International projectionist (Jan-Dec 1946)

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BUBBLES IN LENSES [Continued from page 10) carbon monoxide is practically negligible. Millions of amateurs and many thousands of professionals have been using "lenses witb bubbles" without noticing any adverse effects. Since the bubble content in optical glass is continuously going down, they will hardly ever have a chance, even under some very, special condition, to observe a "bubble effect." What should a photographer or a projectionist do about bubbles in a lens? From what was previously said, the answer is obvious: he should do nothing. if his primary interest lies in the lens performance and not in conducting some superficial observations. The fact that a lens contains bubbles or is free from them has no basic significance. Of fundamental importance is whether the lens is precision-made, and whether the glasses used in it are insufficiently free from inhomogeneity which, although concealed, may have disastrous effects. Superficial Inspection Valueless All these factors do not reveal themselves under superficial observations. An experienced optical designer or an optical engineer can, after a careful examination of a lens, say a few words about its design, about its good or inferior workmanship, and about some defects in glass which remain hidden from untrained eyes. If the lens is of an old make, he may even take a chance on guessing the type of glass by its bubble content. He will in no case, however, condemn a lens only because of a few bubbles in its components or because of some other appearance defects unless they are so pronounced that it becomes obvious that the lens was not made in accordance with the generally accepted rules of the optical art. For the lens designer, as well as for the lens user, the value of a lens is determined by its performance. The designer rarely worries about its bubble content because he knows that most of them can be produced sufficiently free from bubbles to satisfy his critical requirements, and he would not handicap himself by limiting the choice only to "bubble-free" glasses. This is because his primary task is to produce a wellperforming lens, using the best suitable formulas and glasses, and not to produce a bubble-free lens, even if by doing so he cannot secure its good performance. There are some cheap glasses which can be easily produced free from bubbles but are nevertheless unsuitable for most purposes of the modern optical design. The lens designer is not disturbed by this fact. On the other hand, if a glass be produced tomorrow of some unusually favorable optical characteristics and a that bubbles in glass would become the high bubble content, the designer would "marks of distinction" oi some ultra not hesitate to use it in order to improve modern anastigmats. his formulas and to assure superior per The user is entirety justified in his formance. Thus it may happen again desire to gel the best performing lene * A TRIUMPH in design and construction Setting a new standard in screen performance. See it now at your Motiograph Dealers. M0TI0GRAPHf INC. 4431 W. Lake St., Chicago 24, III. EXPORT DEPT.: J. E. ROBIN, INC. 330 W. 42nd Street, New York, N. Y. U. L. approved . . . eliminates fire hazard. MicroSwitch safety cut-off — when door opens, motor stops! Motor does not transmit torque to operating parts. Reel-drive Dog... prevents broken keys. Available through Theatre Supply Dealers. GoldE Manufacturing CO. LowMaiiitenaoceCost Modern, Compact DesHjp 1Z20-R West Madison S» Depl. R, Chicago 7 Positive Friction . . . Will Not Clinch Film v__. "Tilt-back' Case . Reels Can't Fly Off ,_«/ INTERNATIONAL PROJECTIONIST • December 1946 31