Seconding the recommendation above! tbh I'd stick with the Canon Control Ring Mount Adapter EF-EOS R just to be safe... I'm still kinda new to this but I've heard some third-party ones can get wobbly with heavy glass like that 70-200. You might wanna consider the official one to keep that weather sealing intact!! gl!

> I need something rock-solid that won't introduce any communication lag. Sooo honestly, all the official Canon adapters use the exact same electronic pass-through pins. This matters cuz it means AF speed and burst rates are literally identical across all models—there's no communication lag at all! For your situation, I would suggest the basic Canon Mount Adapter EF-EOS R. It's built like a tank, weather-sealed, and handles heavy glass like the Canon EF 70-200mm f/2.8L IS II USM perfectly for way less money. gl!

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Just wanted to say thanks for everyone chiming in. Super helpful discussion.

Huh interesting. I had no idea. The more you know I guess 🤷

@Reply #5 - good point! Most people here are basically saying you gotta stick with the Canon Mount Adapter EF-EOS R or the control ring version if you want it to last. I guess the logic is that the official stuff is the only way to keep that R5 sealing tight and the AF snappy. Honestly though, I tried to go the budget route and it was a massive letdown. I picked up a cheaper Viltrox EF-R2 Mount Adapter thinking I could save some cash for more glass, but the play in the mount was scary with my heavy lenses. I actually tried to DIY a fix by tightening the internal screws and adding a thin shim I cut from a soda can to stop the wobble... it worked for a week then the communication errors started again. Totally not as good as expected and super frustrating during a shoot.

• Stick to the official Canon Control Ring Mount Adapter EF-EOS R if you want that native feel.
• Maybe look at the Canon Drop-In Filter Mount Adapter EF-EOS R with Variable ND Filter if you do video work.
• Avoid the knockoffs for anything heavier than a light prime. I am not 100% sure but I think the drop-in version is just as sturdy as the others. Someone told me it feels a bit different because of the filter slot, but I havent held one myself yet. Just stay away from the cheap stuff if youre shooting pro gigs... definitely not worth the stress imo.

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I totally agree with the others that staying official is the best move here. Since ur shooting with an R5 and those heavier L lenses, the structural integrity of the mount is basically the most important thing to keep in mind. Third-party options can sometimes have a tiny bit of play in the mount that gets worse over time with that heavy 85mm f1.2 glass, and that can lead to weird intermittent connection drops or even light leaks if ur not careful. If that connection breaks for even a split second during a burst, it can really mess up the R5s tracking logic. But before you pull the trigger, I have a couple questions to see what makes the most sense for ur workflow:

• Are you shooting in harsh environments where you need the absolute maximum weather sealing protection?
• Do you plan on getting one adapter for each lens to leave them semi-permanently mounted, or will you be swapping a single adapter back and forth between your glass in the middle of fast-paced shoots? That swapping speed vs seal integrity is a big factor for reliability in the field! Honestly, having that extra peace of mind when ur swinging a 70-200 around is worth every penny.