Besides standard-size film, amateur cinemato graphy and educational films employ various films of reduced, sub-standard size. These are usually made with a cellulose acetate base,' and such of them as are specially intended for amateur use are coated with a reversible emul sion, so as to avoid the somewhat high cost of printing a positive.
898. Cinematograph Cameras. With the ex ception of certain amateur instruments which, with various additions, can be used for taking views, printing them, and them, cinematographic apparatus is highly specialized, and among the cameras exclusively intended for taking views, three classes may be recognized at the present time- (a) Apparatus for drama subjects, comprising numerous accessories for such effects as the gradual passage from one scene to another, double exposures, masks, vignettes of increasing or decreasing size, etc. These cameras are always used on a rigid stand, often fitted with a panoramic head.
(b) Cameras for record and scientific cinemato graphy, topical films, etc. These differ from the preceding only by the omission of the special accessories for scenic effects. These cameras are generally used on a but sonic of them may be held in the hand or suspended from the operator's body by straps, being driven by a motor (spring motor, compressed air motor, etc.).
The normal taking frequency for cameras of these two classes was, for a long period, 16 frames per second (reduced to 14 for 9.5 mm. film). The necessity for giving to sound record ing a length of about 455 mm. per second has led to the normal running speed of 35 mm. film being raised to 24 frames per second. The handle of these cameras may be placed on the axis of one of the gear wheels, so as to record one frame per turn of the handle.
(c) Cameras for speed cinematography, used at the rate of about 240 frames per second. The resulting films, when projected at the normal rate (the called slow-motion projection), mag nify the periods of tune and render possible the analysis of movements which cannot be studied under normal conditions.' The mechanism of these instruments is very different from that of ordinary cameras, which, if worked at such speeds, would tear the film and would soon be damaged.' These instruments must be used on extremely rigid stands, to prevent the vibrations of the mechanism from causing a general tremor of the camera.
All these cameras may be actuated by an electro-niotor run either by current from the mains, in the case of studio instruments, or by means of a set of accumulators, in the case of cameras used out of doors. Devices have been
made for actuating the camera from a distance, especially in the case of the cinematography of wild animals in freedom.
Just as any rapid phenomenon can be slowed to any desired degree to enable it to be analysed, so also a slow phenomenon, difficult to perceive on account of its very slowness, such as the germination and growth of a plant, the evolution of glaciers and other geological changes, can be condensed into a very short space of time if the cinematograph record is taken at long intervals (such as an hour, a day, according to the more or less slow character of the phenomenon it is desired to represent), projection being effected at the usual speed.
899. Film Boxes. The unexposed film is loaded into the cameras in full daylight by means of removable boxes having, as a rule, a capacity of 4.00 ft. of film. These boxes, having served as suppliers of film, are then used as receivers of the exposed film.
The film boxes and the manner of placing them in the camera vary with different makes, so that only general rules can be given. In all cases where it is necessary to wind the film on a core special to the film box used, this winding must be done in a room free from dust, on a winder in perfect condition, avoiding too high a speed and excessive tension, which will produce static (§ 242) or friction markings (s; 199). The film box must be carefully cleaned before placing the spool of film in it, special attention being paid to brushing the velvet strips which main tain the light-tightness of the slot through which the film passes.
When placing a box in the camera, of which the film channel and the various parts have been cleaned, it is usual to have a length of 20 to 3o in. of film projecting from the box.' Its end is cut into a point, and it is first led over a supply drum and then into the film channel, where the claws engage the perforations, then on to another drum, a loose loop being left between the channel and each of the drums (some cameras have only one drum which both sections of the film pass over, covering an angle of about 120 degrees), and finally on to the core of the take-up box. By giving the handle a turn, it is seen that the film is correctly threaded and the take-up box and camera are then closed.