International projectionist (Jan-Dec 1956)

tions may stick when unwound, or if not projected, may be spoiled by a mold that lives on gelatine. Low temperatures are not necessary for the long-term storage of processed safety-film prints, but the relative humidity of the storage-vault air should not exceed 50%. On the other hand, air much drier than 40% relative humidity may cause partial dehydration of the base material and result in shrinkage and brittleness. Prints in active circulation should not be refrigerated at all. We must warn against keeping prints in a freezer, for they might become very wet when removed. Projectionists in cold, damp climates should guard against rewinding film received on bitterly cold days until the rolls have had a chance to warm up to the temperature of the projection room. It is especially necessary to avoid projecting cold film. It is true that damp film gets less hot running through a projector than does dry film. The temperature of film is somewhat lowered when moisture evaporates from it; but this phenomenon may buckle and otherwise damage the film as well as interfere with satisfactory projection. On the other hand, it is also true that the film does not get as hot during the first run as it does during subsequent showings for the obvious reason that the projector mechanism does not attain maximum temperature until an hour or two after the start of a continuous performance. Even though it is the heat produced by direct arc irradiation that damages the emulsion of the film in some cases, most of the heat absorbed by film during projection comes from the hot gate runners and tension pads by conduction. It is the heat transferred from the gate that makes the film perceptibly warm as it winds up on the reel in the lower magazine. A "cold" projector — whether it be a machine just started up to run the first reel of the day, or a machine having a watercooled gate — does not heat the film appreciably even when the arc radiation is strong enough to blister the emulsion. HEAT-ON-FILM PROBLEM (Continued from page 12) even with heat filters. No condenser lamps were available for testing; but it may be assumed that slightly higher amperages may be burned in condenser lamps for increased picture brightness before the deleterious effects of heat make themselves apparent. But even though the thick lenses of condenser lamps absorb somewhat more infrared than does the thin glass of a mirror, manufacturers of condenser lamps recommend the use of heat filters at high arc currents. Air Cooling Systems Air cooling of the film in the aperture of the gate is a very popular method of minimizing the bad effects of heat absorbed by the emulsion. One form of air cooling, of more value for reducing the temperature of the mechanism than for protecting the film, is provided by specially designed rear shutters, both the cylindrical and "fan" types. The vaned cylindrical shutters of the Motiograph and many German projectors have proved very satisfactory for drawing cool air over the film gate and rear of the mechanism, expelling it toward the lamphouse. Modern air-blast apparatus is designed to force a stream of cool air upon the emulsion side of the film at the aperture. The air reduces the temperature of the emulsion only slightly (about one-quarter as effective as a heat filter), and unless directed upon the film in a special manner, the air stream may induce distortion of the film and focus-ruining flutter. The film-cooling air-blast attachment for the Simplex X-L is one of the more satisfactory arrangements. A "pulsed" stream of air is blown against Splicing Problems Are Coming! If you're thinking of ordering a new splicer, be smart and investigate the Ace Clear Vision Splicer, a completely new method. * It makes a strong splice on acetate. * Will splice the new DuPont Cronar base and join Cronar to acetate. * It is non-magnetic — Will not injure CinemaScope soundtracks. Ace Electric Mfg. Co., 1458 Shakespeare Ave., New York 52, N. Y. the emulsion side of the film while a continuous "compensating" stream plays upon the celluloid side. By timing the rear blasts so that air blows upon the film emulsion for a short time at the moments when the blade of the shutter opens the light path, film flutter is greatly reduced. Without the air-pulsing modulating valve, air cooling of the film does not appear to reduce flutter, and it has the bad effect of inducing a "positive," or toward-the-lens, pincushioning of the film frames. Even the most satisfactory air-cooling device does not do much more than prevent film shutter by the pulsed pressure of the air blast. The actual cooling effect is relatively small. Blistering of the emulsion occurs with air cooling at arc amperages only slightly higher than the currents known to blister film when no cooling is used. To be specific, approximately 75 amps, in simplified HI mirror lamps, or 80 amps, in rotating-positive mirror lamps, is the maximum when air cooling, alone, is used. At 85 amps. Superb HILUX 152 STILL the lowest... and one of the finest... HILUX 264 152 FIXED & VARIABLE ANAMORPHIC LENSES $107.50 $395-00 MMM EACH PER PAIR See your Theatre Supply Dealer or write us directly . . . NOW PROJECTION OPTICS CO. R O C H,E STER, NEW YORK INTERNATIONAL PROJECTIONIST • March 1956 33