Showmen's Trade Review (Jan-Mar 1949)

SHOWMEN'S TRADE REVIEW, February 5, 1949 E-17 Newest Arc Lamp for Large Theatres Combines Mirror Optics with Rotating Positive Carbon Specifically Recommended for Drive-Ins, Motiograph Lamp is Rated at 19,000 Lumens An entirely different kind of arc lamp, intended for all large theatres and particularly for drive-ins, has been put on the market by Motiograph. It is a reflector-type lamp with a rotating positive carbon, and therefore unlike any other lamp manufactured today. Theodore O. Hall designed it for Motiograph and supervises its manufacture. It has been given the trade designation "Motiograph-Hall 75/115 High Intensity Arc Lamp." The manufacturer asserts it will deliver more light than any 70-ampere reflectortype lamp because the rotating positive carbon permits operation at up to 115 amperes; and also states flatly that it will put more light on the screen than rotatingpositive condenser lamps because of the claimed superior efficiency of mirror optics over condenser optics. The mirror in the new Motiograph-Hall lamp is 16 inches in diameter, product of Bausch & Lomb. Still further efficiency is secured, according to Motiograph, by a precisiontype automatic carbon feed which so positions the carbons with respect to each other that the gases are held back within the crater until they become super-heated to an extreme brilliancy; and at the same time holds the crater at the optimum focal point within a tolerance of not more than 7/lOOOths of an inch. Because of the superior efficiency of the lamp, it is stated, a heat filter is not needed for protection of the film; although use of external blower mechanisms such as those supplied with Motiograph Model AA projectors is recommended. Construction and Operation The base of the lamphouse is heavy gauge sheet steel. Front and back portions are aluminum castings. Both side-doors are double-walled. Auxiliary equipment includes the usual ruby glass observation ports and arc image projector. The 16-inch reflector is permanently mounted in the rear door. It cannot be moved, and must always remain accurately aligned with aperture and lens. Burning away of the carbons, and any fluctuation of the arc current beyond predetermined limits, sets the automatic feed control mechanism into operation to maintain the gap at correct position and length. A pilot light outside the lamp flashes notice to the projectionist whenever there is any material change in arc current, but in normal operation there is no need for him to intervene with manual adjustments. He can do so, however, if necessary. Normal trim consists of 9-mm. positives and 5/16" negatives, but the lamp is also designed to use positives up to 11-mm. Current range is 75-115 amperes. Tests made by the manufacturer indicate that the Motiograph-Hall lamp produces 19,000 lumens of light at an arc current of 85 amperes. Construction is of the unit type; the en Interior (left) and exterior views of the new Motiograph-Hall reflector-type rotating positive arc lamp, which is said to produce 19,000 lumens at a carbon current of 85 amperes. tire burner mechanism can be removed intact for servicing. Inner surfaces of the housing are smooth, to facilitate cleaning. A further advantage in cleaning is a removable false bottom that extends under the entire burner mechanism. Positive carbon contacts are of a bronze alloy, chosen as having the best heat conductivity consistent with resistance to scaling and majorities formed, and on 17 of those items the majority vote for or against — among those who believe the theatre should supply tools at all — either approached or reached unanimity. Among those members who feel that the theatre should supply tools for the projection room, or at least supply them under some circumstances, more than 80 per cent at least are in favor of furnishing the following: Screwdrivers of various sizes. Pliers of various sizes. Cutting pliers. Open end wrenches of various sizes. Soldering iron. Aligning rod (for optical alignment of lamphouse with the projector mechanism) . Trouble lamps. Rubber Tape. Friction Tape. (There are eight other items on which majority opinion was equally emphatic, but in opposition to them. Those will be listed below.) Lesser but still substantial majorities favor supplying the projection room with these items: Allen wrenches. Test phones. Tube puller. Opinion was exactly and evenly divided with respect to these items — whether to supply them or not: Socket wrenches. Neon test light. Tags for identifying wires. oxidation; contact surfaces are coated with a l/16th inch layer of pure silver. Although the Motiograph-Hall lamp is new, it is not untried. Experimental models have been in regular use in a number of drive-in theatres for over a year; the commercial model now offered to the industry at large incorporates the benefits of that experience. Only a minority approved equipping the projection room with: Test voltmeter. Ohm meter. Db meter. Test probes for use with meters. Picture test film. Sound test film. Binoculars for watching the screen. Very small minorities suggested the following tools and appliances: Pin punch. Small machinists' hammer. Combination ohmeter-voltmeter. Special thin flat wrench for removing projection head. Light meter. With respect to this last item, it will be remembered that there is an extremely strong majority vote in favor of providing the projection room with an aligning rod for optical alignment of lamphouse and mechanism, but a member of the minority that prefers a light meter for such work comments: "Experience proves to me that a light meter is the best guide to aligning arc lamps, especially when high speed lenses are used. Usually we gain 2 to 4 footcandles average on the screen by using a light meter in place of aligning rods, which are less accurate." Finally, three of the thirty items entering into the discussion were unanimously disapproved: Soldering torch. Pipe wrenches. Test oscillator. Projection Advisory Council (Continued from Page E-14)