International projectionist (July-Dec 1934)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

October 1934 INTERNATIONAL PROJECTIONIST 15 sensitivity of the photographic emulsion. The plain carbon arc with only 17 per cent of its radiant energy in the visible and photographically effective ultra-violet range of the spectrum was satisfactory for the emulsions of an earlier day which were most sensitive to the blue, violet, and ultra-violet rays. Early panchromatic emulsions, while extending the range of sensitivity to all visible colors, were still low in sensitivity to yellow, orange, and red. A special type of flame carbon strong in orange and red emission was developed to meet the demands of that period for an efficient light source giving equal photographic effect for all colors. The development of present day supersensitive panchromatic emulsions, having much greater sensitivity to orange and red than the early types, calls for a light source of almost equal strength in all color bands; in fact, the color sensitivity of these emulsions is almost perfectly balanced to the radiant energy distribution of normal daylight. An improved white flame photographic carbon recently has been developed to match the sensitivity of these latest photographic emulsions, thus giving the motion picture studios the advantages of speed and coolness which characterizes the use of the carbon arc in photography. More than 40 per cent of the radiation from this arc is photographically effective. This new electrode is a metalcoated carbon 8 mm. in diameter with a core composed of rare earth chemicals of the cerium group. Special lamps developed for use with this carbon in the studio operate silently with continuous and uniform feeding of the carbons. These lamps overcome the objections to noisy and jumpy operation which were raised against the old types of arc lamps when sound was introduced into motion picture productions. The new studio carbon arc is operated on D. C. at 35 to 40 amps, with about 37Y2 volts across the arc. At this current density, 450 to 510 amps, per square inch (70 to 79 amps, per square centimeter) and with the relatively short arc length employed, the arc departs from normal characteristics of the regular white flame arc and takes on many of the characteristics of the high-intensity arc ; however, the crater formation in the positive carbon, while distinct, is not deep. The brilliant gas ball at the tip of the positive carbon consequently has a highly effective lateral emission. This arc at 40 amps, and 37^ volts gives about 9.330 candle power in the horizontal direction. A twin arc (2 arcs FIGURE 14 Spectral energy distribution of 40-amp. studiocarbon arc (A) and color sensitivity of supersensitive panchromatic motion picture film (B) in series) without reflector gives approximately 200,000 lumens at this current and arc voltage compared with 158,000 lumens for the regular white flame arc using 13-mm. carbons under the same conditions. On a 115-volt circuit this represents an efficiency of 43.5 lumens per watt as compared with 34.4 lumens per watt from the ordinary white flame twin arc. Radiant energy of this new carbon in the visual part of the spectrum is considerably greater than that of earlier New Mirror Guard Designed to overcome the troubles resulting from pitting by the new Suprex carbons, as well as to cut costs through the use of a relatively inexpensive guard for the mirror, there has been introduced by the Theatre Supply Company of New York a new product known as Mir-O-Guard. Mir-O-Guards are made in various sizes to accommodate every type of reflector. They are made with fine optical glass, and each Mir-O-Guard is of the same identical curvature as the mirror which it is intended to protect. Exhaustive tests made under actual operating conditions over an extended period of time, and with various sizes of reflectors, proved that the resultant light loss is less than 1%. Effect Large Saving Sponsors of the Mir-O-Guard base their sales campaign on sharply reduced costs with no loss in efficiency, the thought being that the purchase for use two or three times a year of Mir-OGuards, which cost from $3.95 to $4.95 each depending upon the size, is much more economical than would be the purchase at least twice a year of new reflectors costing from $15 to $25 each. The installation of a Mir-O-Guard before the reflector requires only a minute, with two tension springs to be set. Distribution of these guards is now being arranged by Theatre Supply Co., 235 Fourth Ave., New York City. ULTRA-VIOLET VIOLET BLUE | SREEN YELLOW] ORANGE] RED z "A < £> 10 z> ,-•' "*\ \ < £ o ~"b \ 4000 5000 6000 7000 WAVE LENGTH IN ANGSTROM UNITS types of flame carbons and shows a peak in that region where supersensitive films are least sensitive (Fig. 14). This new carbon with the improved silent lamps designed for its use is restoring the popularity of the carbon arc in motion picture studios for black and white photography and has proved very efficient in the latest color process. Intrinsic Brilliancy In many applications such as searchlights, spotlights, and motion picture projectors, it is essential that a powerful light be obtained from a source of small dimensions. In this respect the carbon arc is unsurpassed. The intrinsic brilliancy, that is, the candle power per square millimeter, for several types of arcs is given in Table III. For comparison, the intrinsic brilliancy of other light sources is included in the data presented. The carbon arc provides the basis for a ceaseless program of research. Steady improvements are being made in electrode manufacture as well as in lamp design. Longer electrode life, steadier operation, and higher electrical efficiency are being attained. New fields of application are being disclosed. Better adaptation to the many uses in which the arc now is applied is being achieved. The high efficiency of the carbon arc as a source of visible and ultra-violet radiation, the flexible and uniform quality of radiation it provides, and its comparatively extremely high intrinsic brilliancy, give the carbon arc a prominent and increasingly important place in the broad field of illumination. MALOY HOME ROBBED Five gunmen invaded the Chicago home of Thomas E. Maloy, business representative of Local 110, bound Mrs. Maloy and two other members of the household, and made off with $50,000 in cash and about $12,000 worth of jewelry, according to press reports from Chicago. Maloy was reported in Canada at the time of the robbery. Table III — Intrinsic Brilliancies of Light Sources Light Source Candle Power per Square Millimeter Source of Data Magnetite arc stream 6.2 Flame arc stream 8.0 900-watt special-tungsten-filament clear gas-filled bulb 26.6 Positive crater of cored, d-c low-intensity carbon arc 155— 175 Crater of a-c high-intensity carbou arc 280 Positive crater of nonrotating d-c high-intensity carbon arc 380 Positive crater of rotating d-c high-intensity carbon arc 400— 800 J Positive crater of d-c "super high intensity" carbon arc 1,000-1,200 National Carbon Co. Lab. 3un at zenith 920 950 .W. R. Mott, National Carbon Co. Lab. . International Critical Tables .Journal, Soc. of Motion Picture Engrs.