ILLUSTRATING THE PROPORTIONS OF LIGHT AND DARK PERIODS DURING PROJECTION IN TWO TYPES OF SHUTTERS.
1. Old single-blade type; caused a “flicker.”
2. Regular three-blade type; light evenly distributed. It is to be noted that while the picture is on the screen two opaque sections of the shutter eclipse the light.
In the last few paragraphs we have referred to the old type of shutter which caused a flicker, or unsteadiness of light on the screen. Nowadays a three-bladed shutter that nearly does away with an unsteady light is in general use. Its operation, approximately for the purposes of description is like this: It turns once in one-sixteenth of a second; one-sixth of this time is taken up with the moving of the film and the eclipsing of the light by one blade of the shutter. During the remainder of the time—five-sixths of it, the following takes place: the film is stationary and ready for projection, then two blades of the shutter and three of its open sections pass across the path of the light.
SECTION OF AN ANIMATED CARTOON FILM .
From this it can be seen that when the picture is viewed on the screen, there are actually two short moments when the light rays are cut off. This is not perceived by the spectator on account of the speed of the revolving shutter and the strong illuminant. Instead, the use of a shutter of this pattern evens the screen lighting by making an equal apportioning of light flashes and dark periods. With the old shutter there was one long period of light and one short period of darkness. It was this unequal distribution that gave rise to the flicker. At times, under certain conditions, a two-bladed shutter is used also.
A reel of film may vary in length for a short subject of fifty feet (or even less), to a very long “feature” of a mile or so in length. In width, the strip of celluloid measures one and three-eighths inches. Between the two rows of perforations that engage with the teeth on the sprocket-wheels and by which a certain part of the intermittent mechanism pulls the film along, are little rectangular panels, already alluded to, containing the photographs. Sometimes these panels are called “frames,” generally though, in the parlance of the trade, they are simply designated as “pictures.” They measure one inch across and three-quarters of an inch in height.
As noted above, these frames contain photographs of scenes that record, by changes in their action, the incidents and episodes of the story of any particular reel. In the case of animated cartoons, the frames on the film also contain photographs, but these photographs are made from sets of progressive drawings depicting the action of the characters of the animated cartoon.
In concluding this brief account of the modern motion-picture, the attention is directed, as the subject is studied, to a few details of the mechanism and to the general procedure that are found to be elementary features in nearly all apparatus used during the round of years that the art was developing. They are as follows: (1) A series of pictures—drawings or photographs—representing an action by progressive changes in their delineation. (2) Their presentation, one at a time, in rapid succession. (3) Their synthesis, directly upon the retina of the eye, or projected on a screen and then viewed by the eye. (4) Some means by which light—or the vision—is shut off while the change from one picture to another is taking place. (Projecting machines have been made, however, in which the film is moved so rapidly, and in a particular way, that a shutter to eclipse the light is not needed.)