[Frameworks] Locked focus ring

[Scott Dorsey]

Likely the lubrication has gunked up, especially if it is a much older
lens.  If you put a couple of drops of naptha or Ronsonol around the ring
so that it can get down into the helicoil, you can probably dissolve enough
of the gunked-up grease to free it.  

It won't stay free, though... someone has to take the thing apart and 
properly lubricate it.  But you have to get it free in order to take it
apart.

If it's a good lens (ie. not a TV camera lens) it's likely worth having
a local camera repair shop do a clean and lube.  Most of those older
C-mount lenses are easy enough to work on that your local tech should
have no problem.  It's not like working on a modern zoom with a bunch
of moving elements that are all coupled together, it's just one element
moving in and out.
--scott