5D Mk III Focusing Issue

[tjlawler]

I have been using my 5D Mk III for a few weeks now.  Overall I am very pleased with the photos.  One quirk I have not figured out is that the camera often will not focus as I switch between focusing limits.  To get it to focus I have to do a quick manual focus (just turn the focus ring while still in AF) and now focus will occur with no problems.  This happens with both my 300 f/2.8 and 500/f 4  lens with the 1.4 extender attached.  I have not tried this without the extender attached.  Did I do something to mess up some setting in the AF in the camera?  I am using center spot focus.

Thanks for any assistance,

Tom

[CW Aust.]

Try the fourth purple focusing menu screen,top item "set drive when AF impossible" should be set to on.

[CharlieB]

My own experience was the same with the 5D2 and 7D.... and it happened with almost every lens I own ( which is 9, including four L's ).  In both cases, I had focus turn itself off even while attempts were made to focus on good contrasty and well lit subjects.  In both cases, rotating the lens in its mount a few times permanently fixed the problem.

I'd have put money on clean lens contacts - they all worked well with my older bodies EOS 350 and EOS 400.  Having all the lenses behave the same way... makes me think camera body issues.  Having both bodies have the same issue is beyond  my thinking.

So, I have to idea what the issue was.  Never made an adjustment.  After a few partial dismounts - via rotation - the lenses all worked perfectly on either body.

A "go figure" moment for sure.

[tjlawler]

At first try the suggestion "set drive when AF impossible" to on appears to solve the issue.  Funny...I think I have this set to off on my 7D. 

Thank you so much and I will certainly find out today if this solves the issue since the camera will get a good workout.

Tom

[awinphoto]

My 7d and 5d3 do this on occasion with my 70-200 every so often if it's at the MFD and my subject is at the other extreme, or visa versa...  Since my other lenses AF alright, i'm thinking it's a lens issue or lens communication issue...

[JMeneses]

Thank you CW Aust. I had the same problem and now is fixed.

[apersson850]

Since my other lenses AF alright, i'm thinking it's a lens issue or lens communication issue...

It doesn't have to be. It depends on the depth of field for the lenses you use. A longer focal length and/or larger max aperture will suffer more from AF drive when focusing is impossible being set to off than a slow wide angle lens will.