I was asked by a photographer to help them with setting up their newly acquired Yongnuo YN-E3-RT radio flash trigger. It’s supposed to be a clone of the Canon Speedlite Transmitter ST-E3-RT, but it has a trick that catches out the unwary.

Yongnuo YN-E3-RT - flash mayhem


I’ve been using and loving the Canon ST-E3-RT Speedlite transmitter [AFF] since it was initially launched. Recently I had tested the Phottix Laso trigger which is similar, but there’s also the lower cost Yongnuo YN-E3-RT [AFF]. It does much the same as the others, but is more cheaply constructed, however my post is a result of trouble shooting a fellow photographers setup. He was using the Yongnuo with a few Speedlite 580EX II flashes fitted with the Yongnuo YN-E3-RX receivers.

Flashes fire, but not in-sync with the shutter

The trigger appeared to trigger the slave flashes, either Canon 600EX-RT or a Speedlite 580EX II fitted to the YN-E3-RX. By that t I mean pressing the test button or taking a picture caused the slave flash to fire. However looking at the pictures there was no flash light appearing in the frame, even when the picture was of the front of the Speedlite being triggered. It looked as if the shutter and the flashes were out of sync.

FM = Flash Mayhem

The problem was found to be down to the Yongnuo’s Free Mask mode. Every time it was active the slaves would not work, in any group. Reading through the Yongnuo’s short manual eventually pointed me to the explanation of the FM icon on the triggers LCD display. When the FM icon was not shown the trigger worked as I would expect, but whenever it was present all I got was flashing lights, but nothing showing in the pictures. Taking the FM as an abbreviation my first exclamation was Flash Mayhem 🙂

Yongnuo YN-E3-RT - flash mayhem

Yongnuo YN-E3-RT showing the FM icon on the LCD

The problem is that the FM/Flash Mayhem function is not found on the Canon and Phottix triggers, so I had not realised the importance of FM in stopping the Yongnuo perform as I’d expected. It is also easy to switch the Flash Mayhem mode on without realising.

Pressing the Gr/* button for a little longer than normal switches on the FM icon, and then you are on the road to flash mayhem. If you see FM on the transmitter just turn it off by pressing and holding the Gr/* button for a couple of seconds.

Accord to the Yongnuo manual, FM should be possible to use with Group mode only, but it can be switched on in other modes were flash groups are used, including E-TTL, Manual and Multi flash. I found that in any mode it makes the slave flashes fire out of sync with the camera shutter.

Yongnuo legacy mode for non-Canon cameras

Not to be totally down on the Yongnuo, I might actually have a use for one of it’s extended functions. Legacy mode can be used with manual flash power settings to allow non-Canon camera systems to trigger Canon flashes over radio. So when I’m running a workshop on lighting with small flashes then the Nikon, Sony and other cameras can trigger my Canon radio flashes in manual mode, and set the power from the YN-E3-RT.



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About the author

Full-time photo tutor and photographer. I love to share my knowledge and skills to make photos, videos and teach others. I write books and articles for photo magazines and I always have at least one Speedlite flash in my camera bag