Moving Picture Age (Nov-Dec 1919)

MOVING PICTURE AGE 27 PillllllllllllllllllllllllilllLlllllllllllllll^ Any questions pertaining to projection of films and slides | on the screen will be answered by this department. Address | "Projection," Moving Picture Age, 418 So. Market St., Chicago. ] If an answer by mail is desired, enclose stamped envelope. §j W :::' .ill'. miu: i,j:. : : : : , ,i|: ,|! . ,.;!r ., ' :,i:!: . ,;i' ';';■ ,;ii' ; :.: i;:. ;, r:i;,„ ,, , ,..;l,i...., ,.., ...,ni, .,,,1. .iii,,..;.,n, ::„.,. , ,i;,., ...,:i;:..,iiii;.;. , .; ,. iir;... ..: i ■ ...Mii;^ Projection REFLECTION OF LIGHT RAYS FROM THE MAZDA LAMP By W. R. Rutledge THE theory of the reflection of light from a given source to any specified focal point is one on which engineers entertain differences of opinion which would be very amusing were they of less importance. Some advocate the use of a spherical reflector for the purpose of centering the rays of a mazda lamp onto the aperture plate of a motion picture machine, others are strong in their advocacy of the mangin shaped mirror for the same purpose. Some projectionists have gone as far as to say that reflectors are unnecessary and that as good a picture can be obtained without them as with them. With all due respect to the opinion of the latter, they are wrong in their conclusions. The best use of the reflector is found in its function of concentrating the available amount of light on the aperture plate. Opinions differ materially concerning the amount of "stray" rays that can be gathered and concentrated, but there need be no argument whatever concerning the question of concentration from the focal point, when the reflector is of the right shape and dimensions and is placed in proper relation to both focal point and source of light. The superiority of the mangin is unquestioned when a photo-meter is used to measure the results of any comparison. With this reflector the light is not concentrated directly back again to the point of source, but through and around the source to the aperture plate on the machine, giving a maximum of both direct and reflected rays. With a spherical reflector in use the concentration takes place directly on the source of light (the lamp filament) when the reflector is placed in position according to the instructions usually sent out by those who are advocating the use of spherical reflectors. The surface of the mangin is more flat, has less convex, with the result that concentration takes place at a greater distance from the reflector and thus much nearer the aperture, which gives greater illumination on the plate. It also results in lessening the amount of heat that is concentrated on the filament of the lamp, as the secondary heat, caused by reflection, is less apparent, the most beneficial result of this being evidenced by longer life to the lamps. Some mazda devices are so constructed that the operator has no choice in determining the location of either light, reflector or focal point. All dimensions are fixed except that of distance between the machine and the screen, this important point being entirely to the optical lens to take care of almost automatically. This mistake is the result of a lack of thorough investigation on the part of the designer of mazda equipment. Too much is left to the element of "good luck" and the function of the lens is not clearly understood. It is the light behind the film that defines it to the lens, and the lens, when in focus to the screen will faithfully carry the definition to the screen itself. The amount of light that can be obtained from the 30-volt 30-ampere mazda lamp is not a fixed quantity, the amount depends on various factors that are readily controlled by the operator, when he is provided with suitable apparatus for projection. There need be no change made from the regular condenser system used with carbon projection, if they are suitable to proper projection at the distance and for the amperage now used, they will do very well for mazda projection. The distance between the light source and the condensers must be flexible, as must also the distance between the lamp and the mirror. Best results on the screen can be had when the projectionist has command of all the elements that go to make up perfect projection. The projectionist is not an automaton, but a living necessity in the booth and too much pains have been taken in trying to develop mazda projection apparatus requiring a minimum of mechanical intelligence in the booth. A device for controlling the voltage going into the circuit and regulating the amount of amperage used to illuminate the lamp, together with reasonably elastic appliances for placing mirror, lamp and condensers in proper focal relation to each other and the film, will, when used for their primary purpose, result in more uniform illumination on the screen, quieter and better pictures than can possibly be had with light derived from a carbon source. The necessary apparatus to secure these results consists of a good transformer and lamp socket. There is as much difference in transformers as in the men designing them. Select a transformer that is designed to carry the type of lamp you intend to use, one of safe and economical capacity and capable of minute regulation of amperage as well as of voltage, for it is amperage, not voltage, that gives luminosity and so the regulation must be very close in order to obtain highest efficiency from the lamp without burning it out prematurely. Next select the most suitable device for adapting the standard mazda lamp to the lamphouse you use. With these two important factors scientifically and mechanically correct, you will find that mazda light, properly reflected and with complete control in the hands of the projectionist will increase the patronage of your theater, front seats will be just as desirable as rear ones and many new patrons will be added to the roster. It is now very evident that with the use of