I have a Tonika AT-X 400mm lens that i brought off a friend for my D50 who was a pro photographer. When i brought it he did say that i might experience which at first for the use it had was a minor annoyance and today became more than that in the lens gives me an error on the camera after being left doing nothing for too long. Now if i remove the lens and put it back on it is fine. Now my friend did say i could get it re-chipped or something along those lines. I just wondered if anyone has any information about it!