Reel and Slide (Jan-Sep 1919)

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REEL and SLIDE 27 II! Illlllllllllllllllllllllllllllllllllllli Edited by M. BERNAYS JOHNSON (Projection Division Westinghouse Lamp Company) g Questions on projection will be answered by this department provided § addressed and stamped envelope is enclosed. Address Projection, Reel S and Slide Magazine, 418 South Market Street, Chicago, 111. iiiiiiiiiiiiiiiiiii!iiiiiiiiii;iiiiiiiiiiiiiiiiiii Projection Announcement Commencing with this issue, the projection department will be conducted by M. Bernays Johnson, who is in charge of the projection division of the Westinghouse Lamp Works, and who enjoys a wide reputation as a designer and creator of electrical effects and devices, for which he was awarded the Grand Prise, Gold Medal, blue ribbon, and five diplomas at the International Exposition. His designs and ideas have been instrumental in bringing the science of incandescent projection up to the high standard it has attained today. The incandescent equipment used so successfully by the Presidential Party on the S. S. George Washington was installed under Mr. Johnson's supervision. Mr. Johnson will contribute a series of articles, which will be plainly written so that the student or layman who should have occasion to handle the various types of presentday projectors, will be enabled to know what the purpose and function of the various parts are and what manipulations are necessary to operate these machines and obtain the best results. Questions pertaining to projection and installation will also be answered. THE SCREEN One of the problems that confront the small exhibitor of motion pictures is the screen and next to the projector that is the most imperative because the problems of the film are taken care of by the manufacturers and producers. Especially in schools and colleges a suitable screen that will reflect the proper light with as little eyestrain upon the pupils is of course desired. There are three kinds of screens that are within the reach of those in this field. These are, first, the coated, plaster wall which, in the opinion of some experts, is unequaled for the small projector, especially the ones using the incandescent lamps. Second: The muslin screen, which requires a frame upon which it is tightly stretched and tacked. It is treated with some compound to make it stretch and while it is in this loose, wet condition is tacked upon the frame work and placed in the sun to dry and when dry it will be as smooth and tight as a drum-head. * • * The third is that of the commercial variety, which consists of a heavy sheet of canvas, upon which is applied a coating of aluminum paint, Simplex projectors installed aboard the S. S. George Washington for the entertainment of the Presidential Peace Party. Description "on page 30. or some similar compound, known by various trade names, but all contain more or less aluminum paint. These screens come ready finished from the manufacturer and cost about 75 cents per square foot. The reason for this apparently high price is the skilled labor and the patented processes that are used to apply this aluminum coating or surface, as it is absolutely necessary that this coating be so evenly applied that there are no brush marks or they will cause the piceture to be streaked. To the layman it will seem possible to use a fine camel's hair brush, or an air spray, but after seeing a number of such attempts that look to the eye to be fine and then see the poor results obtained when a picture is flashed on the screen, the need for skilled workmanship is apparent. I will say that if anyone desires a silvered screen, buy it from the manufacturers, they know how, and it will be much cheaper; but if one cannot afford such a screen or desires to make his own, here is how it can be done: First, either find out the size of the picture your projector will throw or else look in some standard projector catalogue or handbook and consult the table giving the size of the picture and the desired throw; then make your screen frame nine inches bigger than your picture; this allows for a black border. The frame can be made or procured from a carpenter, of cypress or white wood, 54 inch thick and 3 inches wide, known as "batten," used by scenic artists and theatrical people. After the frame has been made, buy some bleached muslin; this can be secured in almost any width, and cover your frame, but not permanently; simply put in a few tacks so that the muslin covers the frame smoothly. Now procure a good white paint and paint the surface. You will notice that as soon as the cloth becomes saturated with the paint it will become loose and sag. Now lay the frame flat upon the floor and take up the sag, stretching as tight as possible and tack securely in place. Put the curtain in the sun to dry, and when dry it should be as stiff and tight as a drum-head. To finish the screen use white calcimine, give it a good, even coat; this will give excellent results, but requires a little touching up from time to time to keep its appearance bright and fresh. Now that the screen is painted, place it in position and project the light from your machine upon it, and with a pencil draw an outline of this light upon the screen. This will serve as a guide. Now procure some dead black shellac. This can be made by