RF 400, or EF 400 with adapter?

lokatz wrote:

Still fairly new to the Canon world, so I'm hoping someone can help me with this:

I am contemplating getting a 400mm f/2.8 lens for my R5. From what I can see, it appears to make more sense to get the latest version of the EF lens and put it on the body via a control ring adapter since the RF lens has no control ring. I like the added flexibility the control ring gives me, even if its placement is quite inconvenient.

Availability put aside, is there ANY disadvantage to this that I need to be aware of and that would speak for getting the RF lens instead?

My take, worthy less than the 2 proverbial cents, is simply...

If you are on the market for a new lens, go for the RF version. If you are ok with a used lens, get the EF mkIII version.

I am speculating like everyone else here. My assumption is that the RF version is 100% identical to the EF mkIII version with an adapter bolted on.

Ultimately, I think that, if there were material differences between the 2 version, Canon would have advertised them explicitly. I am sure that the RF version is great, but I also think that it is as great as the EF mkIII version, no more no less.

Based on this assumption, I assume that:

• there is a minor disadvantage with the RF version in that you cannot have a control ring. Personally it wouldn't be a big deal to me, but YMMV
  • I see no issue with not being able to use the adapter with the drop-in filter, since those lenses already have a drop-in filter
• there is a minor advantage with the RF version in that there is 1 less mechanical coupling, therefore the camera+lens combo may be a little more robust
• the AF of the RF version will be indeed faster with a R3/R1, but in the same way the AF of the EF version is faster with a 1D body. It's all about bigger batteries. So I suspect that the EF mkIII version will be equally faster when used with a R3/R1