In article , radiojohn@delphi.com says...
>I finally bought a 210MM Symmar (spelling?) that is convertable.
>Can you explain which element goes where?

I think you leave the rear alone and unscrew the front set of elements
from the shutter to nearly double the focal-length. (Be careful not
to cross-thread the fine threads when replacing the front half.) Use the
second (slower) set of apertures when the front is removed (you will need
much more bellows extension for correct focus), and use small stops.
(Since only 1/2 of the optics remain, the simpler lens is less sharp.)
Using a yellow or stronger filter may improve sharpness with B & W film.
Hope this helps.