The motion picture projectionist (Nov 1929-Oct 1930)

January, 1 930 The Motion Picture Projectionist 43 Sound reproduction is a carefully developed science and variations from perfection seldom come from any reasons except human carelessness. When a sound picture leaves the studio, it is as perfect an example of fine recording as the skill and care of the production personnel can make it: if it is properly cared for and carefully projected it should also give perfect reproduction. — American Cinematographer. Ed. Note: — The foregoing, with the exception of the last paragraph, is very constructive work, indeed, yet the paragraph in question gives rise to the thought that, in the interests of consistency, it might not be a bad idea for a projectionist now to turn about and prepare a list of those faults which are quite common in recording technique. This listing could be concluded with the admonition (to engineers) , that with projection technique so far advanced, flawless recording would positively result in a perfect picture on all theatre screens. Troubles and Maintenance (Continued from page 16) phonetics, and once the installation is functioning properly, no trouble will be experienced. If it is not properly designed, the engineer making the installation will demonstrate sufficiently to give you a thorough training in this portion of design. Crackling may be caused by the following:— loose connections somewhere in the exciting lamp circuit, indicated either by a nicker in the exciting lamp or in the ammeter in this circuit; loose connections in the photo electric cell circuit or in the amplifier battery connections. In "shooting" this trouble, start at the beginning. Turn off the exciter lamp. If the crackling ceases, the trouble is there. If the crackling continues, remove the photo electric cell, the cell leak, and the first tube, and continue until the trouble disappears. As soon as the noise ceases, the trouble may definitely be located between the last two elements. Bad leaks in the coupling circuit of the cell will cause crackling. Remove the defective leak and replace with one of the same value. Use metallic leaks. The rheostat in the exciting lamp circuit is a particularly bothersome element in this respect. Oilsoaked wiring will sometimes cause this trouble. Freshly charged batteries will cause this condition until the gas has leaked off the plates. Remember that a loose fuse in the battery room may affect a circuit just as much as if it was located on the projector itself. When you inspect a circuit, do it thoroughly and then only one circuit at a time. Optical systems have been discussed in detail, and in excellent fashion, by Samuel Wein in these columns, thus we shall discuss only the maintenance aspects of this unit. The majority of optical systems are so designed that the lens assembly can be removed for Ask the Projectionist Who Uses Them / *$ xP **S V% «?* *G J~ ¥*> ^ STRONG Automatic Reflector ARC LAMPS 5> S> ^ "^ For Sale by Trustworthy Independent Supply Dealers Everywhere Export Office — 44 Whitehall St., New York City, New York 1 i>e Strong Electric c< 250I Lagrange St. Toledo, O. cleaning without the necessity of realignment. For the benefit of those who have systems that are not so designed, we will give the method commonly employed to obtain correct adjustment. Clean the optical system thoroughly using a piece of lens cloth and replace the lens in the mounting in approximately the same position it was in when removed, so that the slit will be at right angles to the edge of the film. Most lenses have a line or some other designation to show the edge of the slit wit^ reference to the outside of the barrel. Place the exciter lamp in position and adjust for maximum light at the window where the photo electric cell is normally placed, using a piece of film or the waxed wrapper from the outside of a package of cigarettes to cover the window and act as a screen. Clamp a piece of black film in the film gate and adjust by means of moving the lens toward or away from the gate until the line appearing on the film is sharply in focus to the emulsion side. Remove the film and replace the paper in the photo electric cell window and adjust the exciter lamp until a clear field and maximum illumination is obtained. Be sure that the light beam is at right angles to the edge of the film by catching the beam on the edge of a frame with the film in its true running position. (To be continued)