The Cine Technician (1935-1937)

88 The Journal of the Association of CineTechnicians Dec, 1936-jan., 1937 All the improvements made have contributed to a steady raising of the quality standard, but the essential extension of the recorded frequency range has presented problems which can only be successfully overcome by developing a means of providing a much more well-defined negative and print. The Figu (a) ol the Velocity actuiited pail ol Ihe ribbon combines with the ciiculai pallein (b) of Ihe pressuie-actuated half to provide an ovc;all pattern (c] which takes lh« form oi a catdiod -lOQ -no -lie -tie ~ " ^ ' "^ , _i _ 5t.78S|0' »W 4 ^6 7a,|0' -i 3 FREQUENCY FtG 4 '^eoreticu^ll;^ predicted .a^^d experimentdj response df unidirectional microphone at 0 degree (zerodb = Ivolt). Note Data show open-cii^uiC voltage of ribt>on The recent sudden extension of the frequency range placed a burden on film laboratories by requiring them to develop and print to very close tolerances in order to avoid the low frequency modulations, which ruin quality, when distortions are introduced into the upper frequency range. Two of the serious causes of distortion which are sometimes very prevalent are poor contact at the exposure point and printer slippage, the latter being due to the uneven length of the negative film and printing stock. Heretofore, in printer apparatus correction has been allowed for a definite amount of negative shrinkage, but in practice the varying conditions met with in film processing prove that a wide tolerance of correction is needed to accommodate the varying amounts of negative shrinkage experienced. In Figure 7 is illustrated the difference which can occur between two prints obtained from the same negative. One can well realise that the audible results from Figure 7b, when played on a modern reproducer having a wide range of response and cushioned rotary stabiliser would give appreciable distortion and such a print' if used for re-recording where the defect would become additive would become impossible. Distortions as outlined may now be eliminated by the use of the non-slip printer and a photograph of the first experimental model is shewn in Figure 8. It is interesting to note in passing that this model was sent to Hollywood from Camden for test purposes and results were such that many thousand feet of commercial prints have been handled for different studios with a marked improvement in sound quality. The principle employed on the basis of which the printer described was designed is as follows : — Two belts differing in length may be made to travel past a given point without shppage between the two, provided the belts are held in contact around rollers in such a way to prevent slippage along the line of contact. This statement is based on the fact that when bending a belt round a pulley or roller, the mean length of the belt remains always the same, while the concave side is compressed and the convex side stretched in proportion to the curvature of the roller. If the belt of shrunken negative is bent around a roller of the proper diameter, the outer surface will become longer than the mean length of the film. Thus, if the longer unshrunken raw stock is passed over the same roller, assuming good contact, the concave surface or compressed side of the long raw stock will make contact with the stretched side of the short negative only along the line of tangency. From Figure 8 it can be seen that the film path has been so arranged to allow a loop to form before the printing point is reached. Any small variation in film loop will cause a corresponding large change in the angle at which the film approaches the contact point. The printer, as designed, will correct for negative shrinkages from 0 to | per cent. The film must not pull taut o\-er the pressure roller and the amount of compensation with the size roller provided will correct until tlie difference between the Figr. 5. FIGURE 6 —SCHEMATIC WIRING DIAGRAM OF THE MODEL P8I32AI NEON VOLUME INDICATOR. lengths of the two films becomes so great that the diameter of the roller is too small to allow fle.xing the film round it. A rotary stabiHser is attached to the printing drum shaft to provide satisfactory motion at the printing point while the pad roller ensures proper contact at the printing point. It is important that the printing light strikes the film at the contact point only, to prevent blurring of the image, and arrangements have been made to restrict the height of the light to about 0-0025". This is performed by imaging a 0'005" mechanical sht on tlie film through a two-to-one reduction. As a clearer indication of what the printer is, we have been able to advance production sufficiently in London to place a production unit before you to-night. It is quite anticipated that the introduction of this printer will eliminate the cause of distortions in printing work and