Canon R5 -using EF lenses?

I'm just switching to Canon; received my R5 yesterday so I have no personal experience with either the EF or RF versions of the 70-200 f2.8. But I have been intensely researching new lenses. Here are 2 reviews from what I consider reliable sources who both say optically the new RF model is about the same as the last EF version- both very good. They say the RF version does have advantages over the EF (weight, length) disadvantages (cost) but image quality is about the same.

https://www.youtube.com/watch?v=_cWsGjdqUnI

https://www.youtube.com/watch?v=wGYQQ2wI1JQ

There are a number of threads on this subject; just search for something like "ef lens on rf camera".

I've got a number of EF lenses and all work better on my R5's than they did on any of my DSLRs, including the 5D Mark 4 and 5Ds R. In all cases, AF is noticeably faster and seems more accurate. For your upcoming event, rather than worry about using the EF lens (be sure to use a Canon EF-RF adapter; doesn't matter which one), study up on the AF modes. You'll likely want to configure Back Button Focus (I use dual BBF; some people I know use 3 buttons).

Your lenses should be fine. I bought the RF 24-105L only so I'd have a native normal zoom range lens for the R5. I also have the EF 24-105L for my DSLRs. I find them about the same. The RF is a little sharper at one end; the EF's sharper at the other. I prefer the EF's ring layout.

As previously mentioned, Canon hasn't (yet?) come out with updated versions of either the 180L or MP-E65 macros, both of which are pretty old designs, yet both work just fine on the R5. The 180L's the only EF I have that I'd consider replacing. I'm not doing massive EF lens replacements. So far I have 3 RF lenses, all of which do more than the EFs I had. 100-500 is more useful for me than 100-400; the 14-35 is more useful for me than the EF 16-35 (better zoom range, much lighter, more compact, but needs more work in post to compensate for optical shortcomings).

Since you already own the lenses you're thinking of using, just use them! I'm sure you'll be satisfied with the results. If you decide to replace any of them, I'd suggest considering the f/4 versions unless you really need f/2.8 for DoF reasons. In DSLRs, faster lenses had the added benefit of providing a brighter viewfinder view, but that advantage is gone with the R5. Also, the R5's high ISO performance means I don't need to open up as much, and I typically want greater DoF anyway, so rarely shoot at faster than f/5.6.

Really, though, the best advice is to use what you have and then decide if it works for you...unless you're particularly eager to part with a lot of money.

Thanks for the good advice below -and to the others who have replied.

A local pal pointed out that having 2 cameras at a race event is critical. So bringing my 7DII for the longer lens shots, and using the R5 with the 15-35RF would probably be the best approach.

I am addicted to low light/golden hour shooting. And prefer faster lenses when possible.

Abbott Schindler wrote:

There are a number of threads on this subject; just search for something like "ef lens on rf camera".

I've got a number of EF lenses and all work better on my R5's than they did on any of my DSLRs, including the 5D Mark 4 and 5Ds R. In all cases, AF is noticeably faster and seems more accurate. For your upcoming event, rather than worry about using the EF lens (be sure to use a Canon EF-RF adapter; doesn't matter which one), study up on the AF modes. You'll likely want to configure Back Button Focus (I use dual BBF; some people I know use 3 buttons).

Your lenses should be fine. I bought the RF 24-105L only so I'd have a native normal zoom range lens for the R5. I also have the EF 24-105L for my DSLRs. I find them about the same. The RF is a little sharper at one end; the EF's sharper at the other. I prefer the EF's ring layout.

As previously mentioned, Canon hasn't (yet?) come out with updated versions of either the 180L or MP-E65 macros, both of which are pretty old designs, yet both work just fine on the R5. The 180L's the only EF I have that I'd consider replacing. I'm not doing massive EF lens replacements. So far I have 3 RF lenses, all of which do more than the EFs I had. 100-500 is more useful for me than 100-400; the 14-35 is more useful for me than the EF 16-35 (better zoom range, much lighter, more compact, but needs more work in post to compensate for optical shortcomings).

Since you already own the lenses you're thinking of using, just use them! I'm sure you'll be satisfied with the results. If you decide to replace any of them, I'd suggest considering the f/4 versions unless you really need f/2.8 for DoF reasons. In DSLRs, faster lenses had the added benefit of providing a brighter viewfinder view, but that advantage is gone with the R5. Also, the R5's high ISO performance means I don't need to open up as much, and I typically want greater DoF anyway, so rarely shoot at faster than f/5.6.

Really, though, the best advice is to use what you have and then decide if it works for you...unless you're particularly eager to part with a lot of money.