I recently used this lens with an extension tube to photograph some birds and noticed that the lens has become "loose" in the middle. The back one third (approx) of the lens can be moved slightly off axis with the front two thirds of the lens. This appears to be a possible looseness with the focusing mechanism. The rear part that has this movement doesn't contain any optics.
Any idea what is involved in this repair? Is it a simple adjustment or is the repair more involved than that? Thanks for any help you can provide. Tom Reese
