The Cine Technician (1953-1956)

March-April, 1953 THE CINE-TECHNICIAN 27 has long recognised that the sense of depth and dimension in sight is as much a psychological as physiological phenomenon, depending in large measure on experience and the subconscious evaluation of visual " clues," such as the relative size, velocity or overlapping of objects which the brain translates into terms of distance and direction. As many of these clues occur on the fringe of human eyesight, surrounding the central area of sharp focus, peripheral vision plays an important part in the total sensation of full-dimensional sight. The average range of man's vision is 165 degrees horizontally and 60 degrees vertically; Cinerama closely approximates this visual field by reproducing an image 146 degrees by 55 degrees. The effect on the viewer, confronted and all but surrounded by the same optical frame of reference as in real life, is not only the immediate illusion of three-dimensional vision but the sense of actually taking part in the action on the screen. As well as being " wrapped in action," the Cinerama audience is also " bathed in sound." During production six separate omni-directional microphones are used, strategically spotted around the scene of action, each recording on its own track the sounds picked up in its particular area. In the theatre, these sound tracks, imprinted side-by-side on a single strip of magnetic film, are separately amplified by eight speakers placed behind the screen, at the sides of the auditorium, and even at the rear of the theatre. Consequently, sound comes to the audience from the direction of its original source; when an actor on the left side of the screen speaks, his voice emanates from that spot; when a plane zooms across the screen the noise of its engines follows its image — if it flies towards and over the camera, the spectator hears the sound as it approaches, as it is overhead, and finally as it recedes in the distance behind him. A seventh sound-track, combining the other six, is utilised as a safety measure against the possibility of momentary failure of one of the single tracks which might result in a, " dead spot " on the screen. Before Cinerama could become a practicable reality, an entirely new industry had to be developed to devise equipment for the new medium. Because Cinerama uses a larger frame size and more frames per second than the ordinary motion picture (26 as opposed to 24). none of the existing production and projection instruments could be used. Instead of the conventional 2,000-foot reel, Cinerama uses an 8,000-foot one; instead of regular range-finders, movieolas, and other accessories essential to the production of a finished film, new models, three times the usual size, had to be specially built. The curved screen presented a problem, too, as it was soon discovered that light from one side of the screen was reflected to the other, interfering with the image. This difficulty was licked by designing a screen of 1,100 vertical strips of perforated plastic tape, arranged like the louvres of an enormous Venetian blind, which bounced reflections off behind the screen. Another technical obstacle that had to be surmounted was the visibility of the dividing lines between the three images on the screen; to remove them Cinerama engineers evolved an ingenious device known as a " jiggilo " — a sawtoothed attachment that oscillates within the projector, " fading " the edges of each picture so that no sharp division between them is discernible. Because absolutely accurate, frame-by-frame synchronisation is essential to the successful operation of Cinerama, an intricate servo mechanism, christened " Startmark," was developed, which keeps all three films — and the sound track — running in unison, with an engineer at a central panel adjusting each projector by remote control. The sound head runs at the same speed as the projectors and acts as the master to which each projector is kept in frame-for-frame sync speed. This is accomplished by the selsyn synchro, mechanically driven by the sound head, feeding a similarly connected slave synchro on the projector with a signal. If the projector rotates this slave synchro out of phase with the sound head, a signal is generated and is amplified by the servo amplifier to activate one of the two relay contacts, forward or reverse, to supply power to a small correction motor. This correction motor is mounted to a differential gear box, through which the projector motor drives the projector head, and either assists or retards the drive motor until the projector synchro is in phase with the sound head. Each projector fills 48 degrees or one-third of the screen. The lenses of the projectors must be adjusted to give equal magnification on the screen. The pictures overlap approximately one degree. To prevent this matching area from having double light intensity, compared to the rest of the picture, reciprocating saw teeth immediately behind the film plane at the projecture apperture decrease the light by 50 per cent from each projector, thereby giving normal intensity on the screen and a smooth blending from one screen to the" other. The projector head was made by Century and is similar to that company's standard model " C " head. The film sprockets are larger and the intermittent has been made stronger to accommodate the six sprocket frames of the Cinerama picture. The film has also been made to run at 26 frames per second to do away with the flicker to which the human eye is more susceptible on its peripheral vision. The film is standard 35mm. with a six-sprocket frame. The dimensions of the frame are: lin. x lsin. Together with the increase from 24 to 26 frames per second and the increase in frame size, the film travels at 146 feet per second, compared to the standard speed of 90 feet per second. The film when printed is edge-guided and is edgeguided in the projector to minimise jump and weave on the screen. With three separate pictures being projected, if the movement of one is up while the other is down, the overall picture would seem to be jumping twice as much as it actually is. Furthermore, a standard picture is usually masked by a curtain, and there is no reference as in the Cinerama picture for the audience to notice the jump oi' weaving motion. Hence edge-guiding is very essential to the one-picture effect if three disjointed pictures are to be avoided on the screen. The projectors have frame-mounted counters. The film is edge-numbered from the start mark. Thus, in case of a film break in any one of the projectors or the sound head, the projectionist who has the break threads up on any frame with an edge number and reports this number to the console operator, who in turn informs the other projectionists of the number, whereupon they roll their machines to that number on the counter, and all the machines are then in sync and are ready to roll. The sound and picture consoles are operated by one man. The sound console has gain controls and patching facilities; the picture console has an intercom to each of the projectors and sound head. The projectors are started remotely from this position and the light intensity of the three screens is constantly adjusted from here. There are also differential syncros in the line between the master at the