International photographer (Jan-Dec 1934)

September, 1^.:4 T 1 1 I X T E R N A T I ( ) X A I. I' H 0 T OCR A I' II E R Twenty-one that it is a faithful copy of the sound waves that we wish to record. We must also assume that in addition to the speech circuit that brings in this speech current there are the necessary battery and power circuits entering the recording room. The Film Recording Machine The machine in which the motion picture film is exposed to this varying light beam is known as the film recording machine; and it is comparable to the motion picture camera, in which other film is exposed to the light reflected from a scene that is being photographed. Both the film recording machine in the recording room and the motion picture camera on the sound stage are driven by special "interlocking" electric motors that start to revolve and stop at exactly the same time and that run at precisely the same speed. The speed of these motors is regulated so that they never vary by more than one-tenth of one per cent from a fixed speed of exactly 1200 r.p.m. when they are running. The use of interlocked motors makes it possible to place start marks on the film in both the camera and the recording machine, and then to print the two pieces of film together on one positive film after they have been exposed with the assurance that they will match perfectly. Because the two start marks are made at identical points on the pieces of film in both machines and the machines started and run at precisely the same speed, the picture and sound track on the two pieces of film naturally must coincide exactly. Another point of similarity in the camera and recording machine is in the light-tight construction of the box in which the film is exposed to light shining through a lens system in one end. However, the two machines differ in that the film moves uniformly and continuously past the lens system in the recording machine, whereas in the camera the film is drawn down intermittently a frame at a time past the one lens. The same type of film magazine is generally employed now on both types of machine ; and the machines are both equipped with footage counters that indicate the number of feet of film run through the machine. Film Recording Machine Construction The mechanical construction of a film recording machine is evident from the accompanying photograph. The rectangular metal box is the chamber in which the film is exposed; and the two drum-shaped containers are the magazines in which the film is held before and after exposure. The film travels down from the loaded magazine on the top of the chamber through the recording chamber and on into the lower magazine. On the end of the exposure chamber opposite the driving motor is the lens system and the light valve as sembly. Farther out on this same end of the machine is the lamp house in which is mounted the electric lamp that furnishes the light of constant intensity. The footage indicators are the two knob and pointer arrangements on the front of the exposure chamber. The whole recording machine and motor assembly is built on a special concrete foundation. Just beneath the center of the machine is suspended a square metal box carrying the PEC amplifier (PEC represents photo-electric cell, a light sensitive vacuum tube), the functioning of which will be discussed in succeeding chapters. The large panel on the wall back of each recording machine is the control board on which are mounted the battery and speech circuit controls, the meters, and the other equipment associated with the recording machine. The large control knob on the box mounted beneath the meter on the left-hand wall in the photograph functions as a control element in the motor circuit, as will be described in a later chapter. The meter likewise is in the motor circuit. It serves to indicate when normal recording motor speed has been attained. The row of switches in the metal box on the extreme left is the starting and stopping control for the motor system. There are usually two film recording machines attached to each recording channel. The film magazines are removable to permit loading and unloading the film ; and the door on the front of the exposure chamber is easily opened to allow the threading of the machine and the punching of the film with the start mark. The upper magazine from which the film is drawn is known as the feed magazine and the other one is termed the take-up magazine. Uniform Film Motion Necessary It is necessary that the angular velocity with which the film is carried past the lens system that focuses the image of the light valve onto the film be as uniform as it is physically possible to make it. In the recording machine there are two large wheels around which the film is carried inside of the exposure chamber. These wheels are known as the sprockets; and it is while passing over the sprocket just in front of the lens in the exposure chamber that the film is exposed to the light passing through the light valve. This sprocket engages just twenty of the sprocket holes in the edge of the film; so there is almost no possibility that the film will slip while passing under the light beam. These sprockets are both driven by the motor shaft through a worm and worm-wheel; but whereas the upper of the large sprockets, the one that draws the film from the upper magazine, is driven directly by the (Turn to Page 24) EXTENDED MIXING PANEL With Intercommunicating Telephone System and Volume Indicator for "ArtReeves" PORTABLE SOUND EQUIPMENT DEPENDABLE LABORATORY AND SOUND EQUIPMENT Francais Deutsch Espanol Svenska Hollywood Motion PicTure/cquipmemT (p |Td 645 NORTH MARTEL AVE CABLE ADDRESS ARTREEVES Phone: WYoming 4501 HOLLYWOOD, CALIFORNIA, USA Please mention The International Photographer when corresponding with advertisers.