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THE MOTION PICTURE CAMERA
of pictures necessary to produce upon the screen a moving picture which would not offend the eye by the flicker or pulsation due to the intermittent succession of light and darkness which produces the illusion of motion.
If the number of pictures thrown upon the screen is less than sixteen per second, the persistency of vision is not sufficient to carry the impression of light over the intervening period of darkness. Although the eye ma}»not be able to distinguish that the light is completely cut off while the next succeeding picture is being drawn Into place, there is an unpleasant pulsation commonly called "flicker," which is very fatiguing and annoying. By increasing the number of alternate dark and light periods per second the persistency of vision is able to bridge the gap between the successive periods of light thrown on the screen. As the flashes increase In their rapidity, they gradually merge Into a sensation of continuous light upon the screen without perceptible pulsation or flicker.
At sixteen pictures per second flicker is very perceptible so that many of the first cameras made w^ere constructed to take many more than sixteen pictures per second. Some of them made as many as sixty-four exposures and used a film four times the area of the present standard. With the small returns obtainable from the exhibition of motion picture films in those days, this rendered the expense of taking motion pictures almost prohibitive. The present narrow width of film was adopted to cut down expense.
It was also found that it was not necessary to take so many pictures to produce a satisfactory illusion of motion. However, flicker is unpleasant when the number of light flashes is less than thirty per second. Sixteen pictures per second produce a satisfactory illusion of motion so Instead of taking and projecting thirty or more pictures per second, a second blade or flicker blade was placed upon the shutter of the projection machine. This Intercepted the light for an instant while the individual pictures stood still upon the screen so that there were two flashes of light for each picture.
Any camera mechanism which records the successive pictures upon the sensitive film Is satisfactory — ^there Is no need of a flicker blade except to make a perfect record for reproduction.
It is highly desirable that the pictures be accurately spaced at
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