[rollei_list] Re: Diagram of Heidosmat viewing lense and Tessar 1:3.5 f=75mm lenses?
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Thu, 4 Oct 2007 12:21:34 -0700
----- Original Message -----
From: "Dave Hunter" <dhunter@xxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Thursday, October 04, 2007 12:14 PM
Subject: [rollei_list] Re: Diagram of Heidosmat viewing
lense and Tessar 1:3.5 f=75mm lenses?
Hi Richard:
I was able to make an aggreement with the vendor of the
Rollieflex MX
I bought off eBay a couple of weeks ago, and which turned
out to be
little more than a parts camera.
Perhaps its largest problem was the viewing lense, which
had been
etched badly by fungus....
So, this morning, I got brave or foolish (use whichever
you prefer),
removed the face, and dissassembled that lense. I was able
to clean
off the damage very carefully using a fine plastic polish
(Novus),
and the lense turned out remarkably well. Then while
re-assembling it
I ran across the bi-concave lense and noticed it is hard
to tell
which way it should be turned... Hopefully I do have it
re-assembled
correctly - that might be the only problem. However, the
end result
is a major improvement - I can actually see through the
viewfinder.
Now, comes the problem of getting the viewfinder adjusted
in synch
with the taking lense so that they both focus at the same
point....
It is all a learning curve for me, but I am used to
working on small
mechanical devices, so I kow all will work out in the
end...
Thanks for your response!
Dave
If the center element is reversed the results will be
very obvious. The image will be be fairly sharp in the
center and become blurred quickly as you move away. It will
also be quite dark away from the center.
The viewing lenses are interesting because they must form
a quite sharp image of pretty uniform quality when wide open
and have a fairly large maximum aperture. This is not
trivial for a Triplet which has just the minimum number of
variables to correct all the primary optical aberrations.
Lenses like the Triplet and Tessar are quite sensitive
to the spacing of the front and center elements: in fact
these designs are used for front-focusing lenses where the
focal length is changed by moving the front element. I
suspect that this property was made use of to adjust the
finder lenses to match taking lenses. The adjustment could
be made by slight variations of the spacer for the center
element. Since the amount of the variation would be very
small it could be done with minimal effect on the
corrections. It would be interesting to know if this was
actually done.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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