yo, mirrorless cameras have a shorter distance to the sensor, which is why we need these! It’s AMAZING cuz your EF glass actually focus BETTER now. Honestly, skip the Viltrox EF-EOS R Mount Adapter for those heavy lenses. I recommend the Canon Mount Adapter EF-EOS R for total reliability. The Canon Control Ring Mount Adapter EF-EOS R is cool but pricey... do u actually need the dial?? TL;DR: Stick with official Canon adapters!

Seconding the recommendation above. In my experience, the Meike MK-EFTR-A Auto Focus Mount Adapter is a safer budget pick that wont ruin your expensive glass... worth a shot?

Just saw this thread and had to jump in because i was terrified of my 70-200mm snapping a cheap adapter. I tried a no-name brand first and the wobble was unreal... honestly so scary! I finally went with the Metabones Canon EF Lens to RF-mount T Smart Adapter and the build quality is just amazing. It feels like one solid piece of metal and the weather sealing is fantastic! Couple quick tips for the heavy glass:

• Always support the lens, not just the body, when you are carrying it.
• Clean those pins regularly with a dry cloth so the communication stays snappy. Seriously, dont go too cheap when youre using heavy L series glass. Its just not worth the stress!

I've spent a lot of time measuring the tolerances on these mounts because even a fraction of a millimeter of play can mess with the plane of focus on that 85mm f/1.2L. Over the years, I've tried many, and honestly, the internal flocking on the Viltrox EF-R2 Mount Adapter is surprisingly good at preventing internal reflections compared to the cheaper no-name brands. The electrical pins on the Commlite CM-EF-EOS R Mount Adapter are gold-plated and I havent seen any data dropouts even with the heavy 70-200mm pulling on the mount. If you're coming from a 5D IV, you're used to tank-like build quality. While the Canon ones are the only ones with true weather-resistant gaskets at the flange, the Viltrox R2 gives you that control ring functionality for way less money without sacrificing the signal integrity. TL;DR: Grab the Viltrox EF-R2 Mount Adapter if you want the control ring for cheap, but stick with the official Canon Mount Adapter EF-EOS R if you need that rubber gasket for shooting in the elements.

yo, been thinking about your move from the 5D IV... honestly I made that same jump a year ago and its basically a whole new world for AF accuracy. I remember being super worried about my older glass cuz those 85mm motors are like, ancient and slow. In my current setup, I actually went with the version that has the drop-in filter slot since I do a lot of landscape stuff and it REALLY simplifies things. Technically, the pins align perfectly so the signal speed is the same, but the weather sealing on the more expensive ones is definitely worth it if you shoot in the rain like I do. Check out these resources for the technical specs:
* The Digital Picture (they've got GREAT AF speed comparison charts)
* Canon Professional Network (look for their white papers on EF to RF communication)
* Firmware update databases to see if your 85mm needs a patch for the R6 IBIS Anyway, just make sure you check for firmware updates for those older lenses! gl!