----- Original Message ----- From: "Emmanuel Bigler" <Emmanuel.Bigler@xxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx> Sent: Friday, January 16, 2009 1:05 AMSubject: [rollei_list] [slight OT] A Sonnar 1.5/50 + coatings at Kodak as of 1940
From Richard Knoppow :.....Kodak began coating quite early. A few premium Kodak lenses had soft coatings on internal surfaces by about 1940. These included the Eastman Ektar series...............a noticable ghost image of very bright objects in the image field, an effect which does not occur in the later, coated version.The Sonnar was designed with flare in mind..... The use of designs with a muntiplicity of cemented surfaces to avoid glass/air surfaces stopped almost immediately when coatings became available.Thanks you very much Richard !You mention that Kodak coated lenses as of 1940 ; this raises two questions:- could you elaboarte on the notions of soft and hard coatings ?- to the best of my knowledge, Zeiss (Smakula, 1935 ?) had a patent on the anti-reflection coating, how could Kodak get around this patent ? Or was-it simply that Zeiss did not have a US patent ? Or during the war, the question of enforcing patents was irrelevant ?(even if the US were not at war in 1940)Regarding patents and WW-II : I read in Pierre Glafkidès huge book on photographic physics and chemistry that German patents were cancelled afert the war. This, for example, allowed MPP in the UK to copy freely some features patented by Linhof for the Technika. Probably, some Carl Zeiss and Rolleiflex patents were also cancelled !-- Emmanuel
I am not sure what method Kodak used for coating. It may have been a chemical bath coating or an early form of vacuum coating. Chemical bath methods were known and some experimental work was done at Radio Corporation of America and reported in the RCA house journal. I can't find Smakula's patent. Marc has more history about this but I think the work may have been kept secet by the German government and no patent published. My patent search uses Google patents and searches only US patents. Its quite possible Kodak came on a vacuum deposition method independantly. A great deal of work on vacuum coating was done in the US during WW-2. This is detailed in a publication available on line from the Society of Vacuum Coaters site at http://www.svc.org Since all German patents were seized by the US government during the war there would have been no patent infringement consideration. The research was done by a consortium of US optical companies, mainly Kodak and Bausch & Lomb, and the US Army. It was discovered during this work that vacuum deposited coatings could be made much harder and more adhesive by baking them in the vacuum chamber. Previously the method had been to deposit the coatings and then bake the coated elements in air. This earlier method resulted in coatings which could be damaged by ordinary lens cleaning. Chemical bath coatings were even softer and less adhesive and could be wiped off the surfaces easily so were not really practical. Zeiss may have been aware of the vacuum baking method but there is not much evidence of this. The history of vacuum coating at the Vacuum Coater's site does give Smakula credit for originating one method of vacuum coating. There is a great deal of information on this site. I think the above defines the difference between hard and soft coatings. Coating for general purpose lenses was not practical until the development of hard coatings simply because the soft coatings were not durable enough. Kodak's use of soft coatings on some consumer lenses was, AFAIK, unique. Once the war came to an end hard coating began to be applied by several manufacturers but Kodak, B&L, and Wollensak appear to have been among the earliest advertizing hard coated lenses as early as 1946. While German companies undoubtedly had the technology the disruption of German industry prevented its immediate application following the war. Vacuum deposition technology has progressed very far since its beginnings. There are a great many applications in solid state electronics which probably drove research harder than optics.
-- Richard Knoppow Los Angeles, CA, USAdickburk@xxxxxxxxxxxxx
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