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Cameras

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The principles of operation of modern professional motion-picture cameras are much the same as those of earlier times, although the mechanisms have been refined. A film is exposed behind a lens and is moved intermittently, with a shutter to stop the light while the film is moving. In the process, the film is unrolled from a supply reel, through the intermittent to the gate where the exposure takes place, and then on to the take-up reel.

Principal parts

Most cameras used today are of the reflex type. A partially reflecting mirror (beam splitter) is positioned in the door of the camera body or built into the lens itself with a parallel viewing tube. The mirror diverts to the viewfinder some of the light rays coming through the lens. This method's major drawback is that it takes away part of the light that would otherwise be used for the exposure. A much-admired viewing system that allows the full amount of light to reach the film is the rotating mirror shutter employed in the Arriflex camera. Light is reflected into the viewfinder only when the shutter blade covers the film as it advances to the next frame. This arrangement, however, is not wholly free from objections. Chief among these is that the arrangement opens a return path for light from the viewer's eyepiece to reach the film. The eyepiece must fit snugly around the eye while the viewfinder is in use, and the finder must be closed completely while it is not in use. In addition, since the camera shutter is closed only once per frame, the image will be subject to a distinct flicker, to which the cameraman must adjust himself. Some cameras incorporate a "video assist" or "video tap" wherein the viewfinder image is electronically fed to a video monitor or video recorder, thus allowing evaluation of the take by videotape replay.

Focusing has also been a perennial problem for the motion-picture camera. On the camera the position of the lens is precisely indicated on a calibrated scale. The actor's location on the set was formerly marked on the floor and the exact distance to the camera measured with a tape. The actor moved to previously marked places, and an assistant to the cameraman, called a focus puller, or follow-focus assistant, kept the lens in adjustment. Various electrical devices have now been introduced for remote adjustment by the assistant. Where a through-the-lens finder is used, focusing can be done directly, using the viewfinder image. Also, experienced cameramen can estimate distances quite closely.

The camera is often supplied with electric motors to perform miscellaneous functions, such as to provide smooth rotation (panning) of the camera or to change the magnification in a zoom lens (or change lenses in a turret). The camera is normally provided with footage indicators to indicate the amount of film left unexposed and with frame counters used when it is desired to superimpose a second exposure. There can also be an "inching knob" to reposition the film to a given frame for multiple exposures. When the camera is used at a speed different from standard, a tachometer may be provided to indicate the actual speed. The cameras that have so far been described are for the standard 35-mm film. Cameras for 65-mm film are generally quite similar, though heavier. The 16-mm professional camera may differ from the 35-mm in the form of its case, in its use of a spring-operated film drive, and in its method of film loading, as a result of its development from a former amateur camera. On the other hand it may be a smaller version and have the same features as the 35-mm model by the same manufacturer.

Camera supports
The camera must be mounted on a substantial support to avoid extraneous movements while film is being exposed. In its simplest form this is a heavy tripod structure, with sturdy but smooth-moving adjustments and casters, so that the exact desired position can be quickly reached. Often a heavy dolly, holding both the camera and a seated cameraman, is used. This can be pushed or driven around the set. When shots from elevated positions are to be used, both camera and cameraman are carried on the end of a crane, also on a dolly. In some cases the assemblage is smoothly driven to follow the action being pictured, such as movement along a street. If the surface being traversed is not smooth, rails, resembling train tracks, must be laid on the floor or ground for the dolly. The camera may be freed from the tripod or dolly and carried by the operator by means of a body brace and gyroscope stabilizer. One such support is the Steadicam, which eliminates the tell-tale motions of the hand-held camera.

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