No! It isn't the camera. I have tried the lens on a Canon 7D of my own, a Canon 50D mine. Also my friend's 7D & it works just as badly on them all. So it is the lens auto-focus that is not working properly. I use the lens to photograph flying birds so it is essential that the AF works fast & is accurate. I think I am resigned to the fact that I either have to pay a fortune to have it repaired or buy a new one.
You wouldn't have to pay to have it repaired, if it were still within the warranty period.
Maybe I asked this before, but was the lens ever operated in a gritty sandy or dusty environment ?
No again.It is quite an old lens. January 2006 it was manufactured. It has had a great deal of use since then. Thanks for your advice but I think I will first try to get it repaired - if the cost is reasonable. If not I will have to replace. Cheers.
Cheers XXXXX XXXXX is a great help. I wasn't too sure where to contact Canon Services. I have a friend who has used them for repairs, but he is away in South America for a few weeks. I'll have a proper look tomorrow. Glad I contacted you. If there is any way I can tell Justanswer that I am very satisfied with your help I will do.