Re: [Rollei] Why the 6-element lens for 3.5Fs

["Richard Knoppow" <dickburk >]

- ----- Original Message ----- 
From: "Q.G. de Bakker" <qnu  
To: <rollei  
Sent: Thursday, May 01, 2003 12:29 PM
Subject: Re: [Rollei] Why the 6-element lens for 3.5Fs


> Nick Roberts wrote:
>
> > As an aside, has anybody ever tried the 2.8 Opton
> > Tessar?
>
> I would love to be able to say how good/bad Zeiss-Opton
2.8 80 mm Tessars
> are.
>
> But, alas, i haven't tested the ones i have yet, since
they need cleaning
> very badly. No point testing a dirty lens.
> I have asked the Hasselblad Users brethren (mine are in
"ancient" Hasselblad
> mount) if anyone knows how to get to the rear lens group,
but so far no
> answer.
> So maybe there is someone on this list who can tell me how
to disassemble
> these lenses (in such a way that they can be reassembled
again)? Or knows of
> any resources available anywhere that might help?
> I'd be grateful for any and all assistance!
>
  Exactly which lens are you asking about, the f/2.8 Tessar
or the Planar?
  If the Tessar, there is no rear lens group, there is a
single cemented component. The cell can be unscrewed from
the shutter but requires some disassembly of the camera.
  I don't have an f/2.8 Tessar to look at. The f/3.5 front
cell has a front retaining ring which is removed with a
friction tool. Probably the f/2.8 is the same. Larger
Tessars, such as the 135mm, f/4.5 found on old Speed
Graphics, have a threaded back cap which is easy to unscrew.
Like many other lenses Tessars tend to get hazy inside the
front cell.
  If the back component looks hazy its probably bad cement.
Recementing is not too difficult but almost all Tessar type
lenses of any manufacture use a burnished or spun-in
mounting for the rear component. These can not be opened
without damaging them. The glass is held in place by a very
thin lip which is burnished down over the lens. While they
can be pried up they can never be smoothed down again. The
usual method for dealing with these is to remove the lip in
a small lathe and replace it with a threaded cap. Precision
work.
  Zeiss lenses of the 1930s and 1940s seem for the most part
to have pretty good cement; I've seen relatively few with
edge separation. But the canada balsam used in lenses pre
about 1950 is sensitive to heat and cold and can oxidize and
crystalize at the edges if the paint seal is broken.
  A lot of old lenses which have low contrast are just
dirty.

- ---
Richard Knoppow
Los Angeles, CA, USA
dickburk  

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