[rollei_list] Re: Lens coatings and veiling flare.


----- Original Message ----- From: "Ellestads" <ellestads@xxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Wednesday, July 08, 2009 7:52 AM
Subject: [rollei_list] Re: Lens coatings and veiling flare.


Please be careful cleaning interior surfaces of older coated lenses. Many of theses lenses (including Leica) ued soft coatings on the inner elements.
Cleaning can reduce those coatings.

Tim

Kodak certainly used soft coatings on some early coated lenses. These were premium lenses made beginning in about the late 1930s. I don't know what process was used to coat them but the coatings are _only_ on protected inner surfaces and are very delicate. While Marc beleives that Smakula, of Zeiss, invented hard coating I am not so sure. Zeiss may have had this technology but the record seems to show it was developed by a reseach group in the US during WW-2. Vacuum coatings can be relatively soft and the early ones were. What was developed here was the technique of baking the coatings in vacuo. Previously the coated lenses were removed from the vacuum chamber and baked in a separate operation. Baking in the coating chamber results in coatings nearly as hard as the glass. This method was developed as part of a research project for military optics. I don't know what instruments or devices it was applied to. The familiar Bausch & Lomb Navy binoculars appear to have been coated after manufacture. There is a good history of hard coating available at the Society of Vacuum Coaters web site:
http://www.svc.org/

Hard coating appears to have become available for civilian optics about 1946. Kodak and Wollensak seem to have been among the first to offer coated lenses. Some smaller manufacturers, Goerz for instance, evidently had to farm out their coating and were among the last to offer it. Its much more difficult to determine what technology was available in Europe. Keep in mind that nearly all European industry was seriously disrupted by the war and took some time to recover thus its possible that Leitz and others were using older soft coating technology for a time. This history of lens coating goes back a long way. H.D.Taylor, the inventor of the Triplet, was one of the first to recognize that flare reducing coatings were possible but he was never able to devise a practical method of coating. Resarch was carried out at many places including Zeiss and some curious ones like RCA. Smakula evidently was the first to realize that vacuum deposition (c.1935) was an excellent way of creating uniform coatings but those early coatings were not very durable. However, they were much better than chemical dip coatings of the type being developed at RCA. Those coatings will wipe right off the glass surface.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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