Sudden autofocus problem on 5D Mark III

[sdhweb]

Hello, I have a nearly two years old 5D Mark III with only 7800 images taken. The camera has been working well and I've been happy until now.

Yesterday I experienced that autofocus would not work on an easy target. I thought 'what the heck is going on?'... After that incident I keep having this problem. Sometimes autofocus seems to work and sometimes it seems to do nothing at all. The focus confirmation light and the AF status indicator is just flashing.

I use the AF-ON button for focus and the IS is leaping to action but the autofocus doesn't seem to be doing anything. I experience this on contrasty subjects in full daylight. And suddenly it may be working again but it seems very unstable. I haven't done any changes to the settings before this started to happen.

It seems to be worse when I change back and forth between focusing on something close and something far away. If I manually adjust the lense very much out of focus it seems to have a very hard time to get back on track. Mostly it fails. If I then help it quite a bit and manually adjust the lense more in focus it suddenly works again.

I've always had the setting 'Lense drive when AF impossible' set to OFF and I've never had these problems before. Changing this setting to ON seems to 'help' a little, it at least changes the behaviour of the autofocus. With this enabled in seems to at least be trying (and more often succeed) instead of just doing nothing. Keep in mind that I'm talking about good and easy autofocusing conditions here, not low light situations.

Conciderations:

1. I have tried two different lenses with the same result (EF 70-200 F4L IS USM and the EF 100 F2,8L IS macro)

2. I have cleaned the lense contacts on both the body and the lense.

3. I've upgraded from firmware 1.2.3 to 1.3.3 and reset the camera to factory settings.

4. I've changed focus back to the shutter button

None of the above actions have made any difference to the situation. I've had this camera for nearly two years and something has definitely happened. The camera is very well treated and have no visible damages.

Any advice on this one?

[TCampbell]

Which focus type are you using? (Spot, single point, expanded area, surround, zone, or full 61 point auto-select?)

Which focus mode are you using? (One-shot, ai-focus, or a I-servo?)

[sdhweb]

Ahh, I forgot to write that this happens in both One shot and AI servo (AI focus not tested). I've always used the center focus point alone.

[Peter]

Dust at the AF sensor is also possible. It sits under the mirror.

[sdhweb]

Hi,

Thanks for the response. I've tried to clean it by using a blower with the mirror up, but it looks very clean inside. After the cleaning I took about 1000-1500 images, mostly of flying seagulls and thought the autofocus was OK. But right before it was time to go home it failed again. I had just focused on a stone 2 meters away, and then when I tried to focus on the mountains in a distance it just fails. It cannot focus. There is plenty of light and contrast.

I have done the same test several times during todays testing and it worked every time so I really thought the cleaning did the job. But failure again right before I was going home 😞

So I guess I need to send it in for repairs...

[JonKline]

Any time I have any Canon issues, I don't hesitate to send it in for repairs. Unlike certain other camera brands that start with N, Canon's turn around time for repairs is WAY faster. Usually it's less than a week to get everything back to 100%

[sdhweb]

I hope you are right JonKline. I live in Norway so it may be different here, not sure. I think we have less options/shops to choose from since we are a much smaller country.

The worst thing that can happen, that I fear, is that they'll send it back and say they don't find any errors. Hope that not happens because something i clearly wrong.

[sdhweb]

Hi all, I'm sorry for the late reply here. It took the shop over 4 weeks from they received the camera till they actually started working on it. They blamed it on summer vacation 😉

It only took them a day to repair though once started. The AF-sensor had gotten shifted out of it's calibrated position (no clue how that happened) and it had to be recalibrated and then the AF had to be adjusted. They said the camera needs to be impacted for the sensor to 'move'. I don't know how this may have happened since I'm very careful with my gear, but I'm glad the problem is fixed 🙂 Thanks

[sdhweb]

Hello again, one more question here if I may... My camera has worked well since the repair but today I tried to shoot some macro which I haven't done in a year or so.

Is it normal that the camera cannot focus on something 'further' away right after I've focused on something very close? I've hold the camera very close to for example a flower and focused on it. Then I move the camera and point at my foot which is 1 meter away. When I look in the viewfinder it's all very blurry because it's out of focus. Nothing strange with that but the camera is not able to focus, even on normal contrast subjects.

Is this because the focus is so much to the macro end that it's hard to find subjects in a more normal distance? Or is it my camera again? (If I help the camera and focus manually till it's almost in focus then autofocus find focus again.)

The lens I used was EF 100mm f/2.8L IS USM

[ed_vatza]

First check the obvious. I believe you have a control on the lens that lets you select focus range. It goes from 

1' (.3m) - 1.6' (.5m)
1.6' (.5m) - ∞
1' (.3m) - ∞

Make sure it is not on the 

1' (.3m) - 1.6' (.5m)

or you won't be able to focus on your foot.

Easy to forget to switch it after using in a extreme closeup situation.

Ed