Canon 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.

[Waddizzle]

Is the camera refocusing between shots?

What about recharging times?

[karmlol]

Focus is in one-shot mode, it's not refocusing between shots (also happens on manual focus mode). The flash power is manual and identical between all three bursts, so it should be the same. It can clearly do bursts as fast as the third one, it just doesn't in the first two cases, and the only difference is that it's looking at a darker subject.

I suspect the preview image exposure (which is a larger delta from the underexposed image) is causing this delay, but I don't know why and I don't know how to circumvent it. I like that it brightens the image for the initial focus acquisition, however it shouldn't slow down my flash burst speed beyond that.

[deebatman316]

If the flash can’t keep up with the burst rate of the camera. The camera will slow down automatically for the speedlite.

[karmlol]

You are correct in your statement, however I don't think that is at play in my scenario. If it were the speedlite slowing it down in my example, why then does it have full 20+ fps burst speed in the 3rd burst, but less than 8 in the 1st burst, when both are at the EXACT SAME flash power, shutter speed etcetera?

If you watch the first video I linked, where I showcased my issue, you will see my camera do 3 vastly different burst rates at IDENTICAL (manual) exposure and flash power settings. If the flash couldn't keep up and that were the only issue, then the burst speed would be the same in all 3 bursts.

[deebatman316]

Are you letting it recharge completely (red pilot light) vs partially recharged (green pilot light). If so then the flash hasn't completely recharged yet. Are you using an adapted EF lens are they Canon brand or adapted 3rd Party lenses. Are you using native RF lenses. A lot of older EF lenses are NOT fully compatible with the new high fps mirrorless cameras. A lot of older EF lenses don't support 12 fps. Very old EF lenses with Arc Form Drive AF motors from the beginning of the EOS line only support 3-4 fps. There isn't a way around the limitation because the AF and aperture control take place sequentially instead of at the same time. When the camera is set to Servo AF then known as "AI Servo". I don't know why Canon dropped "AI" from the name. But this AF motor was discontinued in 1992 and replaced by Micro Motor. But some lenses such as the 50mm compact macro remained in production for years before being discontinued in 2018.

[karmlol]

The flash is fully charged before each burst. And as you can see in my video if you watch it, the first burst at the darkest object is the slowest, the second burst at a medium-dark object is faster, but the last burst of the three (right after the first 2) at a bright object is the fastest. All settings, including flash power, are set to manual and the same for each burst.

I am using an EF adapted lens (EF 100mm f/2.8L Macro with RF adapter), but again, when using manual settings and IDENTICAL aperture/shutter speed/flash power, the bursts should all be the same speed - and clearly the camera/lens/adapter/flash combination CAN drive the full 20fps speed burst, I do it right after the first 2 bursts, with the exact same manual settings.

The camera is set to one shot AF or manual focus, and the issue occurs on both of those settings. It's not AF related.

[Waddizzle]

“ The flash is fully charged before each burst. “

I was not asking about battery recharging.  I was referring to the discharge circuit that actually drives the lighting system.

I do not believe my colleagues are, either. 

[deebatman316]

Do you think the lens’ aperture cannot stop down fast enough.

[karmlol]

I didn't mean battery charging, I meant recharged. I'm not taking burst upon burst in hasty succession and blaming fps drops on that. You can see in my video, the fastest burst is the last one. (And there were no major soaking bursts right before the video.) The behavior is also fully consistent when repeated, regardless of the order. The only factor is the brightness of the subject.