International projectionist (Jan 1963-June 1965)

Ill the light pro wise ovr the tops of the car the parking area and up into sk\ . In order to obtain the light-directing benefits of aluminum paint, the screen must be tilted forward toward the parking area by an angle about equal to the upward projection angle. In other words, the aluminum screen should face the projectors squarely. If this is done, a "low gain" aluminum surfacing will provide an effective reflect i\ it \ of about 150' < as an average over the central part of the viewing area, and may be a decided advantage when the screen is more than 110 feet wide. Experience indicates, however, that the results do no justify the increased construction costs of tilted screens when the width of the screen is under 100 feet. Fast Lenses and Beam Clearance In order to get all available from the arc to the screen, the jector lamp and optics must have maximum efficiency. This means that the rated mirror speed must be at least f 1.9, and preferably f 1.7. except in the case of "Suprex," or simplified high-intensit\ arc lamps. most of which have an optical speed of f 2.3. The projection lenses must be antireflection-coated and have a speed of at least f 2.0 or f 1.9 in the longer focal lengths and f 1.7 in the medium and short focal lengths This recommendation is a good one to follow when f 2.3 Suprex lamps are used. For the most efficient overall optical performance, the lens should be somewhat faster than the lamp, a desirable state of affairs not always possible to achieve. It is extremely important in driveins to insure unobstructed light-beam clearance through the projector, making sure that the rear-shutter case, heat baffles, and sight box do not cut into the arc-lamp beam and cause shading or loss of light. This is a serious problem with the Simplex Regular. Super Simplex. Brenkert, Motiograph. and other mechanisms designed before the davs of widescreen projection and fast shortfocus lenses. In some cases the obstructing parts can be cut away; in others it may be necessary to install special replacement parts. The small lens holder and hole in the front of the mechanism case produce severe vignetting, or fadeaway at the sides and corners of the picture, when short-focus lenses are used for widescreen projection. Modern mechanisms are designed with 4-inch diameter lens holders; and these are adequate for the fastest International Projectionist lenses in all focal lengths. Unless larger lens holders can be installed in old-time mechanisms, and the opening in the front of the case enlarged, special long-tube short-focus lenses must be used to avoid vignetting and loss of light. These special long-tube lenses not onlv eliminate the vignetting problem with Simplex Regulars and other old machines, but give the brightest pictures possible and a more consistentlv sharp focus than ordinary short-focus lenses do. They have an optical speed of f 1.7. are antireflection-coated, and are manufactured l>\ the Kollmorgen Optical Corporation under the series named "X-tended Super Snaplites." I'hev arc available in focal lengths of from l1^. to 3 inches, and all have a barrel diameter of 2.7!!1 inches. The optical design of an X-tended lens bears a resemblance to that of an opera glass, or Oalilean-tv pe telescope, used in reverse. The strong "'positive'" lens element faces the film, and maintains a nearlv con>lant beam diameter through the long barrel. The "negative" clement partialis counteracts the effect of the positive element and establishes the correct focus. This type of optical svstem has the advantage of an unusuallv ■.: I depth of focus, making the lens relativel) immune to the focus-ruining effects of film buckle. Clearer Pictures Owners <>f drive-ins requiring lenses of 3 inches or shorter E. F. for non-anamorphic widescreen projection should seriously consider the purchase of Kollmorgen X-tended Super Snaplites for brighter and much clearer pictures. These unusual lenses are so satisfactory in every way that they are even widely used in modern mechanisms having large lens mounts! The pictures are much sharper than is possible with ordinary short-focus lenses under the severe heat conditions imposed by powerful arc lamps. The use of reversed anomorphic lenses commends itself in drive-ins having "throws" so long that the focal length of the CinemaScope prime lenses would otherwise be excessive. Even the biggest lenses in the longest focal lengths are not quite so fast as lenses in more moderate focal lengths. Instead of expanding the horizontal dimension of the CinemaScope image 2 times to double the width of the projected picture, a reversed anamorphic lens squeezes the vertical dimension to % the normal picture height. The end result is the same, but the reversed anamorphic lens permits the regular March, 1964 SMjgi&fc^; m: uTi—MMf IPP^i **»% mm The small-diameter lens holder of most of the older projectors cut into the diverging beam of light rays thrown forward by fast lenses of short focal length, wasting light by shading the sides and corners of the picture. The short-focus f/1.7 Kollmorgen X-tended Super Snaplites eliminates shading by utilizing reverse-Galilean optics to "pipe" the light through the small-diameter lens holder without vignetting. In addition, X-tended Super Snaplites have such a great depth of focus that many exhibitors use them in the most modern projectors for the clearer, more evenly illuminated pictures they make possible. projection lens for non-anamorphic projection to be used as the prime lens for CinemaScope projection. Best Heat Reducer Water-cooled film gates are very desirable when arc currents are so high that the film might otherwise be warped, or permanently buckled, by hot gate rails. Air cooling helps remove heat from the picture area of the film, and is of positive benefit in curved gate mechanisms. There is some evidence that air cooling generates film flutter in flat-gate machines. When "cold" arc-lamp mirrors and water-cooled gates are used, air cooling is probably unnecessary. If ordinary silver-coated reflectors are used in the lamps, and the arc current exceeds 75 amperes, interference-type heat filters should be interposed in the arc beam. These reflect most of the invisible, heatproducing infrared radiation and allow most of the light (about 85%) to pass on. In order to avoid this rather serious loss of light, interference-type "cold" mirrors should be used without heat filters. "Cold" mirrors (such as the Strong TufCold and the Bausch & Lomb BalCOLD) transmit the useless infrared, but reflect light as well as silver mirrors do. Please turn to Page 13 'I