Sound Motion Picture Technology

The cameras actually used in the motion picture studios are beautiful pieces of engineering work, costing several thousands of dollars, and are distinctly heavy and complicated. When used for the photography of sound motion pictures, the cameras are specially silenced, or are covered with sound-proof casings, re ferred to as "blimps." They are supplied with several view-find ers, by means of which the scene can be viewed and properly focused on the film. The lenses are carried in a rotating turret or in changeable lens mounts, so that lenses of different focal lengths can be used on the same scene without the camera being moved. Many of the cameras are also fitted with auxiliary appara tus by which "dissolves" and "fades" can be made, and by which portions of the scene can be masked out. Some cameras are ar ranged to take pictures at many times the normal speed of 24 per second. When pictures taken above the normal speed are pro jected on the screen, everything appears to move much slower than normal. If the pictures were taken at eight times the normal speed, the action would be reproduced at i/8 the normal speed, since the rate of film movement in all theatre projection machines is fixed at 9oft. per minute, or 24 pictures per second. If it is de sired to show a subject running at extremely high speed, the cam era is arranged to take pictures at a speed below normal so that if the pictures are taken at 12 frames per second, or 5o% of the standard speed, they appear to be moving at twice the normal speed when they are reproduced in the theatre. "Slow motion" photography is used for analysis of motion, and both "slow motion" and "high speed" photography are used to produce inter esting and absurd effects.

Lenses.

The lenses used in motion picture cameras are almost invariably of large aperture, f/3.5 being about the minimum for the standard lens, while frequently greater apertures are used up to a maximum of f/1.5. The standard focal lengths are tin. (5o mm.) and Sin. (75mm.) although for special work, lenses of longer focal lengths are often used, 4-in. and 6-in. lenses being common. For photographing wild animals, etc., very long focus lenses are often used, it being possible by the use of a very steady tripod and an auxiliary support for the lens to use as great a focal length as 17 inches. All of these lenses are of the anastigmatic type. Every type of photographic objective, including tele-objec tives, is used in motion picture work. (See PHOTOGRAPHY : Apparatus.) Studio Lighting.—Before the advent of sound, the studio sets were illuminated chiefly by mercury vapour tubes and arc lamps. These were eliminated due to noise problems, and now a great preponderance of illumination is obtained by the use of large in candescent tungsten filament lamps. These lamps are rated in kilowatts instead of watts, as is the ordinary household electric lamp. The usual sizes used on a motion picture set have a capac ity of I, 2, or 5 kilowatts and a total of 6o kilowatts is used even on a small living-room set. They are used in banks for general

lighting, and also in specially designed reflectors and projection systems for spot lighting to accentuate the high spots.

The use of three-colour colour photography increases the amount of light required on a motion picture set many times. It is not economical or practical to secure this increased amount of light with the tungsten lamps, and arc lamps are generally used on colour pictures. These arc lamps differ from those used in the days of silent pictures in that they are "sound-proofed" so that they cause a minimum of objectionable noise. These silenced arc lamps are also used in black and white photography where a very strong beam of light is required to "high-light" some portion of the set.

Some lighting equipment accompanies the production unit even when work is being done outdoors. Special aluminium, silver, or gold surfaced reflectors are used when sunshine is available; otherwise, the usual incandescent lights are used. Special gasoline engine-driven generators, which have been sound-proofed, are the source of power.

Development and Printing

expo sure in the camera, the negative film is chemically developed. This is done on continuous machines (see Pl. XIII, fig. 4), the old rack and tank method having been made obsolete by the exacting requirements of present day photography and sound. In the machines, the film passes continuously through tanks or tubes where it is successively developed, fixed, washed, and finally en ters a cabinet where it is dried. The primary advantage of devel oping machinery is uniformity of development and accuracy of control, as well as ease of handling and rapidity of development. Some laboratories operate on the basis of giving individual treat ment to each scene of picture, in which case a test section from the end of each scene is developed first, at normal time, and in spected to determine the best development time. Scenes requiring more or less than normal time are then spliced together and sent through the machine in groups according to the time required. Other laboratories prefer to standardize the time of development and vary the contrast by controlling the lighting of the scene.

The developers used for picture negative and variable density sound negative in practically all modern laboratories are of a fine grain type, with a base of metol and hydrochinon, the customary sodium sulphite, and an alkali, generally borax. In the picture developer, a small amount of potassium bromide is added, but is omitted in the sound track developer. The average time of devel opment for picture is seven minutes at 65° F. (i8° C.), and for sound track apprcximately four minutes at the same temperature. For variable width sound track, the contrast or gamma must be very much higher than is required for variable density sound, and generally a developer of the same type as required for positive prints is found satisfactory.