Canon 28-135 or 40D occasional focusing problem: I have a 40D with an occasional problem with focusing. About 1 time in 10 the camera refuses to focus. It may hunt back and forth or...

wkocken Loc: McGregor, MN

I have a 40D with an occasional problem with focusing. About 1 time in 10 the camera refuses to focus. It may hunt back and forth or not even attempt to focus. It doesn't seem related to any particular type of subject or distance. I've removed the lens and reattached it, turned the camera off and on, switched in and out of manual focus. None of these seem to fix the problem. I always use just the center focusing point in single shot focusing mode.
I think I sometimes have the same problem with my Tokina 12-24 lens, but I don't use that lens much, so I'm not sure.
Does anyone in this group have experience with this problem. What are the causes and solutions?

donrent Loc: Punta Gorda , Fl

Did you clean the contacts on lens and camera ? Q-tip dipped in Alcohol is best... I had the same prob once and cleaning fixed it instancely...

jimmya Loc: Phoenix

wkocken wrote:

I have a 40D with an occasional problem with focus... (show quote)

How much available light do you have in these situations? If the lens can't see enough brightness & contrast it can't focus... could be the problem.

wkocken Loc: McGregor, MN

This is in broad daylight and happens with both high and low contrast situations. Previously, I had no issues with the ability to focus. It suddenly started to happen while on vacation.

I have read elsewhere that it could be caused by dust/dirt covering (part of?) the focus sensor. Has anyone ever heard of this issue?

I have not had a chance to clean the contacts, although they look very clean to the eye.

jimmya Loc: Phoenix

wkocken wrote:

This is in broad daylight and happens with both high and low contrast situations. Previously, I had no issues with the ability to focus. It suddenly started to happen while on vacation.

I have read elsewhere that it could be caused by dust/dirt covering (part of?) the focus sensor. Has anyone ever heard of this issue?

I have not had a chance to clean the contacts, although they look very clean to the eye.

If it's occasional I'd say it's not the contacts. Could be dirt on the focus sensor or could be an intermittent problem with the camera or the lens.
Difficult to say unless you talk with Canon and possibly have the camera gone through for a tune up.

It also might help both you and Canon to know the shutter count. That's like millage on a car. You can't get that through normal exif data but a free download from EOSInfo might do it. It works with my XS and my
t1i.

Good Luck

wkocken Loc: McGregor, MN

Well, cleaning the contacts didn't help. I also tried turning on all of the focus points, instead of just the middle one. That didn't work either. I think the next step is to send it in. I still need to verify if it is happening with just this lens or if it happens with multiple lenses. That would identify the source of the problem
I don't think it's shutter count, but I'll check it anyway.

jimmya Loc: Phoenix

wkocken wrote:

Well, cleaning the contacts didn't help. I also tried turning on all of the focus points, instead of just the middle one. That didn't work either. I think the next step is to send it in. I still need to verify if it is happening with just this lens or if it happens with multiple lenses. That would identify the source of the problem
I don't think it's shutter count, but I'll check it anyway.

You turned off all the focus points? That gave your camera nothing to guide it to focus. Try the single point dead center. If that doesn't work yes it's probably the lens. As you suggested try other lenses and you'll know.

It may be time for that lens to have a tune up or perhaps replaced if it's new.

Good luck

wkocken Loc: McGregor, MN

Jimmy,
I normally use just the center focus point. When I turned on ALL of the focus points, the problem persisted.
My next step is to do some testing with my 70-300 lens.

jimmya Loc: Phoenix

wkocken wrote:

Jimmy,
I normally use just the center focus point. When I turned on ALL of the focus points, the problem persisted.
My next step is to do some testing with my 70-300 lens.

That would be a good thing. I see, in your last post I didn't read about the single point - that's what I use all the time and have very good luck with it.

I have this same problem with a Tamron lens that I own - focus problems.
It works fine in bright sun but anything else and it wonders all over the place trying to focus and usually doesn't find it - go figure.

I still believe that, unless your focus sensor in the camera is dusty or dirty, that it's the lens. Please let me know your results with the 300, I'd be interested in hearing what you find out.

Good luck

Jim