International projectionist (Jan 1959-Dec 1960)

between the guide rails just sufficient to clear new unshrunken film will fail to edge-guide seasoned prints, but may sometimes cause them to "bounce" sharply from side to side. This distressing effect is often so evident in CinemaScope showings that one can almost guess what make and model of projector is being used! Set these rails as far apart as they will go, or, still better, discard them if possible. 2. The condition of the gate film runners has a tremendous effect upon focus and film buckling. Even though made of hardened steel, the film runners gradually lose their flatness by becoming hollowed out at those points where the friction of the film exerts the most wear. A hollow only a few thousandths of an inch in depth may buckle the film out of shape enough to throw one corner or one side of the picture (usually the right-hand side on the screen) perceptibly out of focus. Using a short steel straight edge and a small flashlight, check the flatness of your film runners before blaming the lens for that fuzzy upper or lower right-hand corner of the picture! 3. The tension of the gate-door pressure pads is important to the rocksteadiness of the picture. Replace worn pads (which wear hollows in the film runners) and test their tension before blaming the intermittent movement for a jiggly, fluttery picture! Remove the gate door from the machine and thoroughly clean the pads before adjusting their pressure. Accumulations of film dust and linty dirt are often found lodged behind them. Then press upon the pads with a finger to find out if the pressure is the same on both sides — it should be, as you know. The writer personally believes that the set of pads directly over the aperture should exert a somewhat greater pressure on the film than the upper set of pads. In other words, if you are using a total of 10 ounces of pressure, the lower set of pads should exert about 6 ounces, and the upper set 4. Notes on Gate Tension To obtain an accurate estimate of total gate tension, attach a spring scale (the kind used by rag buyers) to a foot length of clean black-and-white film. Remove the upper magazine and fire-roller box, place the film in the gate (clearing the intermittent sprocket), and pull it slowly upward through the gate by means of the at Tape Recording, Reproduction T^HERE exist in the minds of those who do not work with the medium numerous misconceptions as to the manner in which magnetic tape is recorded and reproduced. Here are the basic facts as to the "how" and "why" of the process. Every picture is made up of lights and shades, that is, areas of high and low brightness. In television the> scene is "scanned," meaning that narrow horizontal lines across the picture are systematically examined from left to right. At each point of the line the brightness of the picture is determined. The signal obtained by scanning a line is therefore nothing more than a record of the brightness across the line. And if the lines of the entire picture are scanned or examined one after another from top to bottom, the resulting signals are a record of the entire picture. It is these signals which must be permanently recorded and then played back to reproduce the original picture on a TV receiver. Record One of Varying Magnetization For magnetic tape recording, a TV camera is used to get these brightness signals from the original scene. Then the signals are recorded on moving magnetic tape. As is well known, tape records are nothing more than lines of changing magnetization of the tape, that is, the recording head creates very tiny magnets in the tape material. The strength of these magnets is the record of the corresponding brightness of the picture lines. Then the reproducing head, passing along these same lines, has voltage and currents induced in it by the tiny magnets on the tape, and these currents are again related to the original brightnesses (or "video" signals). Thus a videotape record is a record in the form of tiny magnets created in lines on the tape. These magnets, then, represent the brightnesses of the picture, and from them it is possible to recreate the original brightness signals and thus to produce again the original television picture picked up by the TV camera. Note, therefore, that for videotape recording one must have a TV camera (for pickup and recording) and a TV receiver and picture tube (for display of the picture). In addition, the tape recorder must be provided with a magnetic recording head to make the record, and also a tape reproducing head to "read" the tape record. In a way, this resembles sound or audio-tape recording except that picture brightness instead of sound intensity is recorded. tached spring scale. The scale will then register the gate pressure, which should be between 6 and 18 ounces for the best results and minimum film wear. The highest allowable pressure (1518 oz.) need be used only in theatres showing mostly old, well-seasoned prints. The lowest feasible pressure (6-7 oz.) is to minimize "sticking" of freshly processed "green" film. An average pressure of 10 ounces (9-11 oz.) is best for the large majority of theatres. The newer projectors have simplified pad-pressure controls which permit the pressure to be varied during projection. Readjustment of pad pressure is somewhat troublesome on the older projectors, but well worth the time taken to accomplish it. Observe the following precautions, however. (1) Have a few extra leaf-type pad tension springs on hand to avoid an emergency in case of accidental breakage. (2) Have the same tension on both sides of the gate. (3) Avoid excessive tension which wears both the film perforations and the teeth of the intermittent sprocket. 4. The aperture, itself, affects only the optical "framing" of the picture, and has no effect upon the film or its movement through the gate. We may therefore pass over this item for the present with the reminder to keep all aperture plates clean and free from dirt which shows up on the screen I Continued on page 22 ! INTERNATIONAL PROJECTIONIST • SEPTEMBER 1959