Historically speaking.Did you know that the first coated lens appeared nearly one hundred years ago and occurred as a natural phenomenon? Some readers may have in their possession an old lens, such as an old Tessar that I own, that has a rather irregular looking coating on the front surface. It is the formation of such a tarnished surface that Dennis Taylor
Taylor observed that lenses that had acquired the tarnished surface had better light transmission than identical lenses without the tarnish tarnish, n 1. surface discoloration or loss of luster by metals. Under oral conditions, it often results from hard and soft deposits. 2. a chemical process by which a metal surface is discolored or its luster destroyed. . Attempts to produce the tarnished surface in the laboratory were not very successful and lens coating, although known, would not become a commercial feature for nearly fifty years. The early successful coating material coating material, n a biologically acceptable, usually porous nonmetal applied over the surface of a metallic implant with the expectation that tissue ingrowth will occur in the pores. Often a carbon polymer or ceramic substance. was calcium fluoride calcium fluoride n. A colorless powder, CaF2, used in emery wheels, carbon electrodes, and cements. and was discovered by a California professor in 1936. The process was not quite ready for commercial application because the calcium fluoride rubbed off easily. It wasn't long before the process was improved so that coated lenses were not only superior, but also practical. The superiority of the coated lens is not challenged nor argued; and it is safe to say that few uncoated lenses have been made during the last fifty years. Some strange facts surround the theory of lens coating and may be interesting to anyone who has not studied physical optics. Curiously, lens coating materials are metals and alkaline earths. It is difficult to view these normally opaque materials as substances that improve light transmission in lenses. The materials are deposited in a vacuum by sublimation sublimation, in chemistry sublimation (sŭblĭmā`shən), change of a solid substance directly to a vapor without first passing through the liquid state. of the heated coating material. The theory of the operation of the coating in a lens is similar to that for sophisticated beam antennas for propagation of ultra-high frequency radio waves Radio waves Electromagnetic energy of the frequency range corresponding to that used in radio communications, usually 10,000 cycles per second to 300 billion cycles per second. . By properly phasing the light reflected from the coating surface and the glass surface, the waves can be made to interfere and cancel each other. Most libraries have good books on optics and, although such books are highly technical and rather dull, you may find them also interesting. |
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