International projectionist (Jan 1963-June 1965)

Screen luminescence was "better than new" after a 12-year-old Planetarium dome was repainted with velvet coating. Glare was eliminated. The dome is 65 feet in diameter, with a nine-foot horizon line and an apex at 41.5 feet above the center of the floor. Planetarium Dome Is Rejunevaled By New 3M Velvet Coating Housekeeping problems in a planetarium are compounded 1>\ its scientific orientation. This is especial!) true in the mallei of screen luminescence, a> demonstrated recentl) at the Morrison Planetarium of the California Vcadem) <>f Sciences, San Francisco: "Painting the 12-year-old dome with a virtually perfect light-diffusoating has enabled us to screen a better presentation todaj than at an\ time in the planetarium's history," according to Alvin C. Gundred. supervisor of instrument shops and technical advisor ot the planetarium. "That screen surface is better than new. After a dozen years, it became apt that the domed screen of this planetarium, opened to the public in November. 1052. was losing some of its luster. Quality of the projected imanes deteriorated so that the loss \va> readil\ noticeable t<> the experineced staff, Gundred said. This problem ol screen lumiiu cence is particularl) acute for a planetarium, where spectators must be able to see images of stars and planets clearl) from extreme viewing angles. Depending on the scat location, an imperfect screen surface can create either: 1 i Dull images caused by a loss of surface reflectance, or 2 i \ flared effect from too much reflectance at extreme viewing angles. Attention to image presentation qualities of a screen is part of the continuing maintenance function performed by Gundred. He supen ised much of the fourand-a-half year program for the building and installation of the projection instrument of this planetarium. Since then, he has been re sponsible for continuous maintenance and calibration of the instrument and of scientific exhibits. Qualtity maintenance has been a vital factor in the establishment of a record of perfect performance — Morrison Planetarium has never cancelled a show because of mechanical failure of its projection equipment. This is noteworthy because the instrument complex contains 141 projectors which cast images of some 3,800 individual stars and planets. Operation of this equipment utilizes 321 separate lenses, 304 operating bearings. 158 gears and 220 relay switches interconnected with more than four miles of wire. ^ears of continuous operation took their toll on the surface condition of the dome. To achieve glarelice luminescent surfaces in both the white and the black areas of the planetarium interior, Gundred selected ;i single coat of 3M brand velvet coating (Series 200). This material is an air drying lacquer designed for spray application and full coverage of any primed surface with a single eoat . I he 3M velvet coating is designed specifically to diffuse incident light while retaining a high reflectance capacity. In the case of the white lacquer applied to a domed screen of a planetarium, this means that spectators watching a star image virtuall) head-on from the projection angle are not bothered by glare. But the same image seen by persons on the other side of the room reflects more brightly and more exac||\ than ordinary flat paints. Result: the screen image remains uniform throughout the auditorium. The only pre-painting preparation necessary — aside from scaffolding — was to vacuum the top of the dome. Morrison Planetarium has a twoinch-thick pad of fiberglass above its dome to deaden echos and to protect the accoustical quality of the room. Lectures are carried to the audience through the perforated screen of the dome via 40 speakers. The screen perforation is a pattern of one 1/16" hole every 1/4". The vacuuming removed dust from above the screen, eliminating the chance of having holes plugged because lacquer adhered to dust. iP CARBON ARCS . . . for finest Projection . . . Compact Xenon Arcs JtoWuUne Ale Gasikotvi division • Brighter Light on Screen • Longer Burning per Carbon * More Economical ... / CARBONS, INC. j?mojv products moss LAMPHOUSES • Juntos/ POWER SUPPLIES by Cinemeccanica by Christie BOONTON. N.J. International Projectionist June, 1964 15