International projectionist (Jan 1959-Dec 1960)

Aperture-Filing for ' Keystone' Effect: An Outline For Proper Procedure Many moons ago, as the Indians say, I read an article in IP relative to the proper procedure for the filing-out of aperture plates so as to correct the "keystone" effect — that is, a "chopping off" on the top of the screen image. I got a sort of "fuzzy" effect on each side of my screen image. I pose this question because it has arisen from time to time in discussions with other projectionists. Herbert Newman IA Local 542, Marinette. Wis. THE "keystone" shape of the aperture image caused by excessive projection angles can be overcome by properly filing out aperture plates which are under size in width (such as the G-2302. G-2303, and G-2304 Simplex X-L plates for non-anamorphic projection, and the G-2412 and G-2413 plates for CinemaScope) . Filing the apertures does nothing to correct keystone distortion and elongation of the picture image itself. Such distortion can be overcome only by the use of special projectors manufactured in Europe. Normally, the length of the bottom edge of an undersize aperture should be increased to normal width (0.825 inch), while the final length of the top edge depends upon the amount of keystoning to be overcome. The two sides are finally filed to straight, smooth edges which will slant in toward each other slightly. An aperture thus filed out has a keystone shape, but this counteracts the optical keystoning caused by projection angle to give a rectangular aperture image on the screen. But, as stated above, the picture, itself, still will be distorted. Procedural Suggestions There are several ways to determine the amount of filing needed to imparl the proper shape to the finished aperture. The correctly-masked blank screen illuminated by the stage strip and footlights may be photographed on a piece of unexposed raw 35-mm negative placed in the aperture of the projector and exposed tor a few seconds. The film, when developed, shows the screen as a black trapezoidal area of the correct size and -hape. Most projectionists, however, file apertures by trial and error, frequently testing the results by projection on the screen. Another good method is to place a regular rectangular aperture in the projector and measure the width of the image along the top, then along the bottom, of the screen. If the width at the bottom of the image is 24 feet, and the width at the top is 22 feet, simple arithmetic reveals the exact dimensions required for the filed-out aperture. Assuming that the length of the bottom edge of the aperture will be increased to standard width (0.825 inch), multiply 0.825 by 22 (top) and divide the answer by 24 (bottom). This gives 0.756 inch, the required length of the top edge of the aperture (which will show on the bottom of the screen, of course). Marking this out on the aperture plate, connect the corners by accurately scribed lines and file out very carefully. Avoid owerfiling (brass is soft!) and test from time to time by actual projection. The sides of the projected image will not be "fuzzy" if the aperture has been accurately dimensioned and the sides filed out smoothly. Use a very fine flat magneto file for finishing. Move the screen masking in at the sides, if necessary, to cover up the actual projected image of the aperture. LETTERS TO THE EDITOR Lamp Filament' Warm-up To the Editor of IP: Relative to the article on 16-mm film by R. A. Mitchell (IP for December last ) , no one will dispute his approach to the gradual heating of lamp filaments of the 750-1000 watt type. In the old 30volt, 900-watt days one manufacturer used a control device consisting of a long, finely-threaded rod which left the projectionist exhausted by the time the advanced position was reached. However sound, the slow-heat approach is impractical. With the improvement in high-temperature metals and better filament suspension within the lamps, we have encountered very little trouble from this source during the past ten years. As many as 100 people may operate a 16-mm unit in the school system of a city of 50,000 population. Lamp blisters may be lessened by running the projector motor for one minute after projection ends. Allison Albee Albee Enterprises, Rye, N.Y. Kudos for R. A. Mitchell To the Editor of IP: The article on screens in IP for November last (Are Lenticulated Screens Practical?" by Robert A. Mitchell) is the first that has ever made me feel disposed to write and congratulate the author. It is refreshing to see figures which have some revelance to the facts of life. I have been developing lenticular screens and surrounds since before World War II. I produced the first lenticular silver screens, which made large screen TV possible, for the Rank Organization in the late 1940's, and I put the first curved lenticular screen in the world in at the Festival of Britain, where we showed 3-D in 1951. Many of my screens were flown to America in the first flush of 3-D. I find Mr. Mitchell's forthright views on most subjects near to my own. The pity is that the few personalities who could and should influence trends towards the future life and prosperity of our industry do not read Mr. Mitchell's sort of article. So, we continue with a policy of drift. J. L. Stableford Stonebridge Park, London, England Salute From the Antipodes To the Editor of IP: We have only lately formed the "I.C." (Inner Circle) in Brisbane, Australia, but our parent bodies in Sydney and Melbourne have done 20 years or more of good work in the projection field. Technical and social activities are carried out by this body of men who work within the Union. Meetings and lectures are monthly. Another of our activities is rostering our members and providing a show for spastics, orphanages, and an occasional hospital ward once a month. We want you to know how much we appreciate the IP for the excellence of its technical articles and also its outspoken policy and fairness on controversial subjects. Firm fellowship greetings and best wishes for the coming year from: Inner Circle of Projectionists Queensland, Australia 12 INTERNATIONAL PROJECTIONIST • FEBRUARY 1959