International projectionist (Jan-Dec 1951)

HI -' Gl IP FIG. 3. Lens plates holding an array of 150 individual lenses: rectangular and hexagonal plates mirror and the intermediate condenser, is visible on the picture-aperture. The intermediate image-formation setup just represented can be realized, however, if the so-called honeycomb condenser is used. This consists of two lens-"holding" plates, as shown in Fig. 3. These will be interposed at a definite place in the light-beam of the mirror lamp, as shown in Fig. 4. Each lens plate has the same number of lenses. Now, the arrangement of the separate lenses is so contrived that each lens of one plate is coordinated with a lens of the second plate. That is, the focal lengths of the lenses of the first plate are chosen so that each lens always forms an image of the crater in the corresponding lens of the second plate. The lenses of this plate, in turn, will image every corresponding lens of the first plate on the aperture of the projector. All images of the individual lenses of the first lens-array accordingly superimpose themselves on the aperture. Thus with this intermediate image-formation system the whole of the light-beams coming from the mirror is subdivided into a large number — -about 150 — single lightbeams. In conformity to their practical application, the lenses of the first plate are rectangular, their images corresponding in size and shape to the picture aperture ; lenses of the second plate are hexagonal, approaching the circular form of the arc crater. The manifold subdivisions of the lightbeam by the honeycomb-condenser system has the great advantage of retaining the desirable characteristics of the intermediate image-formation system. High Operating Efficiency Assured Due to the fact that the desirable properties of the intermediate image-formation system are retained, the manifold subdivision of the light-beam by the honeycomb-condenser system has the great advantage that one can utilize fully the high operating efficiency of a concave mirror without a shadow of the carbonholder or the carbon showing up. The single lenses of the first array are indeed partially covered by this shadow; but this non-uniformity is obliterated at the aperture by virtue of the fact that the images formed by 150 individual lenses are superimposed In line with the characteristics of the intermediate image-formation system, there is also considerable independence from the exact imaging of the crater. Sidewise burning of the crater, for instance, is not perceptibly detrimental to FIG. 4. Optical system which utilizes "honeycomb" condenser. the uniformity of the illumination of the picture aperture. Moreover, it is also possible to attain uniform picture illumination with lower currents, i.e., a smaller crater. This mirror combination, therefore, has the following advantages: 1. Continuously uniform and color-free picture illumination, even with faulty carbon positioning and imperfect imaging of the crater, rendering unnecessary the otherwise customary attention to the arc and mirror knobs for truing up picture quality during projection. 2. Use of Beck (h-i) light even with currents from the present minimum down to 15 amps, so that h-i light, the superiority of which is well known — in particular for the projection of color films — can be employed even in the smallest theater. Not only does the honeycomb-condenser system bring about important operational advantages, but very likely a substantial simplification of the construction of mirror arc-lamps, too. No Guides, Position-Controls Guides and position-controls for the carbons and for the mirror are no longer necessary, since their precise position no longer has any great significance. It suffices if the carbons are fed at their ends by the carbon supports. Focusing knobs for the mirror can also be dispensed with. If such a lamp is once lined up correctly at the factory, no operating adjustments for maintaining picture quality are necessary during the time that the lamp is in use. The Ikosol honeycomb-condenser lamp manufactured by Zeiss Ikon VEB, Dresden, is shown in Fig. 5. This lamp is equipped with such customary accessories as an automatic carbon feed, combination arc-striking and light-beam dousers, as well as a latch-release device for the carbon holders. For use the lamp comes with an aspheric mirror of 300 mm. [11.811 inches] diameter. Evaluating the Honeycomb-Condenser Lamp By ROBERT A. MITCHELL THE introduction of the Zeiss Ikosol honeycomb-condenser lamp goes far toward meeting two very important needs, from the point of view of Soviet German motion picture technologists. The first is the need for satisfactory screen illumination — which need is universal and was recognized by International Projectionist years ago. The second is the need, they feel, for decisive Fig. 5. The Zeiss Ikosol honeycomb-condenser lamp. Note lightness and simplicity of this lamp. INTERNATIONAL PROJECTIONIST • April 1951