[rollei_list] Re: Contax
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Tue, 10 Apr 2012 09:10:21 -0700
----- Original Message -----
From: "Roger Wiser" <rwiser@xxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Tuesday, April 10, 2012 5:34 AM
Subject: [rollei_list] Re: Contax
Marc and Carlos, thanks for your reply. Here is more
complete information as requested:
LENS The exact wording on the front is" Sonnar 1:2
f=50mm Carl Zeiss Nr 1058406 " No "T" found. Lens has a
bluish tinge.
It is in VG condition, It has a filter on it. The f stops
are from 2 to 22.
Marc and others are more expert on dating this stuff but
the bluish tinge does not necessarily mean the lens is
coated. Some optical glass is vulnerable to corrosion of
the surface, this produces what amounts to a coating. Its
often a bluish color because its pretty thin. It has no
deleterious effect on the lens. check the back surface to
see if it has the same color, usually the back surfaces are
protected by being inside the camera and may be made of a
different glass. Optical coatings originated when H.Denis
Taylor, the inventor of the Cooke Triplet, noticed that old
lenses with corroded surfaces had higher transmission than
freshly polished ones. Taylor determined that it was due to
an anti-reflection action by the coating produced by the
corrosion. He tried to duplicate this chemically but was
not very successful. Various other methods were tried with
indifferent success until vacuum deposition was tried in the
mid-1930s by Alexander Smakula at Zeiss and others. This
early vacuum coating was quite soft, as was the chemical
coatings developed at RCA and elsewhere, and was usually
used only on protected surfaces of lenses. Hard coatings
were developed in the US during WW-2 research. These
coatings are vacuum deposited but are baked in vacuo in the
coating chamber. This type of coating began to be used on
critical military equipment during the war but was not used
for commercial products until around 1946. Eastman Kodak
used soft coatings on some lenses beginning around 1940. In
particular on the Eastman Ektar series, the predecessor of
the Commercial Ektar which differs only in having hard
coating, and in the lenses for the Ektra and Medalist
cameras.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
The history of vacuum optical coating is detailed in
material at the Society of Vacuum Coaters web site. A google
search will find it.
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