Movie Makers (Jan-Dec 1952)

207 I k ,i>.v' *' FIG. 3: Start-mark system recommended by Revere involves matching prepared cue spots. A punch hole in film is starting signal. FIG. 4: A handy metal mirror, supplied by Revere with SynchroTape kit, assures deflection of adequate light on moving tape. Revere's Synchro-Tape, a unique magnetic medium with a built-in stroboscope, blows the whistle on tape shrinking, stretching, and slipping to variations in projection speed. But all too often a disappointed projectionist would still find his carefully controlled show out of sync. Somewhere in the system there were still other sources of error. It was these difficulties, already known to many, which Mr. Levett clearly cited when he wrote in January Movie Makers as follows: "The only possible source of error in this system — and I believe it to be a minor one — is the question of shrinkage or stretching of the tape, and of slippage as the tape passes the capstan." SYNCHRO-TAPE FORECAST And, as clearly, it was the principle now embodied in the Revere Synchro-Tape which Mr. Levett forecast when he concluded: "However, a (control) system which is just as effective as the Maurer method (a visual sync-pulse setup) is to mark the tape. In this case, a small white dot, or a white vertical line, is printed on the tape every inch or so throughout its length, the distance between the points being predetermined for the frame speed desired and the rate of tape travel." Mr. Levett then pointed out that these dots or stripes (which are simply another form of strobe pattern) being directly on the tape itself, will reveal under scanning by the projector light any effect on synchrony created by the stretching, shrinkage or slippage of the tape. Thus, we see that these three possible sources of error — tape stretching, shrinking, or slipping as it passes the capstan — are the difficulties which Revere's Synchro-Tape system now does away with. Since the tape's linear strobe pattern also will reveal variations in projector speed, the amateur scoring his films with magnetic tape will clearly appreciate the vital importance of this new product. SYNCHRO-TAPE IN USE In operation, this strobe-patterned tape is set up in exactly the same manner as was the regular tape used by Mr. Dow. As diagramed in Fig. 2 and pictured in Fig. 3, the recorder is positioned directly in front of the projector and slightly below its light path. To assure that adequate light falls on the moving pattern, a small metal mirror (supplied by Revere with each reel of tape) is spring-clipped to the projector's lens barrel as is shown in Fig. 4. This deflector does not obscure the screen picture in any way, since it is too close to the lens to create a shadow image. As a synchronized start-mark system, Revere recommends the following procedure; punch a round hole in the opening strip of black leader (see Fig. 2) ; affix a strip of marking tape at a suitable point on the recorder's chassis (see Fig. 3) ; place another strip of marking tape on the Synchro-Tape itself and in threading up align this with the start mark (again Fig. 3) ; start the projector and, when the punched hole flashes white on the screen, then start the recorder. During projection, if the linear strobe pattern seems to creep, adjust the projector speed to compensate. . . . There are, of course, other start-mark systems, and each amateur will adopt the one best suited to his operating procedures. WIDESPREAD APPLICATION According to Revere, their Synchro-Tape system can be used successfully in conjunction with any silent projector having a three-bladed shutter. This is indeed true. But, as a safeguard, we add the minor qualification that any such projector must also operate under an adjustable speed control. Since practically all silent projectors today meet both of these qualifications, the potential use of the Synchro-Tape system seems unlimited. However, Revere also states that the Synchro-Tape pattern is designed for successful use only with recorders operating at the 3% inch-per-second speed. This, we believe, is a good deal short of the whole truth and sets a needless limitation on the possible use of this effective new medium. According to our arithmetic, the Revere SynchroTape pattern as-is can be used on recorders operating at 3%, 7Yz ar|d 15 inch-per-second speeds. Here's why . . . THE STROBOSCOPE FORMULA The relationships between projector speed (frames per second), rate of tape travel (inches per second) and a given stroboscopic pattern are expressed by the following formula: R x N equals F x S when R is the rate of tape travel; N is the number of strobe segments, or in this case the number of lines (15) per inch on the Synchro-Tape; F is the frames-per-second projection speed, and S is the [Continued on page 216]