International projectionist (Jan-Dec 1937)

18 INTERNATIONAL PROJECTIONIST April 1937 PROJECTION REQUISITES OF THE BERTHON-SIEMENS LENTICULAR COLOR FILM By EDGAR GRETENER SIEMENS & HALSKE A. G., BERLIN-SIEMENSSTADT, GERMANY In the past few years in Europe the lens-screen method for color films has been further developed. The most active group worked with the inventor, Rodolphe Berthon. Their interests are embodied in Opticolor A. G., Glarus, Switzerland. At the request of this company, Siemens & Halske A. G. (Berlin), in connection with other firms, developed the method into an industrial process. It has received the name Berthon-Siemens Color-Film Process. During the 1936 Olympic games a short film, made by this process, was shown publicly in Berlin. It is believed that this represents the first time in the world that a lens-screen colorfilm (35-mm.) has been shown successfully on a motion picture theatre program. Additional films are being made. THE light requirements for projection of lenticular film are about ten times as high as those of the blackand-white film. The losses occur in the reproduction filters and through the reduction of aperture necessary to overcome vigneting of the illumination and reproduction systems. Besides the necessary increase in intensity of the projection light, special requirements are created as to the quality of the illumination in the projector aperture. The illumination systems used at present for black-and-white film all produce light rays with energy distribution that varies for different angles of the image field. The only necessary condition for black-and-white projection is an approximate proportionality of energy in the light rays belonging to the individual image points. This alone fulfills the condition of approximately constant illumination of the whole image field. The special conditions for the illumination of the lenticular film have been fulfilled by creation of a new type of arc lamp. Considerable increase in the efficiency of illumination was attained as compared to present illumination. For small theaters a pure carbon arc was developed. In accordance with the form of the picture aperture, square carbons are used. A stabilizing arrangement at the hot end of the positive carbon effects the concentration of the total discharge upon the front surface and protects the shell from oxidation. A magnetic field of a special type, with its axis parallel to the carbon axis, takes care of the stabilization of the arc. It is constructed so that rotation of the total discharge takes place at such high frequency that the homogeneity of the crater for the illumination time of a single frame is assured. The space stability of the crater is so great that only a small safety margin of the crater image over the film-gate area is required. The positive and negative carbons have a common horizontal axis. The thermal lifting force on the arc is practically equalized through the electro-dynamic forces of the stabilizing field. Large theaters, use high-efficiency lamps of very high intensity. Here also, new ways had to be found. In the existing high-intensity lamps, employing the Beck-effect, a deeply burned-out crater prevents the reflection of the luminous gas ball to the sides on account of the high crater walls. A considerable part of the current goe*-. to the carbon shell, and is therefore lost for light production. The light-intensity distribution is not homogeneous, and is disturbed by flames emerging from the space between the shell and the core. In the newly developed high-efficiency lamp1, square carbons are used. The lamp burns with absolute freedom from soot. An intensely luminous gas ball is visible which extends well in front of the positive carbon and therefore can radiate laterally without obstruction. The flame gases are absorbed by a cover surround 1Conventional Suprex-type arc. ing the negative carbon and escape through the bore of the reflecting mirror. In order to give an idea of the efficiency of the new lamp, it may be stated that with a current of 60 amperes, the density (intrinsic brilliance) in the crater was measured as 800 candles per sq. mm. Further increase of screen brightness above the limit reached with the new lamp could be attained by development of a special projection screen. The screens that are at present in common use in motion picture theatres, and which provide diffuse reflection, throw a great deal of the light from the projector upon the ceiling and the walls of the theatre. The new reflector type of screen reflects the light only in those directions in which it is intended to go. Metal sheets are used in constructing the reflector, and small concave mirrors are rolled into them of such form that the desired diffusion diagram is obtained. The dimensions of the elementary mirrors must be kept very small, so that one million elementary mirrors are present in one square meter. ■ On the basis of present conditions in German motion picture theatres, an increase of screen brightness by a factor of 3 can be obtained through introduction of the new screen. The precision requirements of the elementary mirrors and the uniformity of impregnation must be extremely high, since otherwise changes of brightness appear at the borders of the individual metal sheets. Upon projecting a color-film, the viewing conditions are different from those when the object is viewed directly. The colored image appears luminous in a black frame. The connection with the surroundings is missing. The change from one scene to another occurs in jumps, so that the eye has no time to adapt itself to the changed mood. If pictures taken under varying conditions of illumination are combined into a single film, one gains the impression that, for (Continued on page 30) A Fine Travel Book by a Boston Projectionist I don't recall any projectionist who ever won a Nobel prize for literature, or even an Academy award for a scenario, but I am faced with the evidence that Arthur Foley, projection chief at the RKO Theatre in Boston has written one of the most engaging travel books ever to fill my vision. The book is titled "Breezy Adventure," and a more apt title could not have been selected, so racy and invigorating is this narrative of travel on two continents. Travel books usually are soporific in their tireless chant of architectural attainments and native customs, all of which Mr. Foley ducks to indulge in some pretty stiff and straight sentence-punching anent those experiences which befall a traveler with the will to have fun and to avoid the commonplace. The charm of Mr. Foley's work lies in its ability to make one forget the book and imagine the author sitting opposite and reminiscing over a spot or two of this or that. The bleak printed page is blotted out and supplanted by a warm and human personal exposition of carefree travel days in Europe, in Northern New England and in Canada. I dipped into the book with only a mild curiosity; before I had finished it, in one reading from which I could not tear myself away, I was proud to have a copy of this work inscribed to me by the author. Published by Bruce Humphries, Inc., 306 Stuart St., Boston, this book of 213 pages sells for $2. It will give ten times that amount in pleasure.— JJ.F.