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]

I just did the brief experiment. With no flash attached and AF set to manual, I set my R1 up with shutter speed 1/2000, f/5.6 and ISO 6400. I aimed at my lamp and held down the shutter speed for exactly 1 second (or as close as I could). It captured just over 40 separate RAW images. (Also repeated it with autofocus enabled, same results.)

I reduced aperture to f/8 and tried again. It captured about 30 images. So the R1 with RF adapter and EF 100mm f/2.8L Macro lens combination definitely IS capable of capturing 30-40 frames per second at apertures f/5.6 and f/8.

You may be correct that there is a limiting impact of shooting at very small apertures, but that limit is still at most 30fps at f/8, so that cannot explain the drop to ~6 FPS that happened in my video (which was shot at f/5.6 by the way, not f/8, as you can see in the settings I show at the start).

It also cannot explain why that limit wouldn't be the same in the 3 cases I showed in my video.

[deebatman316]

Some EF lenses can support up to 20 FPS in ELECTRONIC shutter mode but NOT mechanical. The EF 100mm F/2.8L Macro IS USM will depending on certain shooting conditions per Canon. But its NOT guaranteed that it can provide exactly 20 FPS. But the EF 100mm F/2.8L Macro IS USM is a lens that likely will support 20 FPS in electronic shutter mode. So it may likely cause the camera to slow down or maintain speed. The 12 FPS limit is for the mechanical shutter mode.

Per Canon 

When the Shutter Mode is set to [Electronic]During continuous shooting, if the following conditions are satisfied, high-speed continuous shooting (maximum burst of 20 shots per sec.) is performed.

The lens is set to maximum aperture except for when using an EF-S lens*.

For details on the lenses, see "List of lenses that the continuous shooting speed of max. approx. 20 fps less likely to decrease".

The continuous shooting speed may change in response to the shutter speed, aperture, aperture status during continuous shooting, subject conditions, brightness (shooting in a dark environment, etc.), type of lens, etc.

List of lenses that the continuous shooting speed of max. approx. 20 fps less likely to decrease This is the list of lenses that the continuous shooting speed of max. approx. 20 fps is less likely to decrease.

[karmlol]

I just showed per practical example that my EF lens hits 40-30 FPS at apertures f/5.6-f/8.

But this is entirely irrelevant. Have you looked at my video? Could you explain *WHY* FPS is lower (around 6FPS) when shooting a darker subject, but MUCH higher when shooting a brighter subject, while exposure, aperture and flash power are manual and IDENTICAL between those three different bursts?

[deebatman316]

Canon did NOT give an exact fps for that lens but it said likely to achieve 20 fps. Flash will slow down your camera. The manual says low lighting conditions could impact burst shooting rates. "The continuous shooting speed may change in response to the shutter speed, aperture, aperture status during continuous shooting, subject conditions, brightness (shooting in a dark environment, etc.), type of lens, etc". Also is the flash getting hot because it will reduce fps automatically if it starts getting hot. Can the flash's capacitors recharge fast enough are you using good batteries. I've had weak batteries cause slow recharge performance.

[deebatman316]

I noticed that you were using rear curtain sync. Rear Curtain sync only works with shutter speeds below 1/30th of sec. 1st Curtain sync is automatically applied if the shutter speed is above 1/30th of sec regardless if or if not set to rear curtain sync.

[karmlol]

Interesting, I didn't know that curtain sync bit. Good to know.

The actual cause of the FPS differences in my example are still a mystery though. Even if the manual says those factors can affect it, I understand that only for the cases where aperture, shutter speed and flash power are NOT locked and dialed in manually. For my case, I do not understand why (outside of my hypothesis involving the disabling of exposure simulation).

[deebatman316]

It doesn't matter if you lock your settings in manually. If the flash is getting hot the camera will slow down. If the flash cannot keep up with the camera it will also slow down.

[karmlol]

Again, you are correct in your statements, however the flash getting hot is not the issue in my case, as you can see in my video. Its behavior is somehow *ONLY* depending on the brightness of the object I photograph, not on the amount of time I wait before bursts, not on the order in which I do the bursts, etcetera.

[deebatman316]

The flash needs more power the brighter it is resulting in longer recharge times. Then the speedlite could overheat faster.

[p4pictures]

Only three cameras can shoot with flash and electronic shutter mode, EOS R3, EOS R5 Mark II and EOS R1, all other EOS R-series cameras will not fire the flash in electronic shutter mode. They will in first curtain electronic and mechanical shutter mode. So only those three models are suitable to test. My EOS R6 Mark II will shoot at 40fps in electronic shutter, but is limited to 12fps with first curtain electronic or mechanical.