in the camera plus a very important improvement in the filters makes the work quite practicable.
Filters
These are colored gelatines, usually mounted between two optically flat glasses. They have the property of passing certain colors and absorbing certain other colors. A complementary pair of taking filters will, for example, allow the orange and red to pass through one of the pair and record those values on the film in the final form of developed (reduced) silver, while the green and blue light reflected from the objects being photographed will pass through the green-blue filter. This explanation, however, is only partially true, as the conditions only hold good at certain intensities of light. Either of the filters in the pair will record white light and will pass red-green and blue light if of sufficient intensity. It is this necessity of recording the whites and greys and still preserving the separation or isolation of colors that is responsible for the Raleigh-Kelley Patent U. S. A., No. 1,217,425 of 1917.
By this means, to each exposure through the color filter is added on the same image area a neutral exposure which has very much the same efl^ect as the addition of the grey print in quadricolor printing, and while this about doubles the exposure, it is also found to wonderfully
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