Journal of the Society of Motion Picture and Television Engineers (1950-1954)

into a sequential picture, which might ease some of the recording problems. The principal objection to the method is the additional complexity and the distinct possibility of loss of quality in the conversion process. (3.2.5} American Method: Although this is not applicable to British standards, since only 24 of the 30 television pictures/sec used in America6 are recorded, it is interesting to compare the exposure cycle with those of the British methods described in Sec. 3.2.7 and 3.2.8, which are suitable for 25-pictures/sec television recorded at 25 film frames/sec. Figure 5 (a) shows the American television waveform diagrammatically, while Fig. 5(b) shows the shutter sequence at present used in America. It will be seen that every alternate field is joined in the picture area. With the relative phasing of camera and television signals as shown, this join occurs in the centre of the picture ; with other conditions of phasing, a join in the picture area occurs on each field. Picture joins are dealt with in Sec. 4.1. (3.2.6) Alternative Exposure Sequence for American Standards: This uses a double optical system and double-gate aperture, the images being one above the other. The shutter sequence is shown in Fig. 5(c), and a schematic of the camera in Fig. 4. Television picture 1 is recorded in the bottom aperture, then television picture 2 in the top aperture. One field of television picture 3 is then missed while the film is advanced two frames and the cycle is repeated. The advantage of this arrangement is that there is no picture join. The method is of particular interest, since the camera developed to record British standards on the Kemp-Duddington system could be adapted to record American standards on the above sequence. A pull-down period of 72° would be required, compared with the 90° on British standards, but it is felt that this could be achieved without radical modification. (3.2.7} 76% Method*: This uses the time of every third scan for pull-down, thus providing 16f film frames for every 25 television pictures. A step printing operation to print every other film frame twice is required to obtain 25 frames/sec on the film. The reproduction of movement is, of course, not so good as in a 25-frames/sec method but should not be worse than that associated with the step printing of 1 6-frames/sec motion pictures to 24 frames/sec. The exposure sequence is shown in Fig. 5(e), Fig. 5(d) being the B.B.C. television waveform. (3.2.8) Kemp-Duddington Method6: This is the system which the B.B.C decided to develop for 16mm recording.9 A double optical system and two-frame pull-down is required. The exposure sequence is shown in Fig. 5(f), and the camera schematic is the same as that of Fig. 4. The first and second scans of television picture 1 are recorded by image 1 in the bottom aperture, and the second scan of picture 1, together with the first scan of picture 2, is recorded on the second film frame in the top aperture. The second scan of television picture 2 is not recorded, the film being advanced by two film frames in this period. The cycle is then repeated. With the phasing shown, no picture join is necessary. To ensure that the correct phasing is maintained, the camera is phase-locked to the television-frame pulses and the relative phase angle is indicated by stroboscopic means. It will be seen that some 90° of the cycle are available for film pull-down, and in the design of the camera an accelerated triangular cam-movement was used giving a pull-down of 60°, with 15° allowed for registration. This was done by means of register pins fixed to the aperture plate. Optical registration of the images is necessary, and means are provided for W. D. Kemp: Television Recording — Abstract 373