Principles of cinematography : a handbook of motion picture technology (1953)

GENERAL TRENDS AND RECENT INVENTIONS 425 'Fantasound* system has only been installed in a very few American theatres and, because of this, the film 'Fantasia' was normally run as an ordinary sound film using the auxiliary track printed on the picture film and which was, originally, intended for use only in an emergency. Under these conditions the film could be reproduced by any sound system although, of course, the stereophonic sound effects would not be obtained. At the present stage of development it seems very unlikely that stereophonic sound reproduction will become widely used whilst such complicated installations are required in the theatres. (2) Improvements in Presentation (a) Flickerless Projection. Turning now to recent developments in the field of picture quality and presentation, it is interesting to note one of the many designs which have been introduced to maintain the screen constantly illuminated. It will be apparent that two main defects exist with the normal picture projector; firstly, the arc lamps are required to run at their present high intensity because a large proportion of the light is lost during those parts of the projection cycle which leaves the screen dark whilst the shutter is covering the lens. That this is true may be readily proved by running a projector with such a low powered illuminant that the machine may be safely stopped with the picture in the gate and with the shutter open. When this is done it will be found that the screen picture is considerably brighter when the machine is stationary than is the case when the shutter is running. The second point, which will only cause trouble in present-day projection if the screen brightness is not correct, is that flicker may be noticeable when very 'thin' prints are used or, in any case, if the observer should move his head from side to side. Assuming that intermittent film movement is necessary, it is still quite possible to obtain a constantly illuminated screen by re-arranging the order in which the pictures are printed on the positive film. It then becomes necessary to use a specially designed projector having two heads mounted one above the other. One suggested arrangement for such a film is shown in Figure 179, in which it is assumed that the two picture heads are mounted one above the other and in such close proximity that a free loop, fifteen frames in length, will exist between the two machines when both are correctly threaded. Let it now be assumed that the lower head is projecting frame No. 20, as indicated at position T, whilst the upper head is drawing the film forward to bring frame No. 21 into the gate, as indicated at position '2' (fifteen frames above position T). Since the two heads are connected 180° out of phase, light will be projected from the lower lens whilst the upper lens is masked off and the film in the upper gate is being moved forward. It should be noticed that two important points exist in the arrangement of this film. Firstly, frames to be shown consecutively are always printed fifteen frames apart on the film that is, frame No. 21 is fifteen frames further into the roll of film than frame No. 20, frame No. 27 is fifteen frames further in the roll than is frame No. 26 and so on throughout the entire film. The second point is that alternate frames are only printed with the normal two frame separation. For example, Frame No. 22 is only two frames away from frame No. 20, whilst frame No. 21