Lens problem. Help!

Few months ago I noticed that my Canon 17-55mm lens could not focus. When I half-pressed the shutter button, the lens was like shaking back and forth to try to get a focus but it never got it. Then after a while when I put it on, it's working normally. After a while, the problem resumed. Until now. It's working fine now.

Do you have any idea about this kind of cases?

Try it outside in daylight with a good contrast in the view finder. when you tried, the camera was probably having difficulty to auto focus in a dark/low contrast view.

I had a problem with my 100-400mm lens that sounds similar. I sent to Canon to repair and it needed a new focusing unit.

Thanks! Lately it's focusing alright most of the time. The success rate is much higher if I turn off the IS. I'll try to wait until it's completely non-functioning.

I fell holding my camera with the 17-55 attached and the lens would not focus, acted a bit like you described. Camera and lens are at Canon Irvine getting repaired and cleaned. The flat rate price for the lens repair was $95.00. You might want to consider sending it in for a checkup.

$95 sounds right. Well, then let me do it when I have time later this week. Thanks a lot!

Speaking of fall, I might have one incidence like that. But it's almost a year ago.

Sorry to revive this thread. The problem had been gone for a while and therefore I hadn't sent the lens for repair. But then, today something happened that made me wonder what the problem really was.

I was using the 17-55mm on my 7D and today there were occasionally error messages (communication between the lens and the body is faulty. Clean the lens contact) when I tried to take pictures. In order not to miss the moment, I changed the lens to a manual-focus Takuma 50mm. But then even that manual lens had the same error message! The adapter is AF-confirming but the body detected nothing. When I changed back to 17-55mm, I could take some pictures, though occasionally the error appeared.

So, would it be the body that has the problem? But in the past 3 months I've been using it with either 17-55mm or 70-200mm. Especially for the latter, I have never run into this problem. If I should send something to Canon for checkup, should it be the 17-55mm or the 7D body?