EOS R1: flash burst speed lower when non-flash exposure is underexposed

[karmlol]

Firstly, let me describe my issue: I have an R1 and a 600EX II RT flash. When I set everything to manual (shutter speed, aperture, ISO and flash power), it should take photos at the same burst speed regardless of what I'm shooting (some photos would just end up exposed differently). However I'm finding that when my subject would (without flash) be underexposed, the burst speed WITH flash is much lower, despite everything being identically set on manual.

Here's a video example: https://www.youtube.com/watch?v=cH8uXa50IGA

It starts out black (because of exposure simulation, the scene is underexposed without a flash), but as soon as I half-press the shutter, the scene brightens up. The burst that then follows is slower the darker the subject is, even though shutter speed and flash power are identical.

My suspicion is that it has to do with the scene preview exposure behaviour, where it automatically turns off exposure simulation whenever a flash is attached (or whenever metering starts with a flash attached): https://www.youtube.com/watch?v=ZjWVEQbdi40

I suspect it tries to properly expose the scene because there is a flash attached, increasing aperture to f/2.8 (up from f/5.6) and increasing ISO, and then has to swap back to f/5.6 and ISO 200 again for the photo. (And then back and forth again and again in between burst frames??) I cannot think of any other explanation why the burst rate is different with all those settings identical in full manual mode. Burst rate isn't bottlenecked when not using flash, so that rules out processing or card write speed issues.

Has anyone else come across this issue, and is there any possible workaround that does NOT involve taping off contacts and removing the possibility of using E-TTL?

I've read this thread on a related topic, however my use case is different because my flash burst rates are actually significantly reduced because of this issue, whenever relying on flash to fill an underexposed scene.

[karmlol]

Yes. However in my three bursts, flash power was IDENTICAL because it was locked in MANUALLY at 1/64th power. I really feel like the things I have said many times now are being ignored or not understood. I've clarified this many times now.

[karmlol]

That may have been true before the Canon R1 came out. The R1 is their new flagship camera, and I can confirm (and you can see in the video I linked) that the flash DOES fire in electronic shutter mode. It even has a flash sync speed of up to 1/400th of a second in electronic shutter, full frame mode.

[deebatman316]

The EL-5 is the only speedlite that can keep up with the R3. The 600EX II-RT cannot keep with it in electronic shutter mode. I would think the same would apply for the R1. My old 550EX cannot keep up on my 5D Mark IV. But the 600EX II-RT can because it was released with the 1DX Mark II. Which shoots more fps than the 5D Mark IV. 

[karmlol]

I'm not expecting it to keep up. Very surely the 600EX would not keep up with 40fps. I know that, and that is not my issue.

My issue is, why does it happily do 20fps when shooting a bright subject, but only 6fps when shooting a dark, underexposed subject, AT IDENTICAL, MANUAL EXPOSURE AND FLASH POWER settings.

[deebatman316]

Ambient lighting affects the camera’s metering system. Then you have the buffer too and the flash needing to recharge. 

[karmlol]

As an update, I have not found a fix for this behavior (though still suspect the viewfinder preview to be related to the cause); burst rates are still greatly reduced when shooting dark subjects with flash enabled, even if all settings are dialed in manually and autofocus is on manual or single shot mode.

My 'workaround' has been the in-camera "focus stacking" feature. Using this, I need to pre-define the amount of shots to take (for example, 60 shots), and then press the shutter once to start off a burst. This burst will happen at maximum possible burst rate, so limited only by the flash (and it is obviously MUCH faster than 6fps, even when shooting dark subjects).

The only downside to using this workaround is that I have to pre-determine the amount of shots to take, and that I cannot configure a slightly lower burst rate for a more consistent burst without flash slowdowns halfway in (due to overheating or flash cycle times). In focus stacking mode, it will always fire at max burst rate regardless of my burst settings.

However, I've been able to get some nice stacks this way without being restricted to 6fps. These are two of my first ever (handheld) focus stacking images taken yesterday; I'm quite pleased. Stacking was done using Zerene Stacker.

[NatalyaP]

Greetings karmlol,

I am sorry to hear that your camera and flash are having a performance issue during certain shooting environments. Sometimes things can be more efficiently resolved by discussing the issue in real time with a live agent. Given the nature of this particular issue, I would recommend calling our tech support department by phone. Technical support can be reached at 1-800-652-2666 between Monday and Friday from 9:00 am to 6:00 pm EST.

[karmlol]

I have contacted my local Canon support. The product specialist was able to reproduce the issue in their own environment and it has been escalated to a higher level in Canon Europe. I hope it will eventually find its way to the developers and a firmware update.

[p4pictures]

Thanks for the update. 

[karmlol]

Final update (for now): Canon got back to me and said it's a hardware limitation, but didn't fully explain why.

The workarounds they offered were to either use the mechanical or second curtain electronic shutter, where they say the issue doesn't occur. I will give those a try at a later point.

I did request a change to fix this issue for electronic shutter mode if autofocus mode is set to either single shot or manual. In those cases I feel the re-exposure in between shots should not be needed and could be skipped in favor of the faster burst rate.

I was cautioned that these requests end up with the developers with several international layers in between, and that there's no guarantee they will be fixed and end up in a firmware update, or in what way (paid upgrade or not). But one can hope.