[LargeFormat] Wollensak Extreme Wide Angle Lenses

[Richard Knoppow]

----- Original Message -----
From: "Clive Warren" <Clive.Warren@megacycle.co.uk>
To: <largeformat@f32.net>
Sent: Monday, April 21, 2003 5:10 PM
Subject: RE: [LargeFormat] Wollensak Extreme Wide Angle
Lenses


> >
> >It does look like it's construction is 2+2
>
>
> Quite a bit different to the f9.5 then. Mine is uncoated
and in a Betax #3
> shutter. The aperture is restricted by the construction of
the front and
> rear element holders. The shutter facing part of both lens
group barrels
> has a reduced diameter that I bet approximates to f9.5 So
there is no
> option of opening it up past the manufacturer's minimum
stated f stop.
>
> The idea of limiting the aperture may be due to focus
shifts on stopping
> down (?) and increasing lens aberations as the aperture is
opened up wider
> than the stated f stop. Both of these effects would have
affected the
> reputation of the lens as photographers tried to push the
boundaries
> perhaps......
>
> I guess as the f9.5 was a lot more expensive to construct
then is would
> make sense to the factory to continue producing the f12.5
and to drop the
> f9.5. Is yours a series III or IIIa?
>
> Anyway, good to know that the f12.5 is a good performer
and works well with
> colour. When I finally get around to using the f9.5 will
post some of the
> photos.
>
> Cheers,
>             Clive
>
>
  There are two possible reasons for the aperture limit. One
is that the image quality may become pretty bad beyond the
design limit. The rim rays may not be corrected beyond this
point.  The other is that the lens may be mecanically
vignetted beyond the aperture limit. I don't know the
claimed coverage for the f/9.5 Wollensak but its likely that
the maximum coverage angle is available only at small stops;
a common condition for most WA lenses. Mount the lens and
look at the back of it from the back of the camera. See
where the edge of the lens cells start to encroach on the
clear aperture. My guess is that if its opened much beyond
the limit imposed by the mechanical stop it will be
vignetted at _minimum_ coverage angles.

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