The Cine Technician (1939)

Auo-. -Sept., 1937 THE CINE-TECHNICIAN 85 which the intermittent assembly is driven. By substituting a pair of elliptical gears, the intermittent movement was accelerated so that the pull-down period occurred in 52: of the cycle instead of the usual 90°. Using this, in combination with a 45° covering blade and a 30° flicker blade, a gain of 59 per cent, was made in screen illumination. However, it was thought that this was too severe on the film and a second pair of elliptic gears were prepared which gave a more moderate acceleration to the pull-down mechanism, and accomplished the movement of the film with a 68° interval. Using with this a covering blade of 60 and a slicker blade of 40°, a gain of 44 per cent, was realised. However, unless there are certain changes made in projector design which will compensate by reducing the stresses occurring in the pull-down operation, it is doubtful whether application of even this mild degree of acceleration to the Geneva movement is practical. The Powers movement, however, because of the smooth acceleration, offers possibilities for a quicker pull-down. The proper size for the shutter blades was arrived at empirically by progressively increasing the width until there was no noticeable flicker or travel ghost on the screen at the ordinary brightness level. Advantage was taken in these experiments of the fact that the perceptibility of both flicker and travel is less as one proceeds to lower levels of illumination. If it should later be found necessary to increase the shutter blade slightly, it would represent a loss of only a few per cent. A further discussion of the subject of projector mechanisms is believed outside the scope of the present paper. Although the work done so far must be regarded as merely preliminary, there seems to be ample grounds for believing that more can be done in a practical way to recover a considerable part of the light lost at the shutter. In this connection, moving the shutter to a position very near the film plane so as to give quicker cut-off of the light beam would be a worth-while step. However, in the small neighbourhood theatres, probably no change in projector mechanism would be needed in order to get sufficient light. Print Density Another loss of light occurring in the ordinary projector is caused by the minimum photographic density allowable in making the print. Because of the excellent tone reproduction obtained with the lenticular process, it is possible to make the print density lower than that of a corresponding black-and-white print by approximately TO. This gives a 25 per cent, increase in picture brightness. Summary of the Gains Made It was pointed out above in connection with the filters that the maximum filter transmission combined with that of the lenticular support was in the neighbourhood of 17-6 per cent, which corresponds to a factor of 5-8. This is the factor by which the screen brightness must be increased in order to equal that of corresponding black-and-white projector. The gains made and discussed above may be summarised as follows : — Table I. Factor. 1. Increased relative aperture (f/2-5 to f/1-6) 2-31 x 2. Reduction of shutter loss 60°-40° shutter, 68° pull-down 1-44 x 3. Tower print density, by TO 1-25 x Product of all the above gains 4-32 x (Continued on page 87) IF YOU WANT A CINE CAMERA USE SHAW JONES DAY & NIGHT f L NEWMAN SINCLAIR CINE CAMERA HIRE SERVICE EIGHT NEW AND COMPLETE OUTFITS AVAILABLE For List of Equipment see Leaflet enclosed in this issue. 49 Greek St., London, W.I 'Phone: GER. 6716 (Day & Night)