Quote Originally Posted by Mark J View Post
I think that the rear asphere in these is correcting a lot of aberration from the front group. Hence the tolerance in positioning of the two sections relative to each other is likely much tighter than some earlier lenses.

Yes T.C. I can believe that the lens shims are thin, might be a 'thou' or slightly more, to make a useful step in the air gap.
I spoke to Schneider about my Componon-S 210 a few weeks ago and they warned me to look out for a shim when I took it apart to alter the mount. It didn't have one, but they said some have one, some don't.
In addition to the examples of new lenses, shimmed and not, that I cited above, I did find a used 55 mm Apo-Grandagon to have a shim .012 inches (about 0.3 mm) thick (measured with dial calipers.) . The shim on my 120 mm Super Symmar HM seemed rather thinner, delicate to the point I'd rather not risk handling and measuring it.

David