From: Tor-Einar Jarnbjo (tor-einar@jarnbjo.de)
Date: 06/03/03-01:58:16 AM Z
> Well, I wish I had seen this before my last post:-)
> It turns out that there are at least two lenses called the
> Bistigmat. One was a lens of the convertible type, similar
> to the Convertible Protar, but with a different arrangement
> of the element powers, c.1890's. The other is this lens. I
> can't read Hungarian either but can make out some stuff from
> the text and illustration. This lens appears to be of the
> Steinheil "Periskop" type. A symmetrical lens with two
> meniscus elemenst, c.1865. These operate at f/15.
> The stop of the lens illustrated is a rotating disc with
> several stops on it. This type of stop was introduced in the
> 1860's but used for a long time after that. Iris diaphragm
> stops were introduced in the 1880's so one would guess this
> lens dates from not much later than that and probably
> earlier.
Thank you for that information. I called Rodenstock again today to confirm
this, and it seems as if someone made a mistake the last time I called them.
Lenses with serial numbers below 50000 are indeed manufactured before 1910
and they couldn't give any closer date on my 37000-Bistigmat.
> The illustrated lens appears to have a two position
> adjustment of some sort. Perhaps someone with better German
> than mine (just a few words) could make out what the words
> near the arrows next to the movable screw say.
The positions are marked "Mattscheibe" (focusing screen) und "Bildaufnahme"
(exposure). By setting the lens in one of the positions, you move the entire
lens a few mm back and forth. My first guess was that this is to correct for
the slightly different positions of the focusing screen and the film plane
in the camera. On the other hand is my impression, that the focusing screen
(at least in my camera) is sligtly further away from the lens than the film
plane, but putting the lens in the focusing position moves the lens closer
to the focusing screen.
Tor
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