A while back I rented the EF-EOS R 0.71x adapter for my C70 and used my existing EF 50mm f/1.2 lens. Absolutely loved the low-light capability (f/0.9!), but there were costs:
I haven't rented the RF 35mm f/1.8 IS lens, but will do so soon. Other than the four-times less light-gathering, it has IS and I'd have the full AF area to work with.
With the focal reducer setup in very dark scenes I plan to capture, I could be at either ISO 400 or 800. With the RF 35mm, I'd need to be at ISO 1600 or 3200 so less clean for sure.
Finally, the usage would be very much run-and-gun, so that's why I'm a bit concerned about the reduced AF area.
What option would you choose? Perhaps there are pros/cons I'm not thinking of that can help tip the scales on my decision. Thanks.
Edit: Forgot to add that I mostly use an RF 24-70mm f/2.8 IS with the C70. The above two lens options would be specific to low-light work.
I have the RF 35mm f/1.8 STM, and the RF (not EF) 50mm f/1.2.
They're both great, but to my mind, the 35 is a "low-end" lens -- at only (!) £500 -- whereas the 50mm is a "serious" high-end lens.
The 50mm is HEAVY -- really heavy. You really know you have a massive hunk of glass in your hand with that thing. The 35 is super-light by comparison (305g), which is nice for portability, but again makes it feel like more of a budget lens.
The 50 focusses fast and silent, as you would expect from a USM lens. The 35 is SLOW and noisy -- again as you would expect for STM.
One thing is that the 35 has a pretty decent macro; I can fill the frame on the C70 with a subject about 50mm wide.
Of course with the 50mm EF, plus the adapter, you will have a pretty large package. The 35 is super-compact by comparison.
I haven't compared image quality. I guess there are sites that have charts etc.
One thing to bear in mind is that with field reducing adapters, the aperture does NOT necesssarily multiply, because there will be a limit on the aperture you can get; so I wouldn't be sure that you're really getting f/0.9, unless you've verified that. Nicolas at Media Division has a fantastic video on fast lenses, if you haven't seen it, which explains this, as well as great videos on many other technical subjects:
If you haven't seen this, really check it out. He'll show you how to get f/0.7.
The Media Division channel:
Thank you, Ian. This helps quite a bit. I have a stereo mic mounted on the C70. I don't use the handle, so it's directly on the hot shoe and thus closer to the lens. When I rent the RF 35mm, will see just how much lens noise is picked up. The slow-focus will probably be a deal-killer, though I will compare to the EF 50mm with focal reducer setup.
Yes, not looking forward to the RF 50mm f/1.2 due to the size and weight (eventually I'll move my photo camera to mirrorless and the 50mm will be the first lens I get for that).
For the f/0.9 statement I made, that was only in reference to the light-gathering ability. Sorry, I should have made that more clear.
Media Division is awesome; I've seen those videos that you linked a while back.