Originally posted by tom1803
The F 70-210 is a little bit trickier to take apart than other similar F series lens.
Also, as with all A series lens and forward, if you take the mounting flange off, there are many small parts that are spring loaded, easily lost and very fiddly to put back together again.
Here's a photo of the F70-210, ready to put the mount back on. The mount has individual plastic insulators for each contact. Other lenses are made so it's much easier to align all these contacts, springs and insulators as a group, but this lens takes a lot of patience to get all the loose parts in place.
The front lens group does come off easily. You could possibly avoid taking off the mount by removing only the light shield, a plastic part inside the mount that closes the gap between mount and the rear lens element. The rear lens group can probably be unscrewed with the light shield out of the way. The hair is probably between the inner element of one of these groups and the aperture blades.
I think $50 is kind of high. I just sold one of these for $50 with some light scratches on the outer edge of the front element. I'll sell you one with element separation for $40.