EOS R + Speedlite @ F1.8

[random.lt]

Hello All,
Could anyone try to replicate my problem with E-TTL??

I'm using bounced flash (580EXII) and if aperture is less than F2.0 (1.8/1.6/1.4) TTL is not metering right and pictures come out VERY dark. Tried with 2 different flash units, tried with all lens faster than F2.0 I'm also using "control" adapter.
So I narrowed it down to:
When the aperture is set to lower than F2.0 then:
- if ISO set to AUTO, then during flash exposure ISO drops dramatically (e.g. from 1600 to 250)
- if ISO set to some value, ISO doesn't drop but exposure is still too dark (flash firing is much weaker)

Basically I cannot get properly exposed shot with flash and aperture lower than F2.0.

- EOS R
- 580 EX II
- Control Ring mount adapter
- Lenses: Sigma 35/1.4 Art / Sigma 50/1.4 / Sigma 85/1.4 << could be miscommunication here?
- Av, Tv, Fv, M modes (basically - doesn't matter)

 

[Viggo]

Just tried in Av with ETTL and f1.2 with the RF and it’s properly exposed. Have you changed exposure compensation for the flash?

I unfortunately have no EF lenses to test with the adapter.

 

[random.lt]

Just tried in Av with ETTL and f1.2 with the RF and it’s properly exposed. Have you changed exposure compensation for the flash?

I unfortunately have no EF lenses to test with the adapter.

No, no FEC applied. Once I change aperture to F2.0 - image is properly exposed.
Don't have RF lenses to test. Maybe I'll go to the camera shop to try that.