British Kinematography (1952)

108 BRITISH KINEMATOGRAPHY Vol. 20, No. 4 a distinctive range of equipment is becoming available. In this country interest in the new technique is growing rapidly and it would have been more advanced if the unsettled condition of the industry had shown some improvement during the last year or so. Conversion of Equipment The first equipments have been in use since about August of last year and consist of conversions of the standard RCA photographic channels. The conversions are for the present all applicable to the model Fig. 2. LMI.903I reproducer head for magnetic and photographic track, showing (I) optical assembly for photographic track, (2) magnetic play-back head, and (3) retractable carriage. PR.23 recorder (Fig. 1) and 9031 series soundhead (Fig. 2) whether used as a film phonograph or in combination with a picture projector. After conversion, the assemblies become dual purpose and retain all the features and performance for photographic recording as originally designed. The conversion features are oi some interest and as far as possible, without making a Christmas tree of the machine, attempt to include all the essential functions required by production personnel. It will be recalled that in the past all RCA film movements for both recording and reproduction embodied a soft loop film path, whereby in the recorder the film at the time of passing the exposure point was isolated from mechanical disturbance due to sprocket wheels and the associated drive members and any irregularity caused by engagement of the film over the sprocket teeth. Such a method of film traction is not at all suitable for magnetic recording as now the recording and monitoring heads must be in close contact with the active surface of the magnetic film. The first change therefore, is a remodelling of the film path so that additional plain and loaded rollers are introduced before and after the recording drum. The geometry of the new path may be clearly seen in Fig. 3. Off Drum Recording and Scanning In revising the film path to a tight loop arrangement, a square housing was introduced to provide additional space for the various units. This new film path gives a satisfactory film movement and has proven as good and stable as the soft loop when recording on either photographic or magnetic film. Two magnetic heads are mounted in the bottom part of the housing on a retractable carriage. Looking at the machine from the operating side the recording head is on the left and the monitor head on the right. The recording head is mounted so that its gap shall be as close to the outgoing side of the recording drum as possible. In this position excellent performance is achieved and of course there is flexibility in meeting any track position standard. This method of mounting is commonly termed " off drum recording and scanning." The alternative mounting, used in some of our equipments whereby the head is placed in the recording drum, is called " inside drum recording and scanning." Flutter Readings In general, RCA prefer the off drum scan position because of the greater flexibility available. The overall flutter readings for this recorder movement using off drum