mazda device for adapting lights to the screen, mazda projection has come to stay. The De Vry Corporation, in its very interesting and new "Manual of Portable Projection," points out some interesting matters in connection with placing the projector in relationship to the screen. We quote: "In professional projection, where every element relating to the desired results when an installation is made, the placing of the projector in relation to the screen, like everything else, is taken into consideration. This is but rarely the case when a portable projector is used, though relatively just as important. Usually the projector is pointed on an upward slant, PHONE BRYANT 3605 UNIQUE SLIDE CO r JU1 Highest Quality Lantern Slides -^ 717 SEVENTH AVE., NEW YORK. with the consequence that the light instead of being reflected back towards the audience is reflected to the ceiling, and consequently lost. "Proportionately, as the size of the picture increases, so does the loss of light, until it is a practical impossibility to get anything like desirable results, and naturally the larger the picture, the more particular you must be in placing the projector in relation to the screen. Even in small pictures too much light is lost to commend this practice. If you must project upward, tilt the top of the screen forward 30 to 40 per cent of the angle at which the projector is tilted. Whenever it is possible to do so, place the projector so that the lens opening in the projector case is opposite the center of the screen. When this is done, the light from the screen will be evenly reflected and a uniformly clear picture will be seen by everyone in the audience, whether seated in front, side or rear of the auditorium. "Where it is impossible to place the projector in a straight line with the screen, place it at as slight an elevation to the center of the screen as possible, pointing downward so that the light is reflected into the faces of the audience. "It is to be remembered that the greater the angle of the downward projection, the greater will be the angle of the reflection from the screen. Too great an angle would result in the majority of the light being reflected into the faces of the audience in the first few rows while those in the rear, close to the projector, would hardly receive any. This, besides producing a distorted picture, resembling an inverted keystone, on the screen. To guard against this — when projection at an acute angle is necessary — tilt the screen back at the top about 30 or 40 per cent of the degree of the angle at which the picture is being projected. A novel way of projecting from which excellent results may generally be expected is to place the projector in an adjoining room and project through the transom or glass door. It has the advantage that the audience is not consciously aware of the source of projection, and is most desirable when a lecture accompanies the projection." * * * Continuing, this interesting little book says about screens: "In portable projection — where showings are given only before small groups at a time — the 6x4-foot screen is the ideal one to carry. An 8-foot screen is the largest size that can be conveniently handled in going in and out of buildings, as the average elevator in a building does not exceed eight feet in height. An 8-foot screen is quite large enough for showings before an audience of a thousand people when necessary but where a permanent installation is made in a room fitted to accommodate five hundred to a thousand people, a 10x9, or 12xl0-foot screen should be used. "Whenever a permanent screen installation is made, under conditions sufficiently favorable as not to require its being rolled up when not in use, by all means have it mounted on a permanent frame and stretched taut." * * * "As is only natural with any article that is approximately five and a half thousandths of an inch thick, which is at the same time fragile, and traveling through a steel mechanism at the rate of a foot or more per second, film is susceptible to a certain amount of wear and disintegration. "Film becomes soiled from particles of emulsion which have loosened, and from dust and dirt accumulated within as well as outside of the projector case. This can, in a measure, be prevented by carefully cleaning the projector after each exhibition. The emulsion side of the film will also, in time, become slightly scratched when the film is put to constant use. When these scratches fill with dirt, streaks very much like "rain" are seen on the screen while the picture is being projected. When this occurs, it is highly advisable that the film be thoroughly cleaned, the best procedure being to return the 'film to the makers. "To remain flexible, film must have a specific amount of moisture. If left in a dry place, it will gradually dry out and become very brittle. In this condition, it frequently breaks. The large exhibitors store their film in vaults, maintaining the necessary degree of moisture. For the non-professional, however, the most satisfactory method of keeping film is to use humidor cans. These will preserve the film in the same way as a humidor box will preserve cigars. They are saturated with a solution made of camphor, glycerine, eucalyptus and menthol, preventing the drying of the film and the rusting of the reel. "It is one of the golden rules of film projection always to preview film with which the user is not familiar. In the course of time many reasons will be found for doing this, as many films contain scenes that are not compatible to the conditions under which they are to be shown." i MJNUSA r COLD FIBRE SCREENS MINUSA MAZDA-LITE SCREENS A special creation for Churches, Schools, Lodges, etc., made in sizes to suit your requirements. Distributors from Coast to Coast Samples and information upon request 1INUSA CINE SCREEN CO. WORLD'S LARGEST PRODUCERS OF r— — -, MOVING PICTURE SCREENS. , IF^SSgcc^l Bomont and Morgan '■ St. Louis, Mo. |[g>iSg531