The Cine Technician (1943 - 1945)

100 T i I E (M N E T E C H N I C I A N July— October, 1945 Edited by A. E. Jeakins A New 35mm Projector with a New Light Source. Tiiii uli ire Schaffers, S.M.P.E. Journal, March, 1945. The development of the water-cooled high-pressure mercury arc — a high intensity light source oJ small size and low heat dev< Iopment — lias made possible the designing of a projector with mam novel features, one of which is a saving oi space which makes it possible to build two projectors one (in tiiii of the other. The mercury vapour tube is of quartz and is water-cooled. Two tungsten wires led through the end of the tube serve as i lectrodes. The tube contains a small amount of mercury and some argon Qas. The mercury vapour pressure is over 100 atmospheres and the light flux is 00,000 lumens. A rectifier supplies the direct current. Ignition voltage is 800 and working voltage 500. Currenl is 2 amp. The quartz tube is mounted on a semicydindrical housing backed by a specially designed mirror whii h gives a four image reflection of the mercury discharge. Together these produce a lighted surface about 0.316 ins. in width. Two mercury lamps (one is a spare) are mounted in a cylindrical lamp-holder; a piano-eon vex lens set in the side oi the lamp-holder receives light from the mercury lamp at a divergence of 90°. Refraction of this lens is relatively small as our surface is bounded by water. So a second condenser lens must be used. The shutter rotates in the space between the lenses. Light reaching the screen is very similar to that from a 45 amp. high-intensity carbon arc. Intensity is 2,500 lumens and is blue-white in colour. Circulating water is used to cool the lamps ; about 90% of the heat rays are absorbed and never reach the picture gate. Twin projector construction is made possible by the use of the mercury lamp. The him magazines are mounted in the space ordinarily occupied by the carbon arc and the monitor speaker and control panel are mounted in the base. The control panel carries two switches for controlling bass and treble, two plug-in switches for regulating volume from projection booth or auditorium, a switch that connects the monitor speaker to either amplifier, a volume control and three plug-in switches for film, photograph and mieropnone reproduction. There is also a lever switch connected by a flexibl cable io two shutters for instantaneous sound and i ire change-over. On the opposite side to the projector mechanism are the compartments containing the operating parts. The two upper compartments carry the ABSTRACTS p amplifiers, driving take-up r! itches and the controller drums which th ■ conned ons : rojector i mercury lamps a n d s a i e t y switches. The c o in p a rtment in the bas contains the amplifiers and power supply systems. E m projecmi qhanism is mounted on a cast iron d which permits a 20° tilt downward or a 10° tilt upw ard. The sound head is incorporated in the projector and the rotary sound drum shaft is coupled to a dynamically balanced fly-wheel. The controller drum mentioned above has I posil his which start the following actions: — (i| M itor is switched on — it has an auxiliary winding to ensure smooth starting. In this tion main end auxiliary windings are connected in parallel. (2) Auxiliary windin; runs at normal speed. (8) Mercury lamp is ignited at 800 v. (4) Mi rcury lamp i^ s.\ it die I to working volti o 500. The pro ji itor has sev< ral safety devices. If the tv in landholder is turned while the project cvat'ng i he : nplete inscallal ion itomatii dli i iii i It. [I a in a' ury lamp breaks down during opei tioii, the oper itor I irns the controller ih uu back to position 2 and revolves the twin lamp-holder 180°. The spare lamp goes into operation after he turns the drum bfi k to positions 3 and -1. The picture is intei rapted for a fev but i e si iund is not affe :ted. A magnetic oil filter system is another feal i this pri ije I \ pa r i strong pei manent nets ire mounl sd above the til ernritteni me nism. Sieel particles in the oil passing I ese magnets are attracted and trai ped. The magnets are easily removed for cleaning. is switched oh — i tor