International projectionist (Jan-Dec 1947)

Automatic Acoustic Compensator By ROBERT A. HAINES, N.U.T. Member, Deleterious Dilatory Didactics I.P. takes pardonable pride in presenting to the scientific world this masterpiece of delusion. Sparing no cost, I.P. operatives waged a brilliant campaign to effect entry into the mental hospital wherein the author of this piece is confined. But, getting out was the trick. I.P. assumes no responsibility for any mental derangement that may result from a reading of this effusion. YV/ ITH reconversion plans well under way and many new theaters emerging from the blueprint stage, consideration is being given to providing automatically-compensated acoustics therein, so as to constantly afford optimum reverberation periods in auditoriums under all possible conditions of audience loading factors. Preliminary surveys indicate that the necessary working elements can be realized best through employment of a series of grill dampers basically similar to presently used ventilation grills. One face of each of the grill louvers would be treated with adherent material of the highest possible absorptive value, with the other face as nearly 100% sound reflective as possible. A further prime requisite is that each bank of louvers shall be equipped with modulator controls permitting adjustable rotation throughout 350 degrees of arc, or from full broadside through fully-feathered positioning. The number of grill banks specified and their placement necessarily would have to be calculated for each auditorium. The Tempo Speeds Up The foregoing provides the fait accompli o!. attaining the ends sought; however, the modus operandi contemplates certain salient features heretofore unemployed — even unexplored! It is proposed that a FairbanksMorse flat-bed scale be installed in each theater foyer modified as a sound absorption measurement chamber, through which each theater patron would pass. Provided with automatic sound level measurement operation, there thus would result the weighted absorption factor contributed by every individual entering the auditorium. These determined data then would be transmitted to an I. B. M. machine records unit for integration, the composited quotient of which would provide pulses passing through a Logarithmic Amplifier to an Ignitron Power Control for application to the grill Modulator Servo units. Reconciling Audience Vagaries While it might be thought that the preceding alone would satisfy the requirements (and admittedly we now have arrived at a practical proposal to meet dormant demands*) there yet remain those supplementary factors necessary to reconcile smaller but vital dynamic shifts within the auditorium/"* We must take into account .those wholly practical and demonstrable conditions including patrons' removal of outer garments, passage of individuals to and from rest rooms, movements of male patrons to more advantageous seating position with respect to the best looking females — and vice versa*** etc., etc., once the audience is assembled within the confines of the theater. Wherein Sanity Takes Flight The solution for evaluation of all audience maneuvers, though seemingly complex, readily may be accomplished through the use of Radar (Mk-VIII) with helical scanning through 168 degrees azimuthal, and 71 degrees elevation range, and having a maximum time constant of 395.2 microseconds. It is considered advisable to supplement this by installation of Veeder-Root resetting counters in each aisle, at the drinking fountains and by the candy vendors, for totalization of all such traffic movements. It is to be understood that these devices likewise shall couple into the Records Integrator, so as to provide for constant monitoring of both instantaneous and cyclical absorptive values for transmission corrections of the grill modulators. Thus simply, the final determinant of the complex transient quiescent absorptive factor is automatically translated into practical application, since the dynamic loading is thereby reconciled to the static reverberatory characteristic of the auditorium, predetermined by usual Fourier analytical procedure! Bibliography * Shepard, W". D. : "Sagacious Suggestions Surrounding Sonorous Sound Stifling." ** Smith, H. W. : "Life in a Putty-Knife Factory." '■"'* Cuppy, W. : "How to Tell Your Friends From the Apes." B. & L.'s Special Mechanism For Testing Photographic Lenses ANEW projection method of testing photographic lenses to insure precision quality control has been developed by Bausch & Lomb Optical Co. The projector is used for final inspection of the completed lens, mounted and ready for shipment. The instrument functions like a movie projector, except that the image it throws on the screen remains stationary. The image is magnified hundreds of times, depending upon the distance of the projector from the screen and the focal length of the lens. A target, imprinted with a series of minute replicas of a specially designed testing chart, provides the image which is projected through the lens being tested and onto a screen. Each chart is strategically placed on the target so that the entire image field, from the center to the extreme outer edges of the lens, may be examined for all types of aberrations. Remote Control of Lens Position Magnification is selected to meet the specific standards required of the lens. For example, a microscopic chart no bigger than the head of a pin, may be magnified 240 times for one type of lens, 300 times for another, etc. By remote control, an operator standing near the screen moves the lens back and forth within the instrument, until the image is in exact focus. The minute charts, magnified hundreds of times, are sharply defined in all instances, if no aberrations are present •in the lens. A second operator interchanges the lenses to be tested and checks uniformity of back focal length, another standard of quality, which is shown by a dial indicator on a micrometer scale attached to the side of the projector's front plate. Light Source, Optical System Heart of the projector is its light source — a 500-watt lamp and condenser system. The lamp is placed before a small, precision mirror which redirects some of the light normally lost through the optical system. A condenser lens, mounted in separate elements directly before the lamp, concentrates and intensifies the light. Aspheric surfaces to provide wide angle coverage are a feature of the condenser lens. Targets for testing lenses of long focal lengths may be readily interchanged in a rotatable metal holder mounted before the condenser. To keep the target from becoming overheated, the lamp is encased in a ventilated housing. Also a water-cell is an integral part of the optical system. Short Focus Condensing System A second, or short focus, condensing system, mounted in separate elements, is used to illuminate the screen properly. Directly behind the condenser is a removable ground glass which diffuses the light for certain types of inspection. A second holder, located in front of the short focus condensing system, retains the short focus target. The lens to be tested is placed in the front plate of the instrument, and projects the target image on the screen. A rotating support, moved by remote control to best operating position, holds the lens in place. A slow speed, 4-r.p.m. motor moves the lens back and forth along its axis, which is normal, or perpendicular, to the surface of the target. A remote control device, consisting of two switches enclosed in a small plastic case, controls the movement of the lens. Position of all component parts of the projector may be independently adjusted for maximum performance. Wants American Cine Equipment Cinefones, one of the largest India dealers in motion picture, radio and sound systems of all sorts is interested in purchasing in America the following equipment units: soundheads, projectors, arc lamps, amplifiers, speakers, heavy pedestals, rectifiers, stereos, curtains and controls, and all other electro-optical-mechanical accessories. Import licenses for a substantial expenditure have already been obtained by Cinefones, whose address is 3 Queens Road, Opera House, Bombay, India. Seeks 16-mm N Z. Sales Agency T. A. Fisher, Ltd., 22 Wigan St., Welling-' ton, New Zealand, for many years have acted as distributors for many American manufacturers of visual and sound projection equipment and other electronic apparatus, invite correspondence from manufacturers of 16-mm sound projection equipment who may be interested in a New Zealand outlet. Fisher already maintains an extensive 16-mm service and repair department. 24 INTERNATIONAL PROJECTIONIST March 1947