topic I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts in EF & RF Lenses

I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

JohnStansfeld — Tue, 10 May 2016 21:42:45 GMT

My EFS 17-85mm zoom lens on my EOS 40D has started to have difficulty in autofocus mode, particularly at full zoom. It hunts back and forth and is unable to focus. I dont have the problem with other lenses on the same camera so think the problem is with the lens. Does anyone have any ideas, before I have to send it away for repair?

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

kvbarkley — Tue, 10 May 2016 21:46:09 GMT

You will probably have to repair it, but is the Aperture opening all the way?

You might try to clean the contacts.

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

JohnStansfeld — Tue, 10 May 2016 21:50:47 GMT

Thanks, I am fairly sure the aperture is opening all the way. I have tried cleaning the contacts with a dry cloth and it didnt seem to make any difference.

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

kvbarkley — Wed, 11 May 2016 01:44:53 GMT

I had an issue with my 17-85, but I don't remember what it was, I think the IS died. I changed it to a 15-85 and was happy. (Until it got splashed with salt water - but it still seems to work. I am using it on my XS as a spare.)

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

ebiggs1 — Wed, 11 May 2016 12:27:32 GMT

"I have tried cleaning the contacts ... didnt seem to make any difference."

This almost never works. No surprise there. Can you try the lens on a different camera?

I am going to assume you have a situation where it would focus if it were working? Like a nice brightly lighted day out side with good contrast?

"I dont have the problem with other lenses on the same camera"

You can't compare it to your other lenses unless they are the same lens. Most likely it needs service so be prepared.

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

JohnStansfeld — Wed, 11 May 2016 12:44:16 GMT

I will be able to try the lens on a different camera next week, which should confirm where the problem is.

Yes, have tried it on a bright day, still the same problem. OK thanks for the advice re other lenses. Will use it on manual for the time being and then probably book it in for a service.

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

ebiggs1 — Wed, 11 May 2016 12:55:20 GMT

Good luck.

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

Waddizzle — Wed, 11 May 2016 13:01:32 GMT

Okay, the continoulsy hunts at full zoom lens. What about at other zoom settings, like 1/4, 1/2, 3/4 zoom? The lens has a MFD, Minimum Focusing Distance, of just over a foot, so make sure that you're at least three feet away.

Focusing is directly affected by available light, and which focusing points are in use? Does it have enough ambient light to focus? Which focus points are you currently using? Manually select just the center focus point, use "One Shot" mode, and try it again at varying focal lengths.

With multiple focus points being active, the camera will try to use the focus point that is aimed at the object closest to the camera. Sometimes the camera seems get confused as to which point it wants to use. As it hunts to lock onto one AF point A, another AF point B may seem to be better, and so it switches to Point B. As it rehunts to lock onto B, suddenly it notices A is a better choice. This can be an issue when you are in AI Focus and AI Servo modes. Turn them off, and go with "One Shot".

Check your menus, there may be a setting that controls "Lens Drive When AF Impossible". It has two settings: 0 = Continue Focus Search; 1 = Stop Focus Search. I always set that value to "1". I sometimes have the perfect storm of conditions when a lens cannot lock focus at maximum zoom, too. Sometimes, all it takes is some manual focus override, a little nudge to get it into the ballpark, and then all is well again.

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

JohnStansfeld — Wed, 11 May 2016 13:23:17 GMT

The problem is worst at full zoom, at no zoom at all it is sometimes ok, sometimes still hunts a bit.

Yes plenty of light and contrast, sunny day. Without moving the camera position and at no zoom it will autofocus OK on a contrasting subject using centre focus point only, but when I zoom in to full zoom it cannot autofocus.

Yes, just using centre foucs point on 'One Shot'.

I have found the menu for 'Lens drive when AF impossible' and changed the setting to 1 but I am afraid this hasn't made any difference.

Really appreciate your suggestions, many thanks.

Re: I have a autofocus problem with my EFS 17-85mm lens, at full zoom the lens continually hunts

Waddizzle — Wed, 11 May 2016 20:05:21 GMT

Sorry, but it sounds like the lens may need to be professionally checked out. Last call, turn off the Image Stabilization.