Moving Picture Age (Nov-Dec 1919)

MOVING PICTURE AGE 29 illlllllllllllllll!!l!llll!lllllllllllllllllllllllllll Projection 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. llllllllllllllll!llllil!ll!ll!l!llll!llll!l]|l!!ll!!lll!!li:!lllllll!IIIIIIIM Phases of Mazda Lamp Projection By H. Freeman Barnes (Edison Lamp Works of General Electric Company, 30 Ampere Mot/on Pictope l/SKP CoNOEHSER AND Mipftoff m Corpect Harrison, N. J.) Three new friends are introduced by three new pieces of necessary apparatus in changing over from arc to Mazda projection. Just as each leg of a photographer's tripod, for example, is necessary in keeping the tripod in a position for usefulness, so each of the three pieces of apparatus with Mazda projection performs its own special and important function in putting the picture on the screen. Most people now understand why it is necessary to employ different apLamp paratus when using the incandescent lamp ; why it is impossible to get proper results by merely substituting the lamp for the arc and making no further changes ; why a mirror is needed and why a new form of condenser must be used. Most people appreciate why Mazda lamp projection has come to stay; understand why a better picture can be projected at a lower cost and with less effort. The fact that most people do not appreciate, however, is that Mazda lamp projection, if results par excellence are to be obtained, requires the initial attention of an experienced man. While in a way, the Mazda lamp is in the long run much simpler and easier to operate than any arc could possibly be, the experienced arc projectionist will find his knowledge of much value in obtaining better results when he changes over to Mazda projection. For those, however, to whom projection in any form is entirely new, the simplicity of the Mazda lamp at once appeals. * * * The most important of the three new elements is naturally the lamp — the source of light. The filament, instead of a straight piece of tungsten wire as in an. ordinary lamp, is wound in a spiral or helix. By coiling the wire, we are able to concentrate the light into a small area. The most convenient way to carry a piece of rope, for example, would be to make it into a coil, to concentrate its area. The wire spring in a common roller window shade if stretched out would be many yards long, but, coiled as it is in the roller, its length is onlv a few feet. The same with the filament. In an ordinary lamp, such as we screw into our lamp socket at home, there has been no attempt to concentrate the light into a small area; but looking at the crater of an arc, we readily see that there we have concentrated light, that in order to be of use the light must come from a relatively small area. A condenser only uses the light coming from or near its focal point and, therefore, the more light _ we can crowd into the small area around this point, the better will the picture be on the screen. Consequently the lamp filament is coiled to concentrate the light. Four little coils are made half an inch long and fastened side by side, enough space being left between them to prevent shorting, and to enable the mirror to function properly. The coils are placed in a glass bulb which is made long and narrow rather than round. A cylindrical or tubular bulb will allow the lamp filament to be placed closer to the condenser. The length of the bulb keeps the blackening (which is bound to take place) above and away from the filament. ♦ ♦ * About the condenser. If we were trying for example, to catch a spreading stream of water from a hose, the closer we placed our pail to the nozzle, the more water we would be likely to_ get. It is just so with a condenser. The closer we can place it to the lamp, the greater will be the amount of light thrown on the film. With an arc, a condenser can rarely be called a friend, since as a rule it cannot be kept in long enough to become acquainted with. Pitted or cracked condensers are only too common. The condenser with Mazda projection may be put as close to the lamp as we wish and still keep it in service. Knowing this and realizing that the closer we can place the condenser (i. e. the shorter its focus is made), a prismatic or a corrugated condenser was developed with a focus of 2l/2 inches (see illustration). It functions in practically the same way as a set of piano condensers, differing only in that the spot on the aperture plate is not as round and even as with the ordinary arc. Since more light is put on the film, however, the appearance of the spot, unless the projectionist has an especially artistic eye, is never a cause for a disturbance. The mirror placed behind the lamp serves still further to Hooverize" the light rays and redirect that part of the light, which would otherwise be lost, back on to the condenser and subsequently on to the film. The mirror is a section of a hollow sphere. It is just as if we had taken a hollow glass ball, silvered Mirror, lamp and condenser dismounted and displayed. Mirror and condenser are turned to show their faces. it so that the silvering was on the inside and cut off a section. When the lamp filament is placed at what would have been the center of the hollow glass ball, the light falling upon the mirrored section is thrown back as an image of the filament, the image falling on or near the filament itself. If we were to call the four fingers of one hand filament coils and the fingers of the other hand the filament images, it would be easily possible to fit them into each other so that a practically solid surface would be obtained. Instead of only four little coils of light, the light source is therefore four eoils and four images which, when properly related, make the light source of almost even brilliancy, and consequently makes the light on the screen practically even. Other size mirrors and condensers have been and can be used than those indicated in the drawing, but experience has shown that the combination specified is the most successful. COLD FIBRE SCREENS MINUSA MAZ-DA-UTE 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 MINUSA CINE SCREEN CO. WORLD'S LARGEST PRODUCERS OF MOVING PICTURE SCREENS. . [gggSgJOT] Bomont and Morgan St. Louis, Mo. |B>>5 sl