Projection engineering (Sept 1929-Nov 1930)

Page 10 Projection Engineering, June, 1930 A Sound Printing Attachment for the Model D Continuous Printer Absolute Film Registration Provided. Sound Negative Printed Independently of Picture Record IN order to fulfill the technical and commercial exigencies imposed upon the motion picture laboratories by the advent of sound pictures, it was found necessary to devise means by which the accurate and rapid printing of the sound negative could be conducted independently from that of the picture record. The well-known characteristics of sound recording and reproducing demand an extremely smooth and continuous motion of the film in front of the scanning slit, as well as a perfect control of the sources of light which impress the film upon which the sound record is registered, or excite the photoelectric cell in the process of reproduction. The meticulous care with which a film sound record is made would be of no avail if the printing process of the sound negative could not be controlled with equal certainty and accuracy. From the early inception of sound pictures, it was evident that the continuous printer, model D, answered all the requisites of sound pictures, because through years of patient re * The Bell and Howell Company. By Joseph A. Dubray* search it had reached such point of development that all the refinements most appropriate to take care of absolute film registration were incorporated in it. It remained to devise means by which the printer could rapidly and with the least inconvenience to both Fig. 1. Triple adjustment sound attachment installed in continuous printer. Fig. 2. Manner in which sound attachment is arranged. laboratories and producers be made adaptable to the new condition. The Bell & Howell engineers happily solved the problem by designing a triple adjustment sound printing attachment which can be adapted to all of the company's printing machines in existence, and, of course, to all apparatus being manufactured. In order to fully appreciate the problems involved and the unique manner in which they were solved, we may summarize the requirements imposed. 1. It was desirable that existing equipment could be used. 2. The sound attachment should preferably require only nominal alteration and fitting. 3. Definite light control for printing the sound and picture portions independently should be insured. 4. If possible, the attachment should permit printing either the sound or the picture area from either end of the roll, to eliminate waste time in rewinding. 5. It was desirable that it comply with the standards approved by the Society of Motion Picture Engineers, whereby a black light shield is to be printed along the sound track to eliminate any possibility of variation of tone in sound reproduction due to a possible side motion of the film in front of the scanning slit of the projection apparatus. 6. The device should be convenient ; quickly set at any desired adjustment, positive and accurate. 7. It was desirable to have the masks arranged so that the full negative (for silent pictures) could be printed at one adjustment. The following description will explain clearly how very effectively we have solved this problem, and the figures illustrating this article will clearly illustrate the working of the attachment. In Figs. 1 and 2 the triple adjustment sound attachment is shown installed in the continuous printer. The attachment itself consists of two main assemblies : the masking unit and the operating lever unit. The masking unit is installed in place of the usual top aperture plate. After it has been accurately adjusted in the printer, a hole is drilled through the top of the printer casting into the L ' ^ lf^_ jLA-j <n »J x*^ PJo. ZjL -*•* A mfm b d IV Fig. 3. The complete unit. masking unit, and tapped. This insures the masking unit always being held in perfect alignment. The operating lever unit is then inserted through an accurately milled slot in the printer casting so that the levers engage the masks proper. The operating unit is then fastened permanently in position. In Figure 2 is plainly shown the manner in which the sound attachment is arranged. Note carefully how the masks of the sound attachment interlock with the lower aperture jaw to prevent light leakage. In the early models of the printer, the printing light was controlled through the mobility of the jaws of the