KINEMATOGRAPHY The art of photographing objects in motion and projecting the images upon a screen. It derives its origin from a toy called the " zoetrope " and depends for its results on what is known as " persistence of vision." When light is reflected from a moving object it forms an image on the retina (or sensitive plate) of the eye, and creates a nerve current which passes along every one of the fibres which receive the image and collectively carry the impression through the optical nerve to the brain. This sensation may be divided into four periods : First, a latent period which is almost instan taneous, and during which nothing seems to happen ; second, a very short period, estimated at less than of a second, during which the sensation reaches the maximum ; third, a much longer period, nth to of a second (varying according to the power of illumination) during which the sensation slowly diminishes ; and, fourth, a short period of decline, during which the effect dies away. It is found that in the case of a moving object on which attention is directed the fourth period remains unnoticed, owing to the fact that a new image takes up the place of the old one before that period begins. Prof. Tindall estimated the time of persistence of an impression on the retina to be nth of a second, that is, the impression remains for Ath of a second after the source of excitation is removed. Upon this all kine matograph apparatus is based.
The kinematograph camera and projecting apparatus are described under the heading " Kinematograph." The three chief requisites to final success are : (i ) A photographic emulsion sufficiently sensitive to receive latent impressions at the rate of sixteen per second ; (2) optical systems capable of forming the negative images in the camera and the positive image upon the lantern screen ; and (3) mechanical means for suitably trans lating the films through the camera and after wards through the projector.
The emulsion is supported on celluloid cut into ribbons in. wide, and in lengths of about i3o ft. The inner portion of the surface, i in. in width, is devoted to the pictures, the margins being used for the perforations by means of which the film is held in position during its progress through the camera or projector. Each image is i in. wide, and in. high, there being sixteen pictures to i ft., and four per forations on each side per picture. Slightly thicker celluloid is used for the positive film than for the negative, the former being sub jected to more wear and tear than the latter.
Having decided on the type of camera to be employed and the make of negative stock film to be used, the operator may proceed to work much in the same way as he might when taking ordinary snap-shot photographs in an ordinary magazine film camera. The negative stock film can be obtained in rolls of 15o ft. in length, ready perforated, and supplied in sealed tins, in which it is wrapped in lead sheets and light tight paper. The magazines A B (see D, p. 319) are detached, and the unexposed film opened in the dark-room, with ruby light, and placed in magazine A, the centre of the roll being slipped over the bobbin w. The starting end of the film is drawn through the small aperture at the corner of the magazine, and the lid secured. The short length of the film projecting at the corner serves as lead film to facilitate drawing out, when it is desired to thread through the camera mechanism just before actual operations. When about to make the exposures, the side of the camera is opened and the film threaded as indicated at D (p. 319), taking care to arrange for the loop at and at as. The bobbin x has a clip which holds the end of the film securely. The lid of the magazine B is, of course, removed during these operations, and the length of film extending from C is unavoidably fogged. The operating handle of the camera should be turned a few times in order to make sure that everything is working properly ; then the lid of B and the side of the camera may be closed. It now remains to see that the picture is sharply focused and, to do this, the handle should again be turned so as to bring an unexposed portion of the film opposite the exposure aperture R, and at the same time cause an open section of the shutter N to arrive in a line with the lens.
By removing the cap s from the sight tube Y, the operator may now have a view of the image on the film. If a focusing scale is provided on the lens itself, this operation is, of course, unnecessary; a separate view finder is provided on the camera. See that the cap s is replaced. The handle must be turned at the requisite speed, and as the mechanism is generally geared to make eight exposures for each complete turn of the handle, two turns should be made per second. Too fast camera operating will result in abnormally slow motion of objects in the projected picture, and vice versa. The most important point is the question of steadi ness, for if the camera has been allowed to vibrate during the work of turning the handle, no afterwork can rectify such an error. Manu facturers supply very rigid and somewhat heavy stands for the camera. The screw holding the camera to the stand should be very tightly fas tened. (See also " Theatrical and Kinematograph Photography.") Development of kinematograph films is carried out in precisely the same way as that of ordinary film negatives ; but some special appliances are necessary. The frame B is one. The pins top and bottom serve to hold the film in place, it being wound in spiral fashion and secured at each end by clips or drawing-pins. The emulsion side is turned outwards, so that only the celluloid surface comes into contact with the frame. A tank sufficiently large to take the frame is provided for the developer, another for the fixing solution, and a third for washing purposes. The latter is furnished with a siphon overflow so that proper circulation of the water is secured ; a tap provides a constant supply of fresh water at one end of the tank, the overflow siphon being situated at the opposite end. The washed film is wound on a skeleton drum A in spiral fashion, and placed in a warm room free from dust, and kept rotating for fifteen minutes. When the emulsion is thoroughly dry, the cleaning process is carried out, all finger marks being polished off from the celluloid side by means of a pad of soft material fixed to a bench over which the gelatine surface may pass without injury. A hole cut in the bench, through which the light of an incandescent electric lamp is directed upwards, enables the cleaner to detect smears and other marks. The film is wound up into coils by means of special winders.
The positive film is made by contact printing from the negative. Special machines are pro vided for the purpose, in which the action of the mechanism is approximately the same as that in the camera. Exposed positive stock is developed, fixed, washed and cleaned in the same manner as the negative.
If through accident a subject becomes broken in the middle, cutting out should be done so that when the two ends are rejoined, pictures follow on consecutively as before the accident. The ragged part of one end should be cut away exactly at the juncture of two pictures, and the end to be joined thereto should have an *th portion of a picture left on. The gelatine on this *th part should be removed, leaving the bare celluloid exposed. Film cement is then applied with a brush to the scraped-off portion, and this is quickly laid against the celluloid backing of the piece to be joined, firmly pressed, and allowed to dry. The cement dries within a few seconds after application. See that the perforations on the overlapping portions of the film exactly register. The blank spacing of film subjects is a source of many troubles if not correctly carried out. There are four perforations each edge to each picture and any length of blank film joined between succeeding subjects should correspond in length to a given number of complete pictures ; other wise, it will be necessary to make an adjustment in the machine when projecting.