This may not be all that bad as an answer to those who are still wanting to stay with EF Mounts.

Wide Angle Adapter Test With Black Magic Cinema Camera. - YouTube

Chris, I love it; well done! Wait, what’s this...distortion right there in the sweet spot...oh no, pardon me; it’s just your belly, I think!

Seriously, as you say looks like not a bad quick and not too dirty approach. I look forward to your comments as you experiment more with that adapter.

Cheers.

Here are a couple of more tests with the adapter, including one on a 24mm vintage Nikon.

Wide Angle Adapter Test 2 - YouTube

Nikon 24mm with wide adapter - YouTube

This video demonstrates adapter on a slider. Edge to edge seems pretty clean to my eyes.


Slider with Wide Adapter Test with Black Magic Cinema Camera EF - YouTube