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Sudden autofocus problem on 5D Mark III


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.



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?



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