What is the RF mount Greg? I have this lens with the Canon EOS mount but am not aware of an RF option. I see that the Bintel site lists a ‘Canon M’ option which I’m guessing is for the mirror less range of DLSRs.
As for the performance of my ‘EOS’ version, I am very pleased with it. I use it primarily for wide field Nightscape work with my Canon 60Da. I do step the lens down to 5.6 to address improve the coma around the edge of the field and at that setting I am happy with the results that I get.
Here are a couple of links to recent images taken with this lens:
https://astrob.in/y94kxm/B/
https://astrob.in/kngqdt/0/
CS,
Rodney