[LargeFormat] Kodak serial numbers and lens coatings

[Richard Knoppow]

----- Original Message -----
From: "Michael Briggs" <MichaelBriggs@Earthlink.net>
To: <largeformat@f32.net>
Sent: Wednesday, November 06, 2002 5:25 PM
Subject: Re: [LargeFormat] Kodak serial numbers and lens
coatings


>
> On 07-Nov-2002 Richard Knoppow wrote:
> >   FWIW, the "circle-L" mark and the trade-name
"Luminized"
> > for hard coating appeared first about 1946 or 1947.
Kodak
> > _soft_ coated some lenses from about 1940. These were
the
> > Eastman Ektar, predecessor to the Kodak Commercial
Ektar,
> > the lenses for the Kodak Ektra camera, and lenses for
the
> > Kodak Medalist. There may have been others. Soft
coatings
> > are deposited in a chemical bath. They are very soft and
can
> > be damaged or even removed by ordinary lens cleaning.
They
> > were applied to surfaces in sealed cells.
> >   It is diffucult to find data to date vacuume deposited
> > lens coatings. The processes was developed at Zeiss as
early
> > as 1935 but does not seem to have been used by them, at
> > least not for common optical products. U.S.
manufacturers
> > began hard coating in 1946 or 47, some later. I think
all
> > Kodak and Wollensak lenses were coated beginning in
1947.
> > Wollensak's trademark was a large C with a W inside it
for
> > "Wocoating". There were also aftermarket coating
services
> > available.
>
> Rudolf Kingslake, in a 1947 article about WWII aerial
lenses that appeared in
> the Journal of the Optical Society of America, states
"From the very
> beginning of the war, .... the glass-air surfaces of all
aerial lenses were
> coated with an antireflection film.  This was of soft
calcium fluoride at
> first, but later hard coatings were developed that offer
as much resistance to
> abrasion as the glass itself."
>
> Are the chemically deposited soft coatings that Richard
refers to the same as
> the calcium fluoride that Kingslake mentions?
>
> Today the cheapest single coating is typically magnesium
fluoride, and I
> suppose that this was the material of the first vacumn
coatings, and is likely
> to be the "hard coatings" that Kingslake refers to.  A
1955 Kodak product
> booklet that I have says that Kodak Lumenized lenses are
coated with "a thin,
> hard coating of magnesium fluoride".   A 1951 Kodak
brochure defines Lumenizing
> as a "Kodak process for hard-coating the glass-air lens
elements" which is
> "produced in an evacuated bell jar by evaporating a
fluoride salt onto the
> surfaces of the lens elements."
>
> From my examination of Kodak Aero-Ektars, even ones as
early as 1943 (based on
> serial numbers beginning EA), I find that they are all
coated.  The coatings
> are in generally good condition and I think are
inconsistent with soft coatings
> that might be removed by ordinary lens cleaning.  The
coatings appear similar
> to those of coated lenses of the 1950s.  I guess that
Kodak was vacuum coating
> some military lenses at least as early as 1943.  These
lenses lack the circle-L
> trademark, but there would have been no need for the
marking since the military
> would have purchased based upon detailed specifications.
My guess is that
> Kodak's vacuum coating facilties were reserved for the
most important military
> optics during the war and were used for civilian lenses
after the war ended.
>
> --Michael
>
>
   I once knew more about this than I can remember now. I am
pretty sure cumulative indexes for the _Journal of the
Optical Society of America_ for the period between 1940 and
1950 would have considerable information on lens coatings of
the time.
   RCA experimented with chemical coatings in the late
1930's. I believe the object was to reduce flare in the
microscope objectives used for photographic sound recording.
There was at least one paper in the _RCA Review_ at that
time. I read it in the dim, distant, past but have no memory
now of the details or what materials were used. I think the
same woman who did these experiments also published a paper
on "soap bubble" coatings; maybe its the same article.
  I will check the L.A. city public library to see if the
have the Review in their holdings. I read them at the UCLA
engineering library long ago. All their old stuff is burried
and it takes forever (and a fortune in parking fees) to find
anything there.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com