The Cine Technician (1943 - 1945)

48 Edited by A. E. Jeakins THE CINE-TECHNICIAN .May— June, 1944 TECHNICAL ABSTRACTS Effects of High-Intensity Arcs on 35mm. Projection (E. K. Carver, R. H. Talbot and H. A. Loomis', S.M.P.E. Journal, July, 1943). Tlic study of the effects of high temperature arcs on 35mm projection shows that screen-image sharpness is affected by changes in the intensity of the heat on the film in the gate aperture. The him does not lie flat in the projector gate but takes different positions at different temperatures. The behaviour of the film during projection was studied by cutting away a part of the gate and taking high speed Cine-Kodak pictures (about 1500 frames a second) of the film as it passed the aperture. The pictures show that most films enter the gate with a slight positive curl (emulsion side concave) and then develop a negative curl during the instant they are exposed to the heat of the arc. This change of curl is caused by the expansion of the emulsion layer under the heat. The effect of the change of curl on the quality of the screen image was studied by taking high speed pictures of the screen during projection of a test roll. The pictures show that each frame comes into view out of focus and gradually becomes sharper until just before the pull-down when it reaches its maximum sharpness. Such pictures are of good screen quality if the projector is focussed carefully. Sometimes when the film is in a moist state, and when the heat from the lamp is excessive, trouble occurs with " in and out of focus " phenomenon, that is, the pictures goes out of focus for several frames. High-speed pictures of the film in the gate show that this is caused by the normal change from positive curl to negative curl being interrupted by a reversal back to positive curl ; so that just before the pull-down the film is curved towards the lens of the projector whereas it normally does the opposite. In this position it is outside the depth-of-focus range of the lens and produces an out-of-focus screen image. It is believed that this reversal to positive curl is due to a contraction of the gelatine caused by loss of moisture. As a result of their research the autlu >rs recommend that the heat intensity of the projection aperture should be kept below 1250°Fby using heat absorbing glass or other means, and thai prints should be dried thoroughly. A New Optical Printer (Linwood Dunn, American Cinematograplier, January, 1944). The Acme-Dunn optical printer claims to be the first commercially built all-purpose optical printer ; it lias been developed from years of practical experience in the studios. All operations and adjustments can be made from one position. The camera has been specially designed for opt printing and is an integral part of the machine. Effects such as lap dissolves, wipe-offs, slide-offs. etc., can be made to any length, either manualh or mechanically. Automatically focussed zoom shots, with a range of size from full screen to less than a 16mm frame, can be worked by turning i single wheel or mechanically by engaging witf the wipe-over drive. Printing speeds are 10, 20 30 and 60 feet per minute. Camera and project. have separate clutches controlled by a master distributor. The distributor can be set to make three colour separation negatives or to double ever second frame to change film speed from silent t sound. Skip frame work can be done while running continuously at any speed. The wipe-off device is driven by changeable sprockets which peimit a wide range of speeds; it can be moved toward or backward for any degree of softne>edge. Horizontal and vertical lens movement-; are calibrated to a thousandth of an inch by di;il indicators. A variable audible timer is fitted as an aid to timing manual operations. The 35min projector is inter-changeable with a 16mm 1 for blow-up work. A rear lens in the projector petmits aerial image work, so that paintings, matte-, animation and so on can be set at any distance behind the projector head and focussed at tie aperture. -For StuJio and laboratory equipment CanKrasJripodsJrin1in<j~?rocessiiKj plant... ana nr the solution of any technical problem concerning them the name thai matters is W.VINTEN LTD. NORTH CIRCUURRD.CRflKUWOOD.MW? —i »373