Movietone Bulletin (July 1928)

“MOVIETONE SWUECE TIN | _ Published | in the interest of the Movietone Projectionist ye Fox CASE CORPORATION 460 WEST 54 ST..NEW YORK VOLUME I, No. 29 JULY 21, 1928 The Optical Train OVIETONE projectionists will do well to remember that motion picture projection is about nine tenths an optical problem. It is the controlling of the action of a powerful light beam by means of a train of lenses, or by means of a mirror and train of lenses. The selection of the various elements of a projector optical train is a thing to be approached only with adequate, accurate knowledge and great care. Much faulty projection is due to wrongly selected projector optical train elements, or to their faulty adjustment with relation to each other. However, even though all optical train elements be correctly selected and adjusted, it still must be remembered that there will be a heavy light loss if each of the various elements be not kept scrupulously clean. ‘ If you have a Fifth Edition of the Bluebook of Projection—and all movietone projectionists should have one—turn to page 141, Volume 1, and you will discover that the Professors Gage, eminent authorities on such matters, place the loss of light by reflection from both polished surfaces of a lens (meaning both when the light enters and leaves the lens) at from 4 to 5 per cent., provided the surfaces be perfectly clean and well polished. If the surfaces be not well polished and (or) dirty, then the loss per surface may be as much as fifteen per cent. Some authorities place the loss much higher, with a minimum of six per cent. per surface for clean, well polished surfaces. More Projeciionisis of the Land of Penn Mr. J. C. Ansell, W. P. Craig. in the State Theatre, Uniontown, Pa. All these boys from the brotherly-love domain are evidence that not everybody out there digs coal or makes rails for choo-choo cars to run on. (above), and Mr. They are projectionists You therefore may readily see the importance of keeping the lens surfaces and the mirror surface scrupulously clean. Condenser lenses should be cleaned every day. The outer surfaces of the projection lens and the port glass, if one there be, also should be cleaned daily, regardless of whether or no they look clean. To clean lenses effectively I would recommend a solution of one half each of denatured or wood alcohol and water. Select a perfectly clean, soft cloth, such as, for example, an old cotton handkerchief, dampen it with the solution, wipe the surface of the lens and polish quickly with another similar, dry cloth—with a soft-finish paper napkin or with a wad of high grade, soft-finish toilet paper. The latter is especially good, because you can hang a roll of it up convenient for use. If the lens be entirely free from oil and cold, an effective method for cleaning is to breathe upon it and polish quickly. Warning: After cleaning a lens surface be very, very certain not to let your finger tip touch its surface. A finger mark faint enough to be entirely invisible as one looks through a lens, may and probably will injure the definition of the screen image seriously, provided it be on the surface of one of the projection lens elements. What’s that? You know all that? Well, probably you do, but just the same I find a surprising number of not-too-clean lenses in projector optical trains; also lenses with faint finger tip marks on them. So be careful! Be very certain your projector optical train is exactly what it should be, both as to the selection of its various elements and their adjustment one to the other, and with regard to cleanliness. Clean the condensers or (and) mirrors, the outer surfaces of the projection lenses and the port cover glasses before the first show starts every day. It is the only right way. It may be all right not to let your left hand know what your right hand is doing, except, of course, when you are turning the fader at change-over.