580 EX II (flash exposure compensation doesn't work off-camera)

[SLF]

I'm using this on my canon R6 II with a Youngnuo YN622C II flash trigger (622 setting) on my camera and off-camera flash. Both triggers are on the same group and channel, and the full flash works off-camera. Whereas I can adjust the FEC with flash on-camera, I can't control it with flash off-camera. The flash is set to slave; if set as master , the scene is underexposed and the flash doesn't cover the entire scene. Perhaps some other setting is incompatible?

[SignifDigits]

What are you External Speedlite Control settings in Menu -> Shooting Menu Tab 1 (red) -> [External Speedlite control]?

Are you saying that you cannot control the FEC manually on the flash itself when you say "I can't control it with flash off-camera" or where are you expecting to control the FEC, exactly?

[Waddizzle]

You need to contact Youngnuo.  If the Canon flash works on the camera, then there’s nothing wrong with it.

It just doesn’t work with the third party trigger. You have a third party trigger problem.

[SignifDigits]

Or you can contact the seller if you bought from B&H or someone like them.  They could also assist you.

[Waddizzle]

“ Or you can contact the seller if you bought from B&H or someone like them.  They could also assist you. “

Even better!

[SLF]

I can set the FEC off-camera flash on the flash's screen, but it doesn't change the flash exposure. I think Waddizzle might be right that the problem is related to the flash trigger. If so, might operating the flash in manual mode work?

[SLF]

If so, what would be a compatible trigger?

[SignifDigits]

I have heard Canon's new firmware fixed their 2.4GHz interference issues, so for best compatibility consider Canon's line at https://www.usa.canon.com/shop/digital-cameras/camera-accessories/speedlite-transmitters.   They are more expensive, but you don't have to pay for separate receiver triggers.  Most, if not all, of the negative reviews are prior to the release of the new firmware last fall, and at least one site user said it fixed their problems - https://community.usa.canon.com/t5/Speedlite-Flashes/Updated-EL-5-and-ST-E10-Firmware-to-Version-1-2... .  I don't have any personal experience with them personally.

I have the Godox XR receivers and the Godox X3 C camera transmitter, but haven't used them on a shoot yet, so I don't have a ton of experience using them other than my living room testing where they seems to function just fine.  I chose to not use the X3 Pro due to some reviews mentioning a loose mounting and I prefer the smaller size of the X3 anyway.  I bought them from B&H.

So, those would be the options that I would recommend for research.

[SLF]

Given my efforts and replies to my query, I've concluded that the cheapest fix (though clunky) is to run the flash in manual mode where I can adjust flash exposure while off-camera.

[SignifDigits]

Sounds like a plan!  Best wishes.