International projectionist (Jan-Dec 1954)

(Condenser I ma^e forming' lens iC Aperture T FIG. 5. The Koehler "intermediate-imase" condenser system for incandescent portable projectors. The condensing lens, not the bulb filament, is imaged upon the aperture, hence uniform light. and rugged electrical components which resemble those used in the American Motiograph Mirrophonic amplifiers. Ikovox speaker combinations, consisting of low-frequency dynamic PM speakers and cellular high-frequency horns in baffle cabinets, are quite like those put out in America. The two latest Zeiss Ikon reflector arc-lamps are the Ikosol II for normal (low-intensity) carbons up to 35 amperes and for Beck (high-intensity) carbons up to 50 amperes, and the Magnasol IV for Beck carbons up to 80 amperes. These are illustrated in Fig. 4. Although these units resemble American simplified HI lamps in their general particulars, several significant differences require comment. Instead of being placed at the extreme rear of the lamphouse, the mirror is positioned farther forward, as in the older American reflector lamps designed exclusively for LI operation. This position has always seemed desirable to the writer, for it permits better facilities for adjusting the mirror-aperture distance to obtain maximum uniform illumination on the screen. Two Feed Motors Although we do not find automatic "photronic" arc-positioning in these German lamps (a feature of several American rotating-positive lamps) the Ikosol II merits attention by having two separate feed motors, one for the positive carbon and one for the negative. This arrangement (of which we do not entirely approve) eliminates the need for differential gears and cams which, however, are found in the Magnasol IV. Because these lamps (especially the Ikosol II) may be used for LI as well as HI projection, the ratio of negative to positive-carbon rates of feeding can be varied throughout an enormous range. The controls of the Magnasol IV are neatly arranged on a panel beneath the door on the operating side, eliminating an array of knobs on the rear of the housing and permitting the projectionist to operate the projector without rising from his seat by its side. The door of the lamphouse carries the crater screen as well as a darkglass window, and is opened by sliding it up into the lamphouse. So also with the Ikosol JI. The housing of both lamps is double-walled and well ventilated. The Ikosol II, designed primarily for use with the amazing "Wabenkondensor" (Honeycomb Condenser) to permit even and uniformly white screen illumination with even the very lowest HI arc currents, and without much attention to the evenness with which the positive crater forms, has very few knobs. The mirror adjust ments, moreover, are inside the lamp, and may be reached by raising the door slightly. We should not like this feature if we were operating the lamp without the Wabenkondensor, but with this special optical system the mirror adjustments need not be altered once they are set for maximum light. Lamps Are Lighier The first models of the Ikosol (not the present model) have been criticized by European projectionists for flimsy construction, and while it is true that German lamps are lighter and perhaps less substantially built than many American lamps, a high degree of ruggedness and mechanical stability is claimed for the Ikosol II. While limitations of space prevent a discussion of the caboose-shaped predecessors of these modern German lamps (Magnasol I, II, and III, Ernesol, Kinesol, Artisol, and Ikosol I), attention is called to the influence which American lamp design has exerted upon the kerosene-drum shape of the lamp housing and upon such details as the carbon-consumption scales, arc-indicator screen, spatterguard douser, and plain glass mirror shield (which, however, covers only the bottom portion of the mirror) . The mirrors employed in these lamps — 300 mm. (11% in.) diameter for the Ikosol II and 356 mm. (14 in.) diameter for the Magnasol IV — are aspheric reflectors made of Ignal glass and notched out at the top (like the old Peerless LI reflectors) to prevent FIG. 6. The Wabenkondensor, or honeycomb condenser, a special modification of the Koehler principle for use with HI mirror arcs. The mirror is imaged by each rectangular lens of plate A upon each corresponding hexagonal lens of plate B. The lenses of plate B, in turn, superimpose ih* images of the rectangular lenses of plate A upon the operture to give uniform brightness. 12 INTERNATIONAL PROJECTIONIST • JANUARY 1954