International photographer (Jan-Dec 1941)

l6fttM. dEpARTMEINT On the Subject of Camera Speeds Probably one of the most useful, but most neglected, controls on an amateur motion picture camera is the variable speed control. Many of the amateurs to whom we have spoken considered the adjusting knob a gadget that might just as well have been omitted; others who understood its diversification were frankly stymied by the many problems which its use might poise; and still others "rushed in where angels feared to tread" — and failed. But it can be used very successfully. Let us look first at the underlying facts. The standard silent camera speed is 16 frames per second, and the standard sound speed 24 frames per second. But we'll assume that you are the average amateur who does not intend to add sound on the film. (It is important here to distinguish between supplementary background music, such as phonograph recordings, with which the standard speed is retained, and actual sound recording on the film rack, which of course will require the 24-frame per second sound speed.) The shutter consists of a metal disc, approximately half of which is open at the exact instant at which the film remains stationery to permit exposure, synchronized with the intermittent movement of the film gate so that that open portion remains between the lens and the film only for the duration of the exposure. Then, as the metal portion of the disc moves in between the lens and film, shutting out the light and closing the shutter, the claws of the intermittent movement engage the sprocket holes of the film and pull it down the length of one frame. The next frame is then in position for an exposure. The shutter, of course, is rotating, and as the claws of the movement leave the sprocket holes to repeat their part of the process, the open sector of the shutter is once again at the photographic aperture behind the lens, ready for another exposure. The shutter sector (the amount of opening built into the disc) varies with the make of the camera, and depends largely CINEX Light Testers — Polishers used by all Major Studios. We are the sole Manufacturers and Distributors. Manufacturer of 16mm and 35mm Recording Heads, Developing Machines, Bipack Color and Black and White Printers, Rewinds. Special Machinery built to order. CINEMA ARTS-CRAFTS 914 No. Fairfax HE 1984 Holly-wood, Calif. Cable Addremi: "CINEBARSAM" upon the construction of the individual intermittent movement. In the Eastman camera the open sector is exactly one-half of the entire disc ( 180 degrees). And while it may frequently be less, it is never greater. Running at the standard speed of 16 frames per second, therefore, a complete revolution of the shutter will be made in 1/16 of a second. The time allotment for each individual frame, from the moment at which the intermittent movement starts the cycle and the claws engage the sprocket holes, through the time it is brought into place behind the photographic aperture, and until it comes to rest immediately below it, is 1/16 of a second. But we are interested only in one-half of this time — the 1/32 of a second interval during which the exposure is being made. The exposure, then, becomes directly dependent upon the speed with which the shutter is rotating, which, in turn, is dependent upon the speed of the camera; the greater the speed of the camera, the faster is the rotation of the shutter and the smaller the time interval during which the open sector remains in front of the photographic aperture permitting light to pass from the lens. Briefly stated, the greater the camera speed, the shorter the exposure, and the slower the camera speed, the longer the exposure. In order for action to appear at a natural pace on the screen, the projector and the camera must be run at the identical speed. We feel, therefore, that those amateur projectors which have been built with a rheostat control to permit an undefined speed of from five or six to 32 or 40 frames per second, constitute a hazard to the average amateur. Let's assume, however, that we are running at the silent standard. This is the speed for best results generally, because a speed greater than 16 frames per second is an unnecessary waste of raw film, and a speed of less than 16 frames per second will give an unsatisfactory flicker when it is projected at the slower speed. Now, operating the projector at the standard speed, any action that has been photographed at less than the standard speed will appear jumpy; and any action that has been photographed at greater than standard speed will be slowed down. For example, action consuming one second and photographed on eight frames of film in that one second, and then projected in onehalf second (at 16 frames per second) will appear abnormally fast; and conversely, if action is photographed on 64 frames during that one second, and then projected at standard speed, four seconds will be required for projection and the result will be slow motion. Now to put these basic facts to work. Perhaps the most frequent use the amateur will find for his variable speed control is the eight-frame speed when lighting conditions are such that the usual 1/32 of a second exposure will be too short. This is especially true of Kodachrome film when photographing sunsets, sunrises, etc. By slowing the camera down to eight frames, the exposure will consequently be lengthened to 1/16 of a second. It must be emphasized, however, that only scenes in which there is no action of any proportion, should be photographed in this manner. Occasionally it is desired to speed the action up, (the camera speed, of course, is slowed down) especially when photographing trains that are moving slowly, or horse races, or some athletic events, etc., particularly when a lens of long focal length is used and the angle is such that the action is coming directly ( or nearly so ) toward the camera. Long focal length lenses have a perspective that minimizes the effect of action coming toward the camera, and speeding camera action up will provide a more natural appearance under normal projection. But remember when using the eight-frames-per-second camera speed, that the exposure becomes 1/16 of a second, and be sure to use the next smaller stop when shooting in normal light. The result of shooting a normal scene at a speed greater than 16 frames per second is slow motion, when the film is projected at a normal rate of speed. If you are shooting a scene at, let us say, four times the normal speed, or 64 frames per second, to slow the action down to onefourth normal, be sure to bear in mind that the exposure now becomes one-fourth of 1/32 of a second, or 1/128 of a second, and the lens aperture will have to be opened up two stops, since each stop represents an increase of 100 % in exposure. For those interested in miniatures, etc., this control will be found to be a necessity. The swaying of trees, the ripples on the water, or any type of movement which would appear normal to the eye in the scene itself, will require faster camera speed so that the action will be slowed down to the point where the perspective of the movements in the minature matches those in the scene as it appears to the eye. Look closely at ripples appearing on water at some distance from you — do you notice how slowly they appear to be moving? And so, in all action from the swaying of leaves to mammoth explosions, you can give that distance to the scene by slowing the action down by means of an abnormal camera speed and normal projection. With judicious and intelligent handling, variable speed control will go a long way toward making your pictures more interesting. 20