International Review of Educational Cinematography (Jan-Dec 1934)

298 THE CINEMA IN EDUCATION In projecting the film, account was taken primarily of the dimensions, and not of educational requirements. This does not apply only to foregrounds and individual parts of the whole. Another objection to excessively small dimensions is that any damage to the film, whether in development or in use, and any grain of dust that may have got between the layers of emulsion in the prints bulks much larger in projection than it would in the case of films of larger dimensions. From what has been said above, it is clear that the 1 7.5 mm. size is more satisfactory for educational purposes than the 1 6 mm. If the decision as to the size of the film had rested with the school, it would have chosen the larger size. Since, however, the majority of the more competent producers of reduced size films, and also the printing establishments and exigent amateur cinematographists, have pronounced in favour of the 1 6 mm. film, and since numerous experiments with reversible films, or simply with films converted from the normal to the reduced size, have shown that the 16 mm. film is adequate for all grades of education, it has necessarily been accepted as the school film. It is only a wide use of films which can lead to gradual reduction in their cost. To make it possible to use any of the reduced sizes as desired in a school, projection machines have been constructed which can deal with all the different sizes, provided certain of their component parts are changed. These machines, however, are merely a makeshift, because, owing to their light capacity, they are properly adapted to only one size, and this could be avoided only by choosing very complicated and expensive machines. Perforation. — The object of perforation is to allow the film to be unwound by means of sprocket wheels the teeth of which interlock and rapidly run off a strip of film. The devices for unwinding the reels of film put perforation under a considerable strain. If the lower edge of the perforations is damaged, the picture is no longer steady. If the damage is very serious, the film can no longer run regularly through the projection machine. The perforations may be either at the sides if the film or in the middle, between the pictures. Lateral perforations may be either on both sides or on one. A double perforation naturally tends to make the film last longer, and a two-sided pull is more regular than a one-sided pull. In consequence of these factors, the normal-sized 35 mm. film is perforated on both sides, and on every side of each picture there are four holes to receive teeth, in the form of a Maltese cross. The 16 mm. film is also perforated on both sides, but has only one hole on each side of each picture, corresponding to the tooth on the sprocket-wheel. The half-normal-sized film has the same perforation as the normal film, but on one side only. 16 mm. sound-films are also perforated on one side only, in order to leave room for the sound-track on the other side. This, of course, reduces the life of the perforation. The 9.5 mm. film receives a perforation in the centre, between the pictures. Consequently the width of the pictures has to be reduced by the diameter of the perforation. In the case of small-sized school films, the perforation should be on both sides, so that the film can be kept longer in use. Perfection of the The main requirements Image. 0f an educational film are connected with the perfection of the image, because anything that is to be exhibited for instructional purpose must be absolutely clear and sufficiently luminous, and the tones must shade perfectly into one another. The first precautions to comply with these requirements must be taken at the time of shooting the film. Above all, there must be sufficient light. The light come from the proper direction and must be very carefully graduated. Outdoor pictures, taken by daylight, should only be shot in the right position relative to the sun, and in good weather ; for other pictures — especially