International projectionist (Jan 1959-Dec 1960)

width. This can best be achieved by use of the carbon arc. Table II shows the carbon trims available for 16-mm film projection; light produced through a standard 0.380 inch x 0.284-inch, 16-mm film aperture with shutter running and without film and heat filter; and also the life of the carbon trim. The carbon arc produces up to 3000 lumens of light on the screen through an F:1.5 coated projection lens and shutter of 72% transmission ; whereas the most powerful incandescent lamp produces 600 lumens under the same conditions G' 7. It can be readily seen that the carbon arc is capable of producing five times as much light as the incandescent lamp, thus the screen size can be more than doubled while maintaining the recommended screen bright 10 ness of 10 ± — foot-lamberts. 5 The film capacity of the largest standard 16-mm reel is 2000 feet. The running time of this reel, at sound speed of 24 frames per second, is 55V2 minutes, thus the life of each carbon trim listed in Table II is ample. Large Screens, Large Audiences The SMPE Committee on Non-Theatrical Equipment has recommended the following viewing conditions5: 1. Distance of farthest spectator from the screen should not exceed six times the width of the screen. 2. The distance of nearest spectator from screen should not be less than twice the width of the screen for matte screens, or two and one-half times the width of the screen for beaded screens. 3. Viewing angle of no spectator should be greater than 30 degrees with a matte screen, or 20 degrees with a beaded screen. The aforementioned recommendations and seating capacities — based upon the. use of 20-inch seats, 32 inches back-toback, with a limit of 14 seats between aisles as prescribed by the laws of some -.tales — show that presentation of 16 mm film with the carbon arc can be made before a maximum audience of 1000 persons at the optimum screen brightness of 10 foot-lamberts, or 1200 persons with a 20-foot screen at a brightness of 8 foot-lamberts. Larger audiences can be accommodated at the minimum screen brightness of 5 foot-lamberts. How far the screen brightness can or should deviate from the optimum 10 foot-lamberts depends upon the amount of stray light falling upon the screen. Picture quality is dependent upon the ratio of limits established between the screen brightness and the stray-light brightness on the screen. The straylight ratio in theatres should not be greater than 0.3% of the screen brightness8 The aforementioned maximum audiences are based upon the assumption that stray light is no greater than normally encountered in a theatre, a condition not always realized in rooms not designed for the exhibition of motion pictures. Economy and Ease of Operation Another advantage offered by the carbon arc is the decided economy of operation. At present-day carbon and power prices, the operating cost for "Pearlex" carbons is approximately 30 cents per hour, and 13 cents per hour for the "National" projector carbon. The 10 hour, 1000-watt incandescent lamp has an operating cost of approximately 60 cents per hour. Thus, the "Pearlex" carbons can be operated at about onehalf the cost of the incandescent lamp 6. Eastman Kodak instruction Bulletin 8-58GLP-A, Eastman Kodak Co. 7. Audio-Visual Equipment Directory, Fourth Edition, 1958. National Audio-Visual Association, Inc. 8. Estes, R. L, "Effects of Stray Light on the Quality of Projected Pictures at Various Levels of Screen Brightness", Journal SMPTE, 61, 257-272 (1953). 9. Lozier, W. W. and Joy, D. B., "A Carbon Arc for the Projection of 16-mm Films", Journal SMPE, 34, 575-579, 1940. TABLE II: ARC CARBONS FOR 16-MM FILM PROJECTION Carbon Trim* Amps. "National" Projector 6.4-mrn x 8-y2" Positive 10 5-mm x 7-V2" Negative "Pearlex" H. I. Projector 6-mm x 8y2" Positive 30 5. 5-mm x 6" Negative 7-mm x 12" Positive 46 6-mm x 9" Negative * All carbons are copper-coated Volts 50 28 Screen Lumens 750 1600 Life 135 58 min. 35 3000 80 min. *NOTE: The terms "National," "Pearlex" and "Suprex" are Trade Marks of Union Carbide Corporation. . „ while delivering 3 to 5 times as much light. Likewise, the "National" projector carbons can be operated at l/4th to l/5th the cost of the incandescent lamp and deliver 35% more light.* To an inexperienced observer, the carbon arc may appear greatly more complicated to operate than an incandescent lamp. Actually, it is no more difficult than threading film through the projector. Color Quality of Light The operating characteristics of the "Pearlex" carbon arc trims are similar in many respects to those of the "Suprex" carbon widely used for 35-mm film projection, but with certain modifications of color quality9. In the snowwhite color of light typical of the highintensity arc, the spectral energy distribution is characterized by an essentially even balance of energy throughout the different colors of the spectrum, which is particularly desirable for the projection of 35-mm color film. The 16-mm color film has been colorbalanced for projection with incandescent lamps, however, and these lamps differ from the high-intensity arcs in that their light is relatively very low in energy in the blue and very high in energy in the red portions of the spectrum. As a result, when 16-mm color film is projected by the snow-white light of the high-intensity arc. the blues are over-emphasized and the reds are subdued. The light of the "Pearlex" carbons has been adjusted to meet the requirements of the 16-mm color film by subduing the blue light and intensifying the red. This has resulted in a color of light which is satisfactory for both 16mm black-and-white and color film projection. Color temperature of the screen light produced by "Pearlex" carbons is approximately 4450 degrees Kelvin. The SMPE Committee on Non-Theatrical Equipment has recommended that color temperature of light delivered to the screen be in the range from 3000 to 4700 degrees Kelvin5. If, as is often said, one picture is worth 10,000 words, then the motion picture must be worth many times 10,000. Expansion of the use of 16-mm film for training and educational purposes is inevitable. The carbon arc is well suited for the projection of 16-mm film because it produces more light than any other available light source and at a lower operating cost. The increased screen size that can be adequately illuminated by carbons designed for 16-mm film projection makes practicable showings before a comfortably-seated audience of 1000 or more under conditions conforming to the best standards of projection practice. 10 INTERNATIONAL PROJECTIONIST • MARCH 1959