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166
BRITISH KINEMATOGRAPHY
Vol. 17, No. 5
Slide Cooling.
The filter in No. 1 condenser lens removes half the heat from the lightbeam, but a considerable amount of heat is still developed in the dark parts of the picture by the absorption of the light, and the slide has to be ccoled to prevent breakage. This slide cooler has been described recently 2* 3. Glass windows are placed close to each side of the slide, and air is blown through the two thin channels so formed. At 300 amps., 50 cu. ft. per min. of air are used (measured at the outlet), giving an air velocity of about 340 m.p.h. across the slide, and heat is removed from the slide at the rate of 360 watts. At lower light levels less air is required. The temperature of the slide is kept down to a safe level, and it is normal practice to project for many hours slides of any density and made on ordinary glass. For Technicolor process projection satisfactory results are obtained using colour positives on cut-sheet film, cemented on to a glass slide for support.
The air is drawn from the studio compressed air supply, the system being shown in Fig. 6. A filter removes dust and water, the pressure is dropped in an ordinary control valve and a silencer removes the very loud hissing noise from the air. After passing through nozzles into and out of the slide holder, a second silencer removes all noise from the air before it exhausts into the studio.
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COMPRESSED AIR FROM STUDIO SUPPLY
CONTROL VALVE
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SUPPLY SILENCER EXHAUST SILENCER
EXHAUST
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Fig. 6. Schematic diagram ofslide-ccoling equipment. Glass windows are placed close to each side of the slide, forming narrow channels through which passes air taken from the studio supply. Silencers remove the noise from the air.
The silencing of this cooling system has been given much attention. It is, relatively, extremely quiet, and what little noise it does make chiefly comes through the thick glass windows on either side of the slide. At the setting for 150 amps, there is a just-audible hissing sound at the projector. At 300 amps, this is quite noticeable at the projector, but no trouble has been experienced with the sound-recording at the set, and it is not necessary to place anything between the projector and set to reduce the noise.
Main Metalwork.
The aim in the design of the optical bed was to obtain a very strong structure on which the mounts of all the optical components would be very accurately positioned. Consequently, a single casting is used, and all the lens-locating surfaces were machined in one operation.
The main casting is supported from the central column through pan and tilt adjustments, the relevant dimensions being made as large as possible to ensure rigidity and freedom from backlash. There is no limit to the rotation in panning, and provision is made for tilting 15° upwards and 10° downwards. One turn of either control gives 1 ° of movement. Locks are provided directly between the main casting and the vertical column on each movement, which provide extreme rigidity ; they are designed so that the picture is not displaced as the lock is brought on.