5d Mark 3 Fail

I have been experiencing a phenomena with my 5D Mark iii and wanted to see if anyone else have had this issue. I have sent both my camera in as well as my flash and Canon said nothing is wrong. I shot a quick video this morning showing my issue then called canon tech support in Virginia and to my surprise this issue was being duplicated by the tech.
In a nutshell My camera is all in Manual except for the focus and I am using either my 580EX2 flash or the 600EX-RT flash on ETTL directly mounted to the hot shoe. After taking a photo (typically happens when over 800 iso) I wait for about a second or two after the green confirmation light turns off and the take another photo. The Auto focus assist light turns on, the camera locks focus and takes the photo, however the flash fails to fire. It seems to only happen when in auto focus and I manually select the ISO. If I use it in manual focus or in auto ISO select this issue does not appear.
The tech at canon has no idea why it does this because he also tried it on the 7D as well as the 70D and the flash fired each time. The issue only happens on the 5D Mark 2 and 3. It happens more often when in a dimly lit room as opposed to a bright room. Not sure if it is related, but my issues started on my Mark3 only after I updated the firmware 5 months ago or so.

Please let me know if anyone else has experienced this problem and what they did to fix it.

https://www.youtube.com/edit?o=U&ns=1&video_id=n_Yzq0oQCtc
 
Oct 22, 2013
3
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I have tried to reproduce the phenomena in exactly the same setup as yours but the flash fires as every time as it should.
 

Rob Carter

I'm New Here
Oct 21, 2013
13
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I have had exactly the same fault with a 5D3 but it never occurred with a 5D2. It happens using a 580ex or a 580ex11. I have tried all sorts in the menus but have not found what causes it. I was coming to the conclusion there was a fault in the camera and was about to send it off to Canon.
 
Oct 22, 2013
3
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Just tried to reproduce it again, this time with a 580EXII. Same result, flash never fails. So, 5D MkIII with latest firmware and 600EX-RT or 580EX II no flash problems like you are experiencing.
 
loetleen said:
Just tried to reproduce it again, this time with a 580EXII. Same result, flash never fails. So, 5D MkIII with latest firmware and 600EX-RT or 580EX II no flash problems like you are experiencing.

Is your ISO set manually? Typically it seems to fail more at higher ISO's. Also, my flash is set to ETTL, camera is set to manual shutter as well as f-stop and the auto focus is ON. Take a picture (in a dimly lit room), Wait about 1-5 seconds after the green confirmation light goes out. This is when I experience the problem.
 
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