How to Unlock 1/320s Flash Sync on the Canon R5 Mark II

For underwater photographers, maximum flash sync speed is one of the most important camera specifications, and I recently discovered that the Canon R5 Mark II can sync a strobe at up to 1/320s in full resolution mode (no crop)!

Why is maximum sync speed so important in underwater photography?

When using strobes underwater, our number one goal is to get the strobe’s white light to overpower the ambient blue light, restoring warm colours to our images. This can be challenging in shallow water under bright conditions, where ambient light levels are high.

The solution is to increase your shutter speed, as this reduces ambient light without affecting the strobe’s contribution to the exposure. Unfortunately, there is a limit to how fast your shutter speed can be when using strobes. This limit is called the maximum sync speed, or X-sync speed, and it varies from camera to camera.

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How to set up your R5 Mark II to synchronise with strobes at up to 1/320s

By default, the Canon R5 Mark II already offers a respectable 1/250s X-sync speed when configured in Electronic 1st Curtain Shutter mode (see my Canon R5 Mark II underwater setup guide for full details on how I’ve configured my camera for underwater use).

To unlock 1/320s, navigate to the camera’s Shooting Menu (red menu), enter the External Speedlite Control settings, scroll down to Sync Speed Priority, and turn it ON. That’s it!

You need a compatible flash trigger though (see below), otherwise that option may not be offered, or it will be available but you’ll find portions of your images aren’t lit by your strobes.

Why am I only finding out about this now?

If you look at the R5 Mark II’s manual, Canon states that the Sync Speed Priority option only works with select Canon flashes and warns of possible underexposure, without providing much additional detail. That’s why I initially gave this option a pass when familiarising myself with the camera, when writing my underwater review of the Canon R5II.

However, while testing the TRT-Electronics eTurtle Smart3 TTL flash trigger for Canon mirrorless cameras (the review is coming next month), I decided to give it a try. To my surprise, it worked perfectly.

Flash trigger compatibility

Some flash triggers won’t even reach the camera’s standard sync speed. This isn’t a Canon-specific issue—I have tested triggers for other camera brands that also fell short of achieving the camera’s maximum sync speed. I think this speaks to the challenge of designing flash triggers in general.

So, when I reviewed the eTurtle Smart3 Manual trigger for Canon, I was already pleased to see it could reliably reach 1/250^th, while supporting fast burst rates and delivering excellent battery life. I certainly wasn’t expecting it to go even further.

Since then, I have verified that both the Manual and TTL versions of the eTurtle Smart3 trigger are compatible with the Sync Speed Priority option, and I haven’t noticed any downside to using that shutter speed, whether that’s with the Retra Pro Max II or Backscatter HF-1 strobes.

Conclusion – A Seriously Good News for Canon RF Shooters

In today’s mirrorless and DSLR market, fast synching cameras are expensive to get! Most cameras in that space have a X-sync speed of 1/200^th or 1/250^th, with only 3 cameras going faster than 1/320^th.

These are the Sony A1 and A1 II (1/400s sync speed) and the Sony A9 III (effectively unlimited sync speed thanks to its global shutter, albeit with some dynamic range trade-offs). However, those cameras come at a significant premium. A Sony A1 II will set you back around USD 7,000, and an A9 III approximately USD 6,800, whereas the Canon R5 Mark II has a much more approachable asking price of around USD 4,400.

While I have only tested the eTurtle Smart3 triggers with the Canon R5 Mark II, I strongly suspect the same 1/320s sync speed can be achieved with the recently released Canon R6 Mark III too, as it also features the same Sync Speed Priority setting in its menus. Hopefully, future Canon RF cameras will support this synchronisation speed as well.

About the reviewer

Nicolas Remy is an Australia-based pro shooter and founder of online underwater photography school and community, The Underwater Club, with members in 26 countries. He serves as an ambassador for Mares and Nauticam, and chairs the jury of the prestigious DPG Masters photo competition. Nicolas’ images have been widely published in print and digital media, and have won over 40 international photo awards. To see more of Nicolas’ work, visit: www.nicolaslenaremy.com.