EF-S 17-85mm f/4-5.6 IS USM Focus moves erratically but can't lock in

[timtom64]

Hello all.  Suddenly, whenever put into auto-focus mode, this zoom seems to go a bit crazy as it erratically attempts to focus on something, but it cannot.  It just keeps moving erratically but never finds a home.  Does anyone have trouble-shooting suggestions?  Thank in advance!

[Tronhard]

Hi and welcome to the forum:
Can you offer some more detail please?
What camera are you using this with?
Has anything at all changed with the camera recently?
What kinds of objects are you attempting to focus on and is that different from previously?
What shooting mode - Av, Tv M etc., are you shooting in?

[stevet1]

timtom64,

Does this happen with any other lens, or just this one?

Steve Thomas

[ebiggs1]

More info is probably not needed and about the only troubleshooting thing you can do is a full reset of your camera. Hope it is misbehaving. You can try the lens on a different camera, too. Try other lenses on the offending camera/lens combo.

Remember the lens does not focus. The camera tells the lens when it is in focus. If you don't know how to do the full reset consult your manual. Do that first.

[timtom64]

Hi Trevor.  Thanks for your reply.  I was using it on an 80D, and nothing much has changed.  The problem pops up no matter what I try to focus on.  And the problem persists no matter what shooting mode I'm in.

[timtom64]

Hi Steve. All of my other lenses still work perfectly. Thanks for your reply.

[timtom64]

I will try this lens on another body but I'm not optimistic because my other lens work fine on my 80D.  I just purchased an R6, and I bought the adapter, so I'll give that a shot pretty soon.  I hear you about the lens doesn't focus.  I'm thinking maybe it could be dirty contacts?  It makes sense for me look into the best way to clean the lens contacts.  Thanks for your reply.    

[ebiggs1]

"I will try this lens on another body but I'm not optimistic ..."

I hear ya but these things are all you can do to troubleshoot. At least it makes you feel better thinking you did something. I don't know how old your particular lens is but it is a very old design around 20 years or so. You can look for a good used one as they aren't expensive. The EF-S 17–85mm was a step up in IQ along with build quality and focal range compared to the standard kit lens EF-S 18–55mm lens

[timtom64 · Accepted solution]

OK THIS JUST IN.........      I let the camera sit face down without a lens or battery for almost a week, and now it seems to work just fine!  Yay!  Very stoked.  Thanks for your help, everyone.  And to anyone else who encounters the same problem, open that camera up and let it sit and dry and know.....   THERE IS HOPE!!

[crumhorn]

Did you purchase this lens as a refurb or used?

I bought this lens used about a month and a half ago. Verified no damaged by the photos and the seller claimed it was fully functional. When I received it, the lens was a good shape with no issues with the glass. I tested it out very briefly for a couple of days and saw the erratic issue with the AF. Both times I was inside with the first shooting outside the window. But on the third day I took it outside and the AF worked flawlessly every time. I must have focused 300-400 times and every time it worked. And I haven’t had an issue since. I wondered if using it inside the house was the issue with indoor lighting but so far the issue has not returned, even if shooting inside. So, do you have this issue regardless of being inside or out?