[rollei_list] Re: [slight OT] A Sonnar 1.5/50 + coatings at Kodak as of 1940
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Fri, 16 Jan 2009 09:31:20 -0800
----- Original Message -----
From: "Emmanuel Bigler" <Emmanuel.Bigler@xxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Friday, January 16, 2009 1:05 AM
Subject: [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, USA
dickburk@xxxxxxxxxxxxx
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