600RT Flash bug in new Canon 5DIII firmware.

Started May 12, 2013 | Discussions thread
Zeee Forum Pro • Posts: 16,828
Re: 600RT Flash bug in new Canon 5DIII firmware.

Rafael Fischer wrote:


I have found a bug in Canon's new firmware. Need more testers.

I have 2 Canon 5D3 Flashes. One was from March 2012, and the other December 2012 (so they are not the same batch)

I have two 600RT, one 2 months older then the other.

I used the 600RT and the two 5D bodies for 4 months, no problems over 40,000 shots taken. Updated to the new firmware last week.

I noticed my flash did not fire 100% as it had prior. Not as if was not accurate, as in DID NOT FIRE PERIOD. 4 different sets of battery, changed lenses, changed 600RT from camera to camera, same issue.

It can be made worst by putting the camera is HS sync. I found if I put my camera on HS sync, then turn the exposure down, the 1st 1 or 2 shots, the flash does not fire. The EXIF says "NO FLASH" as if it is no on the camera.

NOTE: It is NOT low battery, or the batter NOT recycling. 1st, they are flesh, 2nd, I was testing at ISO 6400 10 feet from a wall 3rd, some of the test where 10 seconds from flash to flash.

It will still do it even when not using HS sync, but it is more like 1 in 10-20 shots. (I am not shooting rapid fire, and like I said, shooting at ISO 6400, which means the flash is using very little of its full power..

Here is the where the BUG is. When you put the camera in manual focus, OR turn off the IR, it works fine.

What it appears has happened, is when Canon updated the IR, since it was slowing down focus, it created a bug.

I need someone else to verify this since I only have 2 5D3 and 2 600RT. So if anyone out there has a 5D3 and a 600RT, contact me. ESP if you have NOT updated the firmware.

There is no workaround, and it does this even when the cameras are radio slaved to each other.


I have posted a topic some days ago with similar problem just because i haven´t found yours!

I´m having the exact same issue with my 5D3 + 600EX-RT. But with me, the case wasn´t too severe, i have roughly a 3-5% os misfires on a entire wedding (about 1.200 shoots).

All my gig is brand new and when i received the câmera, updated the firmware on the same day. My business parter have a 5D3 too, but she shoots only with 580EXII and the problem didn´t show up…

Thanks for you testings and pacience to explain the issue and results, now, we need just to wait Canon fix it on a future update

So you are saying the camera will release the shutter but the flash will not fire or both flash and shutter will not activate?

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