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UNTANGLING FILTER FACTS
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HAT is the advantage of using a filter?" a new movie maker asks. "And, while you are about it, tell me why you advise me to use 'color filters' with black and white film but not to use them with color film. It's rather confusing."
The answer is simple. Almost every scene that we photograph is full of color of many hues and shades. When we are using black and white film, we know that these colors will not be reproduced as colors, but as shades of black and white. What we forget, however, is that the degree to which some colors affect the film differs from the degree to which they affect the eye.
Some colors appear lighter on the film than they should, others darker. A light yellow may appear as too dark a shade of gray in the Mack and white picture, while a rich blue may appear too light. To overcome this, we use filters, pieces of colored glass or gelatine sandwiched between thin sheets of glass. We place these in front of the lens.
The simplest example of their utility is in the effect of the proper filter upon the sky. All of us have had the experience of filming a nice landscape or ocean view in which there are fat, billowing clouds, and then, after the film is processed,
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KENNETH F. SPACE, ACL
of discovering that the clouds had vanished.
This happened because the film was sensitive to blue, and the blue light from the sky made approximately the same impression on the film as did the white clouds. The eye could sec the difference between the blue and the white, but the monochromatic film could not. A yellow filter would have "held back" some of the blue light, and the clear sky would have registered as a darker shade of gray than would have the white, puffy clouds.
Since the filter itself is colored, it is called a "color filter." It does not cause any color to appear on the film ; it simply affects the degree to which certain colors register in the scale of grays, from white to black.
The most useful filters to the average movie maker are those intended primarily to affect the blue of the sky and thus to emphasize the cloud forms. A white sky is unpleasant on the screen, for not only is it unnatural looking to eyes accustomed to seeing blue skies as a darker color, but, also, the large area of white light reflected from the screen is glaring.
However, one can do other things with niters than to produce
a dark sky. Panchromatic film is sensitive to blue, yellow,
green, orange and red. By the selection of the proper
filter, we can make any of these colors appear in the
film as a darker shade of gray than they would have
■ done were no filter used.
We can be very subtle about it, if we wish. But, unless we are doing very specialized filming, we are interested only in getting a few attractive effects. Since this is so. we can reduce our filter requirements to just three — the yellow, red and green types.
Here is what these filters can do and how they can be used: [Continued on page 337]
A yellow filter was responsible for the handsome sky here
How, why, which and when are answered here