International photographer (Feb-Dec 1929)

Fourteen The INTERNATIONAL PHOTOGRAPHER June, 1929 £ikncing the 'Bel/ & UTowell BY A. S. HOWELL and J. A. DUBRAY [This paper, under the title, "The Motion Picture Camera and Sound Pictures," was read by Joseph A. Dubray at the Spring Contention of the S .M. P. E. held in New York City, May 1929, and has become a part of the S. M. P. E. Transactions. It has to do with the silencing of the Bell & Howell for use in photographing sound pictures and will be found interesting and timely by users of this camera. — Editor's Note.] PART ONE SILENCING THE MOTION PICTURE CAMERA The necessity of eliminating all extraneous noises in sound recording Cinematographic work is self evident and too well known to warrant the entering into any discussion on it. It is also well known that the elimination of such disturbing noises is of much greater importance when scenes are taken within the studio stage than when the work is conducted in outdoor locations. Previous to the advent of sound pictures, the motion picture camera was devised and constructed with a reasonable disregard of the mechanical noises produced by the rather complicated operation of the instrument. With the advent of Sound Pictures, these noises have relegated the Cinematographer and his apparatus to a sound-proof booth imposing upon him a number of serious limitations which conflict with the freedom of action necessary for obtaining the fine photographic results which have characterized modern motion pictures productions. The necessity of eliminating the camera noises was immediately apparent to all interested in the new Art and engaged the immediate attention of camera manufacturers and of the Engineers responsible for the developments of the instrument. The rapid but extremely careful and dispassionate examination, brought forth the necessity of departing from some principles of construction which were considered fundamental to the good functioning of the motion picture camera. On the other hand, sound synchronized pictures eliminated the possibility of "cranking" the camera by hand and the introduction of a motor drive permitted the mechanical engineers to attack the problems inherent in the silencing of the apparatus with an entirely new conception of the heretofore considered essential attribute of smoothness of running. This new condition permitted the substitution of all ball bearings existing in the camera for solid bronze and hardened steel bearings so adjusted that all clearances and tolerances were reduced to a minimum. The lubrication of the solid bearings presented new problems insofar as the apparatus is called to perform under unusually trying conditions. Provision has been made inorder to render these parts readily accessible at any time and although it is true that the lubricating of the silenced camera demands more attention and greater constancy than the regular camera, it can be performed with perfect ease and only demands a normal amount of care. The noises particular to the enmeshing of metal gears have been eliminated by alternating them with formica gears. The gears connecting the main drive shaft and the intermittent mechanism have been cut spirally so that three teeth are constantly enmeshed, thus giving assurance of perfect smoothness in running. An extremely interesting problem was brought forth by the necessity of eliminating the noises proceeding from the rewinding of the film in the take-up section of the magazines. The take-up of film was happily solved from the early days of Cinematography by the use of a spring belt connecting the drive movement of the camera with the takeup pulley of the magazine. This belt was kept sufficiently loose so as to avoid an excessive tension, and sufficiently taut to assm*e an easy winding of the film. The spring belt would slide and skip over the magazine pulley, whenever the speed of the latter was reduced by the increase in size of the roll of film being rewound in the magazine. For a number of years this arrangement gave perfectly satisfactory results and the noises produced by the skipping of the belt as well as those produced by the joint of the belt when hitting the take-up pulley, were considered as unavoidable and of very little consequence. These take-up noises were to be completely eliminated and after much study and experimentation, an endless fabric belt together with a new belt-tension equalizing attachment, which automatically secured the proper tension and uniform take-up of the exposed film in the magazine, were adopted. Figure 1 shows this arrangement and its adaptation to either a magazine having a capacity of 1000 or to one holding 400 feet. The investigation conducted by the Bell & Howell Engineers, proved that the film magazines themselves were responsible for the transmitting and accentuating of noises or vibrations produced by the camera mechanism, the elimination of which was essential. The drumming effect which was due to the shape and hollowness of the magazines, was eliminated by drilling their back and cover with numerous holes in spiral formation and by covering them with a one quarter of an inch thick layer of spongy rubber. Figure 2 shows the position of the holes in the back of the magazine from which the felt lining has been removed and of those in the cover from which the rubber covering has also been removed. The spiral formation has been adopted after conclusive experimentation proved that the vibrations of the camera mechanism were completely interrupted by these orifices so disposed, at the moment they reached the large surfaces of the magazine. These surfaces acted, previous to their alteration, in a manner similar to that of a vibrating diaphragm. The magazines have also been equipped with especially designed rollers and hubs with oilless solid bearings which are made with painstaking care and accuracy and which are absolutely free from the noises previously inherent in these units. To further insure the suppression and dampening of any residual noises, the interior of the camera and the shutter blades have been lined with a sound absorbing felt. Figure 3 shows two views of the camera, one with the lens turret and front plate removed, showing the main formica gear and shutter and the other with the camera door open to show the intermittent movement and the felt linings in the camera door. Improvements brought about in this movement, consisted mainly in the substitution of formica for steel gears, in the setting of the film tension at from 1 V2 to 2 ounces, and in the elimination of four out of six driving fingers eliminating the noise formerly produced by the pawls clearing the film perforations as they passed back for a new hold on the film. Figure 4 shows at "A" the film gate open, and at "B" the closed mechanism with cap removed, disclosing the formica gear and the anti-reverse locking spring. Through these alterations it has been possible for the Engineers of the Bell & Howell Company, to contribute to the advance of sound and talking pictures by evolving a camera suitable for work on the sound stage and which has proven, through actual demonstrations conducted in the course of production, that it can be safely set and operated, without the protection of a booth, as close as from eight to ten feet from the microphone without any of its noises resulting detrimental to the recording of sound and voice. (Continued on Page 20)