EF 28-135 focusing issues?

[btaylor]

If it's an intermittent issue it could be an issue with the contacts between the lens and the camera body, it happened to me once a while ago with my old 28-135 and still does occasionally with the 24-70mm.

Try giving the contacts a clean with a soft cloth to remove any grime or corrosion and see if that helps.

Ben

[jrw]

One other item to check is whether the lens can rotate slightly when in the locked position on the body. I once bought a new lens that apparently had a slightly wide slot where the locking pin fits. I figured out that it would work flawlessly when I kept the lens fully rotated in one direction, but not the other. Exchanged it for another and have since had no problems.

If you have rubbed the contact surfaces with your fingers it can transfer some oil from your skin onto them. Having oily skin myself I have learned to be very careful when handling lenses. If the dry cloth doesn't work, try moistening it with a very small amount of alcohol to lift anything on them. Do not ever try using an eraser on them. Some sites still recommend this old practice, but it is a bad thing to do. It can wear away the gold plating which will make the problem much worse, to the point that the lens can become virtually unusable.