Motion Picture News (May-June 1921)

May 2iS , I 9 2 I The Bell and Howell UltraSpeed Device for Slow Motion Work By C. E. Marshall SCIENTIFIC and experimental research efforts during the last half decade have resulted in greater strides toward perfection in film bases and emulsions for high-speed photography than was evidenced in mechanical developments up to the present date for the fullest utilization of the extreme speed put in the emulsion by the chemist. In theory, exposures at 128 per second are as easily obtained as 16 per second, however, until some form of continuous movement camera is devised that will supersede the present intermittent. The laws of inertia of moving objects and the low tensile strength of film base will constitute the most obstinate obstacles to overcome in the negotiation of ultraspeed photography on a practical basis. In order to make 128 individual exposures per second with present types of film cameras which will not permit of light being admitted to the film longer than l/272nd of a second, at this speed the mechanism from which the film derives its movement is required to travel through a perpendicular path and completely reverse its direction of travel 256 times per second. This means that the film must be accelerated from the stationary period to a speed of approximately 16 feet per second during its travel downward for the succeeding exposure and then brought to the stationary period again, consuming but l/242nd of a second to complete this entire cycle of events. It is thus quite obvious that the ordinary shuttle or claw movement, whose weight and construction is adjusted for a speed of 16 exposures per second, would be entirely unsafe when functioning at 128 exposures or more per second. Owing to the extreme rapidity of the oscillations of the moving element, the weight and mass must be kept as low as possible in order to minimize wear and undue vibration. This requires a film movement mechanism differing entirely from the conventional type, but built to efficiently perform the same duty. The shuttle of the regular Bell & Howell Cam and Shuttle Movement weighs approximately one ounce and is constructed as light as is consistent with regard to the duties imposed upon it. In the Bell & Howell Ultra-Speed Shuttle Movement the shuttle or vane is constructed of high-grade steel carefully tempered and accurately ground to size; the reciprocating element of which weighs but 70 grains or .166 ounce. By keeping the total weight of this reciprocating member at the low figure mentioned the inertia at the instant of the reversal of direction of travel is within limits that insure the same reasonable length of life that could be expected from the regular shuttle movement operating at 16 exposures per second. Aside from the qualities mentioned in the foregoing paragraph actual operating tests have proven the noise emitted by the ultra-speed movement to be less than that of the regular movements due to the finer state of equilibrium obtained between the moving parts as a result of their greatly reduced weight. The Bell & Howell Ultra-Speed device consists of two separate and distinct units, one of which attaches in place on the exterior of the camera and increases the ratio of gearing between the operating crank and the normal crank shaft, thus effecting a shutter shaft speed of 128 revolutions per second with normal turning speed of the crank of two turns per second. The other unit, comprising the ultra-speed device, is the auxiliary cam and shuttle movement by which the extreme speed of operation is transferred to the film. This entire unit dis (Equipment Service) 3335 Photo by Vnderwooil <£ Undertcoo'J New motion picture camera — see article on page 3340 places the regular register leaf and shuttle mounting when ultra-speed effects are desired, and is made with a view of quick change when in the field. The shuttle teeth differ materially with those of the regular movement in that eight teeth engage and film and draw it downward where as two only are used for normal speed work. Owing to the extent registration effected by this method the use of pilot pins are eliminated in the ultra-speed movement and as a further insurance against a possible lateral movement a marginal pressure plate is employed contacting the film along a length approximating four frames. It is quite obvious that the time required to expose a roll of film 400 feet in length is extremely short, being but fifty seconds. On lengthy subjects, or those requiring several minutes of actual photographing, this necessitates frequent changes of magazines where only the 400-foot capacity retort is used. A valuable feature of Bell & Howell construction is the employment of outside magazines which lends itself admirably for high-speed requirements, permitting the use of 1000-foot magazines, as is shown in the illustration. This furnishes ample footage for the average slow motion subject without the inconvenience of changes during the action which is highly important on subjects that will not permit of interruption. • Correct registration of the film is a matter that the Bell & Howell Company have exhaustively explored, and is the vital feature of their entire line of cine-machinery, including cameras, printers, perforators and splicing machine.