securing some orange shellac and mixing a quantity of lamp black with it. Apply this all over that portion of your screen that is not covered by the light from the projector. It is preferable to paint about an inch or two on each side into the field of light; this will bring out better the contrast between the black and white and make a very prettily framed picture. The plaster wall screen : A number of schools have tinted plaster walls. A section of wall is selected where all can see the picture in a class room. AH that is necessary is to project the light upon the desired spot and after determining the location, pencil it off and that surface covered by the field of light a good coat of calcimine and paint a black border around this, as previously described. Another novel way that will serve very well as a temporary screen is to select a section of the blackboard, rub the surface upon which projection is desired with white chalk, the kind used to write upon the blackboard. Rub it smoothly upon the surface and it will serve surprisingly well. * • * We are having difficulty with our lens. First, the picture on the screen is too large. Is there any way we can adjust the lens for smaller pictures? Second, the lens doesn't always give the same sharpness on the screen. — A. R. C. Answer: You have an objective lens of too short equivalent focus. Write to any motion picture supply house, giving them the following information, and for a small sum they will exchange your present lens for one better suited to your conditions. Tell the length of throw measured from film to screen exact, width of picture you wish to show and make and type of machine. If the trouble expressed in your second question is not due to dirt on your lens system, check up on the following: Does your lamp house always remain in the same position? Are your condensers reasonably tight in their holders? Are your tension shoes properly adjusted so that the film is held rigid while passing by the aperture? How do you figure the cost of operation of a lamp that is using 50 amp. 220 v. D. C. ? Also as to rheostats when you have figured loss in wattage? What is the essential difference between spherical and chromatic aberration? They both seem to me to have the same characteristics. The objective lens contains the meniscus and bi-convex. What are the names of the other two and what is their proper positions in holder? Jacob Allen. Answer : You pay your light bill in kilowatt hours, that is, so many thousand watts used for so many hours. To find the cost of operation of your lamp take the voltage of the line, which is 220, multiply it by the number of amperes used, or 50; 220 X 50 = 11,000 watts. Divide by 1,000 to get the number of kilowatts and multiply by the cost of the current in cents. If, for instance, you are paying 8c per kw.-hr., your lamp is costing you 220 X50^ 1,000 X 8 = 88c per hour. The rheostat makes no difference in the cost of operation. What current your lamp doesn't use is converted into heat by the rheostat. When parallel light rays after passing through a lens do not come to a single focus on the principal axis of the lens, but instead cross the axis at different points, the lens is referred to as having "spherical aberration." If light rays are passed through a spherical lens, the white light is broken up into the various colors of the spectrum, so that instead of securing an image of pure white light, several other primary colors are visible, usually on the edges of the image. "Spherical aberration," then, has to do only with the meeting point of light rays; "chromatic aberration" means color separation. The objective contains the following lenses, given in the order met by a light ray leaving the condensers: Bi-convex, convexo-concave or meniscus, plano-concave, biconvex. We are using a Powers 6-A machine, which is a hand drive. The machine seems to give an excessive amount of noise at the intermittent sprocket. Is this due to its being a hand-driven machine, and if so, why? Motor drive machines never give any such trouble as this. I put on a new intermittent sprocket, but it didn't help any. Arthur Wilson. Answer : The fact that the machine is hand driven should make no appreciable difference in its operation. The probable reason for a certain amount of noise at the intermittent sprocket is the presence of wear on the pin, cross and cam. You had better return the entire intermittent to the factory and have them go over it thoroughly and put it into shape. Your trouble is not in the intermittent sprocket as was proved by the continuation of the noise after a new intermittent sprocket had been added. What should govern the choice of lenses? A. J. K. Answer: The choice of lenses must depend largely upon your distance from the screen and the size picture which you desire to project, but also to a certain extent on the illuminant used. With the arc lamp or the gas-filled Mazda, a smaller diameter objective will work more satisfactorily than with the acetylene or other low power light. Where anything but electricity is used, it is recommended that the 2 7-16-inch diameter or "half size" mount objective be used, even though it costs a little more. The results will more than justify the additional expense and it will be more than worth your while to have the outfit which will give you the best possible pictures.