The motion picture projectionist (Nov 1929-Oct 1930)

January, 1 930 The Motion Picture Projectionist 27 points of interest with regard to this new A.C. apparatus may be presented: Use Photo Voltaic Cell Raw A.C. current is fed to the filaments of all amplifier tubes. The circuit used is of new and novel design and may be so utilized that the output of the cell may be fed directly into two 250's arranged in push-pull so as to get full theatre volume. Incidentally, a photo voltaic (liquid) cell is used in this apparatus instead of the usual photo electric unit. Full data on this new cell has been given in these pages. Both the exciting lamp rectifier and the "B" battery eliminator are of special design and use special gasfilled rectifying tubes. One type of tube is used for the exciting lamp and another for the "B" eliminator, the combination producing excellent results in eliminating any A.C. hum in the system. Current for the horns is obtained from the use of a dry plate-type rectifier, and no appreciable hum is apparent from the speaker units. Particular interest attaches to the use of the photo voltaic cell, which is radically different from any similar unit now used in sound picture apparatus, and for which a special circuit was designed by Miehling. a cz /r Color Cinematography Recently we presented in this department a general outline of a new and novel system for color cinematography, on which a patent has been granted to K. Martin under U. S. Patent No. 1,728,426, Sept. 17, 1929. We are happy to be able to present at this time specific data on this interesting process which has been gleaned from the patent just granted. Pigs. 1 and 2 show a prismatic arrangement in which one is provided for each complementary color picture. It comprises three rectangular prisms, a, b, c, and each of the two faces of prism b is cemented to one face of each of the other two prisms. The two systems are so disposed that the exposed faces of the prism c are apportioned, respectively, to the two complementary picture d", d' of the film (I in a frame of standard size, and the exposed faces of the prisms c face the objectives e. It will be apparent that with one of the prism systems held in the manner shown in Fig. 2, an arrow placed as shown behind the prisms c would be viewed from the front, through the prism a, in the manner shown. The image would, of course, be rotated through 90°, as a requisite for the purposes of the invention as already explained. In Fig. 3 a source of light is indicated at /, with a condenser g in the path of the beam; a cylindrical dispensing lens h, as shown, or a special condenser system may also be used. If only two color partial pictures f^r._. Figure 3 are to be used, the successive partial pictures d", d' will be taken and projected through red and green filters for example. On the other hand, if four complementary colors are to be used each pair of complementary partial pictures, for example red s~ d green will be followed by a different pair of complementary partial pictures, for example blue and yellow. This arrangement is symbolically indicated in Fig. 5 in which d° indicates a partial picture taken through a red filter, d' a partial picture taken through a green filter, d2 through a yellow filter and cf through a blue filter. In order to uniformly screen the two complementary pictures during the feed of the film a single shutter i of the usual type may be used, covering both pictures. It will be understood that an ordinary projecting apparatus, for black and white work, can be adapted for this purpose, by removing the objective, and perhaps also the condenser system or part of it, and substituting the double objective and prism systems which is described. To change Top, Fig. 1; Bottom, Fig. 2 Figure 5 back to black and white work is equally simple. The color filters p, p' may vith advantage be fixed to the objective holder, m on which are mounted the color objectives e, e, and the objective n for black and white projection, and the change-over can then be made very quickly and easily, particularly if the parts are arranged to slide into and out of position as on the slide r. This is mentioned because it may sometimes be desired to show black-and-white and colored pictures alternately, and films for the former and latter respectively may even be joined together, in one reel. Recording with the Mercury Arc Lamp AT present there are two methods used in commercial recording of sound-on-film, and these are (1) the use of a string galvanometer, such as is used in the RCA Photophone method (saw-tooth), and (2) the use of a gasfilled tube. The first of these methods is very costly, and it is exceedingly difficult to maintain the efficiency of the equipment. The extremely fine wire is often broken by mechanical shock or by a too strong magnetic pull. The use of gas-filled tube is, on the other hand, much cheaper insofar as original cost is concerned, but these tubes also have their limitations in that their life in the recording equipment varies from five minutes to several hours. This short-life period is a result of the deposition of the metal film on the glass wall, making it difficult for light to pass through the metal film on the glass tube. Another undesirable feature of these tubes is that they generate very little actinic light, which means that the film is considerably underexposed, photographically speaking. To compensate for this latter defect a contrasty sound track print is made. Rich in Actinic Light It is known that the mercury arc lamp is extremely rich in actinic light and therefore should make an ideal means for recording. Several experimenters attempted to use the mercury arc as a light source for sound recording, but the results of all of these efforts were of no commercial value. P. M. G. Toulon, an "old hand" with