[LargeFormat] Observation...

[Richard Knoppow]

----- Original Message -----
From: "tripspud" <tripspud@transbay.net>
To: <largeformat@f32.net>
Sent: Tuesday, February 04, 2003 12:09 AM
Subject: [LargeFormat] Observation...


> Hi,
>
> I just saw two Ektars 203mm/7.7 close the eBay, one
> for 167.. and the other 430....  dollars.  One is mint
> the other still good plus.  What??
>
> Rich
>
   The 203mm, f/7.7 Ektar has become something of a cult
lens with quite inflated prices.
   This is a four element, air spaced lens of the type known
generically as a Dialyte. This differs from the "double
Gauss" lens, also four elements, air spaced in that all the
elements are either bi-convex, bi-concave, or have one plano
surface. The double Gauss lens (the Kodak Wide Field Ektar
is an example) has menicus elements with all surfaces convex
toward the stop.
  The Dialyte is the generic basis of such lenses as the
Goerz Apochromatic Artar, Gotar, and Dogmar, as well as many
other lenses, particularly process and copy lenses.
  The type has rather narrow coverage but is capable of
excellent correction. The Ektar, Dogmar, and some others,
have slightly greater power in the rear group to improve the
correction for distant objects.
  In general, this type of lens has rather stable
corrections with change in object distance.
  As far as I can find out the 203mm Ektar is the same
design as the previous Kodak Anastigmat No.70 with the
exception that the Ektar is coated.
  At one time, mostly prior to 1945, Kodak made many lenses
of the Dialyte type as Kodak Anastigmats with 70 series
numbers. There was also a 30 series KA which was a Tessar.
Most of these lenses were f/4.5 but a couple of others of
f/7.7 aperture were made.
  The curious thing is that the 203mm, f/7.7 KA and Ektar
were offered by Kodak as economy lenses for 4x5 and 5x7 view
cameras where the cost of a Commercial Ektar was not
justified.
  While these lenses have exceptional performance they are
very limited in coverage, the 203mm being just marginal for
5x5.
  They are very well corrected for spherical aberration so
are sharp in the center of the field wide open, but must be
stopped down to be really sharp in the corners, especially
of a 5x7.
  From Kerry Thalman's measurements the optimum stop is
probably around f/11 for 4x5 and f/16 or smaller for 5x7.
There is some variation in the lenses, especially the KA
version but he has tested at least one Ektar with quite
exceptional performance.
  A great many Kodak Series 70 KA lenses were supplied with
Graflex SLR cameras. Since the focal length must be a little
long to clear the mirror box the somewhat narrow coverage is
not a disadvantage.
  According to Rudolf Kingslake most, if not all, of the KA
70 series lenses, and maybe also the 30 series, were
designed by C.W.Fredrick, who was a self-taught designer.
However, so was Lugwig Bertele, the designer of the famous
Zeiss Sonnar.
  Kodak collected some really remarkable people.

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