Canon Serenar 85mm f2

The focus action on the lens should not be so stiff as to cause it to unscrew. If it is that stuff, a Lube job is probably required. I use this lens on my M8 with an LTM to M-Mount adapter. I "cheated" and worked a little sewing machine oil into mine. When received, it was very stiff.

 

Yeah I had to work on my jupiter to avoid it unscrewing from the adapter when focusing. Its fine now.
Mac you got a pic/link to the serenar Canon? It must be from the Canon rangefinders right?

 

Sering machine oil is light, maybe a little more refined than shredder oil. Look in the back of the focus mount, with the camera at closest focus. Seems to me a couple of drops of oil into the mechanism at that point could be worked in while moving from 3ft to infinity.

 

I checked mine- and that is how I worked the oil in. Set the lens to min focus, look at the rear. There is a cut-out section that exposed the back of the helical. Drop some oil a little at a time and then work the mechanism.