problem with AF on 17-40 F/4L

Hello potn'ers.

Just today my 17-40 started doing funny things when I tried to focus in what was definitely sufficient light. In short, the AF does rotate, but wildly to infinity and back, settling on a position that is decidedly NOT in focus. I've cleaned the contact to eliminate electrical issues. I've tried another lens on the camera to eliminate the camera as the issue. I've also tried manually focusing the lens and looking for the red focus light to light up appropriately--it does.

I should also add that I'm in One-Shot shooting mode, though it acts sort of like it's in a servo mode.

Has anyone seen this issue ? Is is something that is in the realm of possibility in terms of a self-fix (even if it means taking it apart). If it's due for a fix at Canon, has anyone had a similar repair done on the lens and can guestimate what the cost might be ?

Thanks for any suggestions, last rites, etc..

Strange. Tried again today and it wasn't working; then zoomed in and out trying focusing at different zooms. Now it seems to have 'locked in' again and is focusing normally. It also sounds normal again when it's focusing.

It's very possible i'm imagining a difference in the way the lens feels, but it does sort of feel like the assembly inside isn't quite stable--like it is moving laterally back and forth. Like a tiny clunk inside when I rotate the orientation of the lens. I also find it strange that when I look into the back of the lens when the cap is off, I can see, depending on how it is zoomed, around the last lens element and into the assembly (e.g. I see a ribbon). Perhaps it's supposed to be like this and I've just never inspected it before.

Anyhow--I still don't trust the lens. Any suggestions ?

Odd, if you sort this out could you report back on what you find?

hey, Rick. I still haven't sorted this out yet. I took it to Vistek (one of the top two photography shops in Canada) and to a repair shop. Both agreed with my troubleshooting methods. Moist contacts was suggested by the guy at Vistek. The other place thought it may have been an aperture problem (sticking at f/8 e.g. would affect the AF ability due to decrease in light passing through). I hadn't thought of that and so will look out for errant exposures in the future.

I'm still puzzled though, and am super paranoid the lens will fail again soon.

Ah. One more thought. What was different the day before the lens' AF failed was that I was shooting long exposures very near to waterfalls. Though no water directly got on the lens it's possible that the moist atmosphere affected the contacts at least temporarily.

To get moisture on the contacts, you must have changed lenses at the waterfall.
The 17-40 has a rubber gasket for weather sealing, were you using a filter on the front ?

finally what was the issue ? I have the same problem