How many shots are you trying to fire off at a time. Are you remotely triggering the camera also what speedlite are you using Canon or 3rd Party. Only Canon's top of the line speedlites support Flash Exposure Bracketing (FEB). If Canon which speedlite are you using the 550EX, 580EX, 580EX II, 600EX/ 600EX-RT, 600EX II-RT or EL-1.
It doesn't matter the flash what matters is focus bracket shooting is so fast I don't think there is a flash that can fire 50 or more shots in a couple seconds. So having a delay to slow the speed it does to take all shots lets a flash recover between each shot. I am using Canon 430EXII flash. I think there is a camera out there like Panasonic I think it is could be wrong, that has the option to set a delay between shots. It would be easy for Canon to do just add this timer in the menu.
Yes, the 430EXII is under powered for fast flashing but if Canon put in a delay between shots for the focus bracketing this would solve the issue. It would be easy to do just add a adjustable delay setting between shots will allow the flash to recover. If Canon had a place to give suggestions I would submit but can't find such a place.
I was thinking flash exposure bracketing not focus bracketing. The 400EX (430EX series & 470EX-AI) series NEVER supported flash exposure bracketing. Probably because it couldn't keep up with the camera. So the feature was reserved to the 550EX, 580EX, 580EX II, 600EX/ 600EX-RT, 600EX II-RT or EL-1. These speedlites have faster recharging times than the 400EX (430EX & 470EX-AI) series. What other speedlites have you tried on the camera. Every speedlite has a limit to how fast it recharge. Also fps goes down when using a speedlite.
Focus Bracketing has been a feature for quite a while, so I doubt they are gonna add anything like flash delay. It's simplistic at best and I imagine it's going to stay that way. However, you can go HERE and scroll to the very bottom and at the end of the copyright data, you will see a "[+] feedback" link.
Personally, I use battery powered LED panels with diffusers when doing focus stacking. My setup has brightness and color temperature adjustments, and it also has a remote control, which is pretty handy.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
04/20/2023: New firmware version 1.4.1 is available for EOS R3
03/30/2023: New firmware updates are available.
2/07/2023: New product announcements!EOS R8 EOS R50RF-S55-210mm F5-7.1 IS STMRF24-50mm F4.5-6.3 IS STMRF15-30mm F4.5-6.3 IS STM