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Canon radio-controlled flashes failing in use - Senders and receivers disconnecting



I am spreading the news about the failure of communication between Canon "Sender" (Master) flashes and Canon "Receiver" (Slave) flashes.  Since around 2020 the communication between Master and Slave flashes can be broken by a public radio wave of some kind.  I’m not an EE, so I can’t tell you what the source of the problem is, but I can tell you that I have tested equipment all over the greater Seattle area, and about 80% of the time the Slaves disconnect from the Master in under 20 minutes of being turned on.   The shortest time to disconnect happens in 60 seconds with most disconnects occuring in 8-12 minutes.  I’ve only tested this in the greater Seattle area, but I suspect that if you are in a major urban area you will experience this failure.

I’ve tested this with Canon 600EX RTs and with a new R3, RL-5, and ST-E10, so it’s happening to the latest Canon equipment. 

You can read about what I’ve tested here:




Can you take a trip to somewhere far away from the Seattle area and see what happens?

Have you spoken to any other photographers with Canon flash gear to see what their experience is?

If it's 5G radiation doing it, it's hard to believe there isn't more of this happening all over the country.

It is happening everywhere.  It also happened to me and is the reason I have since moved on to a different brand for my lighting.

There are several threads on these forums detailing the experiences of others.  i.e. that for some unknown reason, communication links between triggers (doesn't matter if its the first or second-gen ST-E3-RT) and the flashes will intermittently fail (first and second-gen 600 EX RTs, etc.)

Some of the threads:

In that last one, I had replied in 2021 that I had not yet experienced the issue.  But soon thereafter, I began to experience it.

There's hope that Version 3 of the ST-E3-RT will address the issue.


Camera: EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L
Lighting: Profoto Lights & Modifiers

I found the User Manual for the new ST-E3-RT (Ver. 3) on one of Canon's international websites. With only some minor changes the manuals for the Ver. 2 and Ver. 3 triggers are identical. Most importantly, in the specifications section I found that the radio systems appear unchanged.

Frequency:  2405 - 2475 MHz
Modulation System: Primary modulation: OQPSK; Secondary modulation: DS-SS
Channel: Auto, 1 - 15
Wireless Radio ID: 0000 - 9999

So, it seems unlikely the new ST-E3-RT (Ver. 3) trigger will solve the dropped linked Wi-Fi issues with the RT system that many users are experiencing and reporting in this forum unless there is some change to the FW that automatically resets the link if the flashes and triggers disconnect. I am not hopeful. 




Thanks for the info on the ST-E3-RT (V3)   Disappointing, but not surprising.   I kind of figured given that the EL-5 and EL-1 also fail this very basic proceedure.

Yes - a change in fw would be about the only thing to fix it.  The 5gig band is full of signals and not likely to quiet down any time soon.  

When you get away from urban areas they work 95% of the time.  I just don't get paid to shoot in those area.  Also see RS-EOS comment about other photographers.

It is happening everywhere.  Read on...   


I read your note here and also went to your website to read your detailed testing report. Well done testing and write-up.

I sure wish someone at Canon would weigh in on this issue. As it is, one can only conclude that the Canon RT flash trigger system is not suitable for its intended use in its current form based on the many link failures reported here in their own forum.


Couldn't agree more.  I really can't believe they are knowing selling equipment that is prone to failure.  I'm hoping a firmware update could fix the problem.