International projectionist (Jan-Dec 1950)

Projector Shutters: A Symposium By R. H. CRICKS Technical Editor, "Ideal Kinema" ONCE again I have to take up the cudgels on behalf of a British projector as opposed to the views expressed by Robert A. Mitchell in International Projectionist — although this time, it is true, it is on a somewhat trivial matter but one that merits correction. In an article on projector design, Mr. Mitchell makes the statement that B.T.H. (British Thomson-Houston) claim as original the dished shutter used in their Supa projector. I am sure that B.T.H. know as well as Mr. Mitchell that this type of shutter was used many years ago: Mr. Mitchell attributes it to pre-war European projector manufacturers; my own recollection surely goes back considerably farther — in fact, to the early Motiograph projector. A feature that is claimed by B.T.H. to be original — and is, indeed, the subject of a patent — is the supplementary vane which Mr. Mitchell omits to mention but which principle is plainly shown in the sketches which must have been available to him as he wrote. In the open position of the shutter the vane is parallel with the rays of light and casts no appreciable shadow. As the shutter turns, the vane intercepts more and more of the light. The effect of this vane is that the angle needed by the shutter to cut the beam is reduced from the 19 degrees possible with a plain 7inch dished shutter to 14 degrees — this, of course, occuring four times per frame. The dished shutter has the advantages over other high-efficiency shutters in needing no complicated gearing and in operating quite close to the aperture. By FRED MATTHEWS Motiograph, Inc. MR. CRICKS' comments, flattering as they are to Motiograph's long history of enterprise in the projection field, are complimentary indeed. There have been many so-called comparative tests made to determine the light-transmission efficiency of various shutter assembles. If some published results of such tests appear biased, one can always turn to Mr. Mitchell's articles for a * "Notes on Modern Projector Design," (I, II, III) by R. A. Mitchell; IP for May, June, July, 1956. t "Projector Shutters: Design, Performance," by R. A. Mitchell and Larry Davee; IP for August, 1950. SPRINGBOARD FOR THE APPENDED HIGHLY INFORMATIVE SYMPOSIUM ON PROJECTOR SHUTTERS WAS PROVIDED BY THE RECEIPT FROM FRED C. MATTHEWS, OF MOTIOGRAPH, INC., OF A RECENT COMMENTARY BY R. H. CRICKS, TECHNICAL EDITOR OF IDEAL KINEMA (LONDON, ENGLAND), ANENT THE RECENT SERIES OF IP ARTICLES BY R. A. MITCHELL ON MODERN PROJECTOR DESIGN, WITH SPECIAL EMPHASIS UPON VARIOUS TYPES OF SHUTTERS.*! MR. CRICKS LEADS OFF, IS FOLLOWED BY MR. MATTHEWS, WITH LARRY DAVEE, OF CENTURY PROJECTOR, ROUNDING OUT THIS STIMULATING DISCUSSION. breath of fresh air in a murky atmosphere. We feel that the Mitchell articles, in the main, are eminently fair to all concerned because of their objective quality, and the weight of our opinion in this respect runs to Motiograph's 54-years' history of building production or experimental models of projectors using every known type of shutter in a wide variety of positions. In 1908, Motiograph employed a small, single, rear conical shutter located almost flush with the aperture in our Opti DOUBLE REAR SHUTTERS SHUTTER "8 FRONT AND REAR SHUTTERS RESULTING LIGHT CUT-OFF IS THE SAME AS SHOWN ABOVE SINCE THE LOWER HALF OF THE LIGHT BEAM IS CUT OFF BY THE REAR SHUTTER V, AND THE UPPER HALF OF THE LIGHT BEAM, AFTER REVERSAL BY THE PROJECTION OPTIC, IS SIMULTANEOUSLY CUT OFF BY THE FRONT SHUTTER "B". SINGLE, REAR, CONICAL SHUTTER The accompanying discussion of projector shutters provides a welcome opportunity to service the scores of requests received for IP for August, in which it originally appeared, which could not be honored due to the rapidity with which the supply of that issue was depleted. INTERNATIONAL PROJECTIONIST • October 1950 11