International projectionist (Jan-Dec 1947)

BI-PACK PHOTOGRAPHY {Continued from page 23) the aforementioned stereoscopic camera. The prisms were removed, since they played no part in the experiment which was purely for the purpose of determining possible sharpness or lack of same of the rear negative, as well as possible difference of density of the two negatives. Remembering the sad results of past tests, it was with some qualms that the exposed negatives were examined after developing. To the amazement of all, both negatives were perfectly sharp and well balanced as to density: the reason being that by the particular design of the camera gate, both films were held rigid during the exposure period by a back plate three inches long, the surface of which was covered by chamois leather. Further, the front plate was perfectly flat, highly polished, and without recess. Thus, conditions were perfect for the bi-pack test. It was then decided to repeat the test, u&ing a Bell & Howell camera. Again two negatives were exposed, developed, and examined: the result being a total failure as far as the rear negative was concerned, it being without sharpness at any point. Had not the previous test proved that a sharp negative could result under certain conditions, the tests might have again been abandoned, i But we had proved our theory once with excellent results and were able to realize that the failure of the second test was due to lack of adequate contact in the camera gate. Having proved that a sharp rear negative was possible, the rear plate of the Bell & Howell shuttle was built up with solder to the point where contact of the two negatives was assured. Color Value Requisites The next step was to consider color values, which required a filter of some nature to prevent those colors which were recorded onto the front negative trom reaching the rear negative. The logical procedure was to dye the front negative (which would be orthochromatic) with a red or red orange dye which would absorb certain colors and transmit those complimentary to that film. Several dyes were tried over a period of weeks without success, due to the fact that many dyes will react to unexposed emulsions and will create a chemical reaction which, when developed, shows as a heavy fog. While the dye tests were being made other filter methods were explored. One in particular proved to be an interesting experiment. We took a Wratten 23-A filter and cut a length the width of a picture area — 3 inches in length — and mounted the filter on two metal arms positioned so that the two negatives were threaded through the camera gate with the filter sandwiched between tlie negatives. The results were good as to color separation, but the method was a failure due to the rubbing of the emulsions against the stationary filter, thus creating rub marks on the filter A GREAT PAIR TO DRAW TO -FOR A FULL HOUSE! ITS war contracts completed, DeVry's famed "G-I" projector is now in production— readily available to the nation's Exhibitors. You have to see them to appreciate their modern design — their rugged construction — their beautiful finish . . . You have to see them in action to realize their rock-steady, flicker-free screening — the high-fidelity of their perfectly synchronized sound — from the softest whisper, the warmest tone, to the weirdest shriek! No flutter ... No hum ... No WOW! Talk with projectionists "Fight Infantile Paralysis . who've enjoyed year in, year out trouble-free DeVry performance in practically every corner of the Globe . . . Designed and built to specifications far in excess of generally accepted standards— priced so reasonably that ANY theater can NOW afford to buy them NEW — DeVry projectors of TODAY are indeed a great pair to draw to — for projectionist gratification, audience satisfaction! Request for details incurs no obligation. Use the coupon. . Join the March of Dimes" 5 TIME WINNER DeVRY alone has been awarded five consecutive Army Navy "E's" for Excellence in the production of Motion Picture Sound Equipment. DeVRY CORPORATION, Dept. IP Dl 1111 Armitage Ave., Chicago 14, Illinois Please send details about the NEW DeVry 35mm. Theater Projectors, Amplifiers and Speaker Systems. Name Address City State Theatre Capacity Asjsortatrii l&rtramr Ktujinma' A Society of I.A.T.S.E. Theatre Sound Service Engineers INTERNATIONAL PROJECTIONIST • January 1947 27