International projectionist (Jan 1961-Dec 1962)

FRONT SURFACE <COLD' MIRRORS FOR HIGHER EFFICIENCY, GREATER ECONOMY • Projection on big screens requires carbon arcs so powerful that the film may buckle out of focus, or actually blister, when ordinary reflectors are used in the lamps. But by replacing silvered mirrors with "cold" reflectors, picture-blurring, film-damaging heat becomes a thing of the past. Veritable miracles of efficiency and economy in motion-picture projection are made possible by the Strong TufCold, which brings the exclusive advantages of front-surface "cold" reflectors to every user of rotating-positive reflector lamps. NOT ONLY are the movies better than ever — they are also bigger, brighter, and more realistic, thanks to the tremendous light-producing power of modern projection lamps! But unfortunately, the inception of panoramic widescreen processes and the gradual raising of indoor-theatre screenbrightness levels from the old minimum level of 10 foot lamberts to an average of 201/9 foot lamberts (measured with the projector shutter running) have increased the heat problem to serious proportions. The average American indoor screen is about 35 ft. wide, and, of course, many are over 45 ft. wide. The average drive-in screen is more than 90 ft. wide, and many exceed 110 ft. Now, the many thousands of lumens of light needed to illuminate these enormous screens must be squeezed through the film aperture of the projector — a tiny "window" which, in 35-mm projection, is even smaller than a postage stamp! The delicate film may be disastrously overheated by the fierce blaze of concentrated radiation. The individual frames of film are exposed to the intense heat for only a fraction of a second; but during this short time they flutter in and out of focus so rapidly, and often so violently, that the picture is blurred. The projectionist cannot possibly adjust the lens for a clear picture when the film buckles. In extreme cases, the emulsion of the film is actually blistered, and the print completely ruined in one showing. Cold Mirror a Dream Come True The most practical solution of the heat problem is an arc-lamp mirror which reflects to the film and screen all of the light emitted by the crater of the positive carbon while permitting the useless, invisible, heat-generating radiations — the ultraviolet and infrared rays — to pass right through the mirror and into the rear of the lamphouse where their heat is dissipated by ventilation. Reflectors which act selectively upon the mixed radiations of the carbon arc so as to focus only the useful visible rays upon the film aperture, rejecting all others, are now available to every user of rotating-positive reflector lamps in greatly improved form — the Strong TufCold front-surface "interference" mirror. The advantages offered by TufCold arc-lamp reflectors are impressive. They almost completely eliminate the likelihood of film damage, they reduce buckle for clearer, steadier, more lifelike pictures on the screen, they in crease the brightness of the pictures by eliminating light-robbing heat filters, and they save money on mirror replacements by resisting scumming and pitting to a marked degree. The heat problem, now relegated to theatres not yet equipped with Strong TufCold reflectors, has two distinct aspects which must be separately evaluated by the purchasers of projection equipment and by the projectionists who operate it. Older Methods Inadequate The more urgent aspect of the heat problem is the print-damaging, buckleproducing effect of direct irradiation of the film by the concentrated rays of the arc lamp. In the days before tbe introduction of TufCold reflectors, this heating effect was mitigated by interposing heat filters in the light beam between the lamp and the projector mechanism. And even though heat filters have been improved since the days of the now obsolete infraredabsorbing glass, the use of heat filters has many disadvantages. Notwithstanding their relatively high efficiency, interference-type heat filters waste an excessive amount of light, namely, from 10% to 15% when the filters are new, and from 15% to 20% after they have been in use for International Projectionist April 196 ,