I have seen two APM/TMB 100mm F8 that pinched in
sub-freezing weather. One was under APM warrantee
and Markus had the cell re-machined in Germany
at no charge, and made a new interferogram.
Took about 1 month with shipping, etc. It works
perfectly now with no hint of pinching to at
least 16F. It is probably the best refractor lens
I have ever seen, including about 2 dozen high-end APOs.
It was well-worth the extra trouble.
I think if
you contact Markus directly, he will be more than
happy to work with you. My experience was certainly
first-rate. I suppose if LZOS or LOMO has given him
a bad batch, it will take some patience to resolve
everything.
The other lens was an official "TMB" where the warrantee
was a few weeks past expiration. Thomas was suprisingly
unhelpful, was unwilling (or unable) to even check the
lens, and quoted price for repair that was most of the
cost of a new lens. :C Granted it was out-of-warrantee,
but I expected better.
The problem seems to be that the ID of the cell
is machined a little too small by some microscopic
amount. I think they make the lens cell tight-fitting
to keep the elements aligned, but sometimes it is
a little too tight. The elements are supposed to
float up and down in the cell against the mild force
a spring cut into the retaining ring. But if the
cell ID squeezes the glass from the sides, all the
floatation stops and they pinch.
As a fellow amateur astronomer my heart goes out to you. I had an APM/TMB 80mm triplet also---same problem.