"murrayatuptowngallery" <murrayatuptowngallery@[EMAIL PROTECTED]
>
wrote in message
news:1192928072.513964.302640@[EMAIL PROTECTED]
> Hello:
>
> I just picked up a Gundlach 5x7 Rapid Symmetrical W.A.
> lens, roughly
> 8" f.l. (don't have it in my hands yet).
>
> The Rapid/Symmetrical names sound like a Rapid Rectilinear
> type, then
> I read that Gundlach had an extra element modification to
> the RR to
> get around a patent, so is it possible it might be 6
> element rather
> than 4?
>
> Then I read that some of the Gundlach lenses had
> disappointing
> centration. 6 vs 4 elements might make this worse?
>
> Finally, the seller said 'it ain't no Wide Angle'.
>
>>From this vintage, did W.A. mean anything else, or was
>>that a relative
> term that doesn't amount to wide angle these days? (Some
> older wide
> angles were really wide, so I'm confused).
>
> Is it a dog, worse than a dog, or a dog that only knows
> one trick?
>
> Thank you
>
> Murray
>
What speed, certainly not f/1 :-)
I can't find a Rapid Symmetrical W.A. but a Wide Angle
Symmetrical is listed in a 1926 catalogue at f/16. No
schematic is given but its described as a "wide angle
rectilinear type" covering 85 degrees. The No.5 has a focal
length of 8 inches and is specified for 8x10 plates.
There were some wide angle rectilinear lenses made by
others. The problem with the Rapid-Rectilinear type is that
they are not corrected for astigmatism so must be stopped
down for good sharpness away from the center. Astigmatism in
a camera lens is a different aberration than astigmatism in
the eye. In a camera lens it means that each point of light
in the image has two points of focus where the point is
focused as a line. At one point the line is axial, at the
other it is tangential. In between these two locations the
point is focused as a round blur spot. The less the
astigmatism the sharper the point. Since the size of the
blur is affected by depth of field astigmatism tends to be
minimised as a lens is stopped down.
The lack of correction of astigmatism comes from the lack
of glass types with the necessary properties at the time the
R-R lens was designed (1866). Until the development of
Barium glasses by Schott ("Jena glass, about 1890),
correcting a lens for both astigmatism and color was not
possible.
Ernst Gundlach was a curious character, Rudolf Kingslake
has a short biography of him in his book on lens history (1)
but also wrote a more lengthy bio of him (2). Gundlach
designed several lenses where he added an extra element
essentially go get around some existing patent. His version
of the Rapid-Rectilinear, which he called the Rapid
Rectigraphic, had three cemented elements in each half but
two were essentially just one of the elements in the R-R
split into two. The same with the Radar lens, essentially a
Tessar with an added element which evidently does nothing.
Probably Gundlach's most famous lens does not have his name
on it. This is the famous, or notorious, Turner-Reich
convertible. This is essentially a Zeiss Convertible Protar
with the same sort of split element seen in the Rectigraphic
and Radar. This lens was sold with all sorts of claims for
its superiority but the reality is that its not up the
Protar at all.
The centering problems apply mostly to the T-R lens,
which has 5 cemented elements in each cell. Lack of good
centering will disturb the performance of any lens but I
think the inherent performance of the T-R is not so
wonderful to begin with. In general, the more cemented
surfaces the more critical centering becomes. The method of
centering cemented elements was changed sometime around
perhaps the late 1940s but I can't be sure of the date. The
original method was to center each lens on a centering
machine and grind the edges as accurately as possible. The
cementing was then done by clamping the edges. A later
method is to center the lenses on the centering machine
after cementing but before curing. After the entire assembly
is cemented and cured the edges of the assembly are ground
concentric and parallel. This results in more precise
centering.
The centering machine is essentially a highly accurate
(with minimum run out) rotating tube on which the element to
be centered is fastened with a gummy substance. A point of
light is projected onto the lens and its image viewed in a
small telescope. The lens is then moved around until both
reflections (from front and back surfaces) are stationary
and stationary with respect to each other. For general
centering of elements the lens is then clamped by another
tube from above and the edges carefully ground to be
concentric and parallel. The same method can be used for
getting two lenses exactly together except there are than
four images to watch.
I would like to know if your lens turns out to be
something different. I have some access to older lens info
so might be able to find out what it is if not the lens
described above.
1, _A History of the Photographic Lens_ Rudolf Kingslake,
(1989) San Diego, The Academic Press ISBN 0-12-408640-3
2, "Ernst Gundlach: Nineteenth Century Pioneer Optician"
Rudlof Kingslake, _History of Photography_ 2, 361, (1978)
--
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Richard Knoppow
Los Angeles, CA, USA
dickburk@[EMAIL PROTECTED]
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