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Thread started 31 Oct 2016 (Monday) 19:50
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Baffling AF problem 5D MkIII

 
AdRex
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Oct 31, 2016 19:50 |  #1

Hi all, first post so please be gentle :)
I've had my trusty 5D MkIII for years & it's been pretty darn reliable & robust but recently, totally out of the blue, it's developed a weird problem.
I generally shoot in Av mode in One Shot as most of my work is of static subjects & the cam is generally tripod mounted.
AF has decided not to work through the viewfinder. Sometimes it's back-focussing, others it's totally out of focus, nothing sharp.
However... when I shoot through LiveView no problem at all. Everything works as expected.
And... it gets weirder...
Shooting with my 24-70LII zoomed to 70mm an image will be in perfect focus, at 24mm it won't focus on the selected point (tends to back-focus) but interestingly if I take progressive shots at different focal lengths the focus problems worsen as I go towards 24.
Like I said... only through viewfinder, not LV.
Anyone have any suggestions?
I hate when I have to start considering my go-to camera as being unreliable.
ps - no, haven't installed any firmware updates within the time-frame of this problem starting.




  
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rrblint
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Oct 31, 2016 23:09 |  #2

The focusing systems for viewfinder and live view are totally different systems. It sounds like you have a problem with the viewfinder system. Have you tried AF micro-adjustment?


Mark

  
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sploo
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Nov 01, 2016 07:04 |  #3

You can set an MFA value for each end of the zoom independently (and I assume it'll blend from one value to the other as you zoom). As such, if this were a new (to you) lens I'd suggest doing an MFA process at both ends (but specifically 24mm); probably using DotTune.

However, if this combo has previously been fine at 24mm, it might suggest something on the lens has worn/drifted/gotten bumped out of alignment. Unless that is, you previously had MFA values for this lens on this body and they've accidentally been deleted or changed?

On the 5D3 Liveview AF uses contrast detection - slow, but reliable in terms of accuracy. If the lens focuses fine in Liveview it would suggest a phase (viewfinder) AF calibration/MFA issue.


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scobols
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Nov 01, 2016 07:09 |  #4

That sounds like the same problem I'm having with my 5DIII (focus screen or pentaprism out of alignment).

Read this thread: https://photography-on-the.net …/showthread.php​?t=1469247

Mine is currently at CPS - I'm calling this morning to get the status. I'll update when I hear more.

Scott


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AdRex
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Nov 01, 2016 19:30 |  #5

Thanks for your input everyone. Sounding potentially very complicated.
I haven't done any checks with my other lenses but will do so to see if it's just the 24-70. Seriously hoping it's not a problem with the lens.
I treat them all with extreme care yet I've still had a couple of L-class crap-out on me in the past (but that's a whole 'nuther story relating to a 1D MkIII & Canon Australia's pathetic customer support...)




  
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davesrose
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Nov 01, 2016 20:14 as a reply to  @ AdRex's post |  #6

Since your lens works OK under LV, I'd be more inclined to think it something with your viewfinder system (like Scott's problem). Check with your other lenses to be sure, but focus screen seems like the possible culprit. Not sure what it could be if other lenses work fine. MFA just does incrimental adjusting and shouldn't be a factor for major out of focus issues.


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scobols
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Nov 04, 2016 11:55 |  #7

I just got my camera back and Canon was able to fix the problem. Here's what they had to say: https://photography-on-the.net …showthread.php?​p=18175693

Scott


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Baffling AF problem 5D MkIII
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