The motion picture projectionist (Nov 1929-Oct 1930)

May, 1930 Motion Picture Projectionist 25 batteries are being made use of, because the current drains are comparatively high. These batteries, furthermore, are easily obtainable at reasonable prices; as they are not moved after installation, there is not much danger from the many connections necessary to wire them into the circuits. On truck recorders the battery requirements are varied. Potential batteries can be used provided the current drain is not too high. At present, the tendency has been toward the use of a number of 45-volt "B" battery units, but these have their objections because the connections between them may work loose. Horizontal Cylindrical Rear Shutter SINCE the advent more than a year and a half ago of the Motiograph Model H mechanism with its horizontal cylindrical type of rear shutter, and in view of the fact that since then other manufacturers have adopted the idea of locating the mechanism shutter between the light source and the film, much controversy has arisen regarding the merits of "between the light source and the film" location and many requests have been made for data published some time ago on the horizontal cylindrical shutter of the Model "H" mechanism, the first to recognize and offer to the trade the now unquestionable and proven merit of this type of shutter. Primarily, the Motiograph shutter was designed for the important function of eliminating the heat from the film. Heat on the film was fast becoming a serious problem. Constant demands for more light on the screen brought out more powerful illuminants including high intensity reflecting arcs, adding more heat on the film along with the increase in light. With the increased heat on the film came the attendant difficulties of warped and buckled film which caused still further difficulties in connection with the reproduction of sound from the film. Three Distinct Purposes The rear shutter on the Motiograph Model "H" mechanism is different from all other types of rear shutters. Its design represents the conclusion of a long series of experiments with rear shutters of every type in an endeavor to obtain a type which would function best to attain three distinct purposes: To eliminate most efficiently the greatest possible amount of heat from the film; to provide a means of cooling the metal parts of OQWN CYLINDRICAL TYPE Figure 3 the projector adjacent to the film aperture, and to provide as well, if possible, an increase in screen illumination over the former type of shutter in front of the lens. The final selection as a result of these experiments was the now wellknown horizontal cylindrical shutter as pictured in Fig. 1. The shutter is positioned between the light source and film being mounted in a cast aluminum housing and rotating on ball bearings. Its action in intercepting the light beam and incidentally the heat was found by actual test to eliminate 62% per cent of the heat from the film. In this test, temperatures were recorded with approved electric recording instruments of actual heat at the film position. First, tests were conducted to determine the amount of heat on the film with a mechanism using the old type front shutter. Then with the same illuminant operated at exactly the same amperage the test was conducted with the Model "H" mechanism with the horizontal cylindrical shutter. It is interesting to note that a small variation in heat on the film was recorded at different speeds with the horizontal shutter positioned between the light source and film, whereas the heat on the film with the old type front shutter was, of course, constant at all speeds. The result of the tests showed heat on the film with the old Motiograph horizontal cylindrical shutter, used on Model "H" Figure 1 type shutter at 1,486 degrees whereas the average taken of the different readings at different speeds showed the horizontal shutter reduced the heat on the film to 922 degrees less, or 564 degrees, as against 1,486 degrees, or 62% per cent. Aperture and Film Heat This efficiency in eliminating the heat from the film is due to the action of the two vanes or blades of the horizontal shutter which are so arranged that the light beam is cut off in a horizontal plane from top and bottom simultaneously during the full film movement period, and again during what might be termed the flicker interception at that period when the film is stationary before the aperture. Thus it will be seen that the heat from the beam is prevented from reaching the film during the entire period of film movement and again during a portion of the time while the film is at rest. It being allowed to reach the film only at two short intervals, once when the film has come to a complete stop before the aperture and again after the flicker interception and until the film starts in motion again. The second purpose of reducing the heat of the metal parts of the projector adjacent to and including the aperture is accomplished by a unique construction of the horizontal shutter itself and the construction of its DISC TYPE Figure 4 housing. It is well to remember that there is a distinct difference between the terms "heat at the aperture" and "heat on the film." By "heat at the aperture" is meant the heat on the aperture plate itself and the adjacent metal parts whereas "heat on the film" is the actual heat applied to the film. Reference to Fig. 2 will show that the design of the rotating shutter is such that its ends are angled similar to the blades of a fan but each end of a different pitch; in addition are shown air disseminating vanes, all of which are designed to function in connection with the shutter housing to provide a forced air circulation for cooling of the aperture and the adjacent metal parts. Forced Air Circulation This forced air circulation does not blow air on the film since any such air blown on the film would be drawn through the heated light beam; it has, in fact, an exact opposite effect. The shutter housing is attached to the film gate in a manner to provide air ports between it and the film gate. In the film gate itself are other air ports. The construction of the hori