International projectionist (Jan-Dec 1947)

increase created problems of heat transfer and ventilation requiring a radical departure from the conventional rotating high-intensity lamp design. The arc control motor, motor rheostat, arc switch and pin plugs were all removed from the heat of the body of the unit and located in a separate compartment on the rear lamp casting. Inasmuch as the balance of the carbon feedingmechanism is mounted on the front of this same casting, the whole forms an integral unit which may be easily removed for servicing. By these changes in design it was possible to build a lamp head, capable of continuous operation at 225 amperes, with no increase in length, only 4 inches increase in diameter, and slight increase in weight over the Type 170. The M-R Type 250 Process Projection Lamp The super high-intensity carbon trim used in the M-R Type 450 lamp has been used in the M-R Type 250 process projection lamp for some time. It is the result of a cooperative effort, by a committee of the Research Council of the Academp of Motion Picture Arts & Sciences, which included the National Carbon Co. and the Mole-Richardson Co., toward the design of a carbon arc lamp which will meet the critical requirements and high light output demand of studio process projection. Process projection is a system for inserting action backgrounds into sets built on studio stages. In this process a translucent motion picture screen forms the background of the set. In lighting the foreground care is taken that no stray light will reach the front of the screen. At a suitable distance behind the screen POSITIVE CARBON OBJECT1VI APERTURE I LENS B CONDENSER LENSES COMBINATION WATER CELL 4 RELAY LENS AIR JET FILM PLANE FIGURE 3. Relay is the projection equipment which supplies the screen images to form the background for an otherwise inanimate set. This action may be, for example, scenery viewed through a train window, the traffic behind a car on a Paris street, an ocean background for creating the illusion of a ship at sea, etc. The camera on one side of the screen is synchronized with the projector on the opposite side by means of interlocking synchronous motors. Projection vs. Front Light With the foreground area illuminated to the proper intensity for photography, the problems involved in obtaining sufficient projection light to fill a 20-foot wide, or larger, screen become serious. The Type 250 M-R process projection lamp was designed for this purpose, and because it delivers from three to four times the light intensity of the average theatre projection system, its features should be of interest to those desirous of learning the amounts of screen light available under highly specialized conditions. A theatre type projection system consisting of a Suprex lamp operating at 70 amperes with a treated surface F:2 FIGURE 2. Mole-Richardson type 250 background process projection lamp. WATER COOLED POSITIVE HEAD PHOTRONIC CELL POSITIVE CARBON POSITIONING SYSTEM NEGATIVE CARBON CARRIAGE ARC VIEWING SCREEN condenser system. projection lens will deliver up to 14,000 lumens. The M-R Type 250 lamp operating at 225 amperes and 75 arc volts, with an F:2 relay condenser system and an F:2 treated surface objective lens will deliver as high as 30.000 lumens from one unit. Under certain conditions Courtesy Farclot Edouart, Transparency Dept., Paramount Pictures, Inc. FIGURE 4. A complete background process projection equipment. even higher readings have been made. When more light is needed on one screen than is available from a single relay system, the triple projector is used.1 As the name implies, these units consist of three complete projectors, one facing the screen and the others at right angles projecting their images onto front surface mirrors which redirect them to the screen. In this manner three identical prints may be projected onto the same screen, thereby raising the level of illumination almost three-fold. Severe Requisites Satisfied To operate a lamp under such conditions of high current and requirements as to extreme accuracy of feeding and crater positioning, it was necessary to design a unit especially for process pro I. P. for July, 1946, p. 37. {Continued on following page) INTERNATIONAL PROJECTIONIST • March 1947