R6 uneven vertical banding?!

[mixist]

Below is a photo shooting a white balance card before a portrait shoot yesterday. Canon R6, 135L (1/1600th, F/2, ISO 800, Electronic 1st Curtain shutter mode) using an Aputure 300x for key light. I edited the photo to emphasize an odd problem: notice the uneven vertical banding (wider at the top, narrower at the bottom—never seen anything like it). It would be easy to say that it's the Aputure 300x at fault, but I replicated the EXACT conditions today and there is no more banding. What on EARTH is going on here? Anyone else seen this before?

EDIT: Problem was the shutter mode. I was, indeed, using Electronic 1st Curtain shutter mode. I tested all of them today and Mechanical was clean. Thank you to those who pointed this out!

Canon R6 uneven vertical banding

[Peter · Accepted solution]

Use mechanical shutter.

[Waddizzle]

I agree.  Use the mechanical shutter for this type of shooting scenario.

[mixist]

You are correct! I changed to Mechanical shutter AFTER the shoot and then tried to reproduce the problem, which I couldn’t. What, if any, downsides are there to always keeping the R6 in Mechanical shutter mode? Louder? Wear and tear?

Thank you!

[AtticusLake]

Bear in mind that LED lights dim by flashing on and off very fast.  If your camera happens to be scanning the scene while the light is turning on or off, then illumination will be uneven.

Normally it's not an issue with modern LED fixtures, because their flash time is very fast; but you're using a very fast shutter.  So that could be an issue.

[mixist]

Aputure LightStorm fixtures are high-quality LED lights and supposed to be flicker free up to fairly high shutter speeds (higher than I was using). More testing today…