[Klaus]

I'm a little puzzled by those MTFs, to be honest.

These are almost as good as for the old 200mm f/2.8L. I have a hard time believing that a f/11 lens is as good as an f/2.8 lens. But let's see ...

[Brightcolours]

You mean diffraction wise? Are the Canon MTF's adjusted for diffraction effects?

[Klaus]

https://www.youtube.com/watch?v=EZ9y5YCHnn8

[faint]

I'm a little puzzled by those MTFs, to be honest.

These are almost as good as for the old 200mm f/2.8L. I have a hard time believing that a f/11 lens is as good as an f/2.8 lens. But let's see ...

MTF are usually provided wide open. The only exception I can think of, is Zeiss - they provide additional MTFs at F4 or F5.6. If I remember correctly, their MTFs are also measured, not theoretical (I would not mind more Zeiss reviews : )

In addition, focal length is 3x or 4x in mm, so MTF should be higher, if following the rule of thumb.

[Klaus]

We are talking about f/11 - thus diffraction-limited lenses. As hinted by Brightcolors - if Canon ignores diffraction, they make sense. Otherwise I have my doubts.
Diffraction is limiting these lenses to about 16-20 megapixels after all - and that's just the theoretical peak.

[Arthur Macmillan]

Off the top of my head, I'd say these lenses are brilliant! They lack versatility but give a huge telephoto length that is actually affordable. Centering should not be a big problem. Nor will aperture movement vibration. BTW, probably it has been discussed, but the new EF 600mm f/4L IS USM Mk-iii is rumored to have IS problems that are the result of the of the redesigned aperture. At $13,000 I would be pretty upset. At the price of the new RF 600mm F/11 STM, I think I could put up with what I expect to be really good performance.

As for DLA, this is a theoretical limit, and yet it doesn't seem to effect all lenses equally. I'm totally guessing, but with a very narrow field of view on a distant object the light rays are going to hit the front element which are very nearly parallel. The front two bonded defractive elements should bring them to the other elements after which they are even more parallel. We'll see, but I'm guessing the results will be such that many birders will have to have one. If nothing else, to be used as a spotting scope!

I haven't seen actual photos yet. BC's links did not work for me.

Lastly, I must have it wrong, but I thought Canon's MTF charts were done at F/8 (where possible?). I could be wrong. DLA was not a thing before high MP sensors, so maybe this has changed, if it ever was the case. But one would want a standard that could be applied to (almost) every lens!

This is exciting stuff!

[Brightcolours]

Canon's MTFs are done wide open. They are calculated, not measured, and do not take diffraction softening into account.

[Klaus]

This statement is a bit fuzzy here - it's f/11 only. Anyway ... the proof is in the pudding.

[Arthur Macmillan]

This is probably a little off the wall, but take a look again at the diagram for the 800mm f/11: https://cweb.canon.jp/eos/rf/lineup/rf800-f11/image/spec/spec-lens-construction.png

Couldn't Canon take the same exact lens, and extend it less by the difference in the focal flange distance between the EF-s mount and the RF mount and make the same lens available for the Canon 7D Mk-ii/ 70D/ 80D / 90D? Hopefully they could use an EF/s mount because the imager circle for the APS-C is a lot smaller than for the FF sensor. Then use it in live view for shots with and angle of view of 800mm x 1.6 or 1280mm? Yes, I know it isn't going to happen but imagine all that reach! If it could AF in live view that would interesting to try.

Would the 7D Mkii would be able to focus and track? I don't see why we DSLR guys should miss out on everything!

[Klaus]

Most DSLRs can AF up to f/5.6. The pro models can do f/8. But f/11 is nothing that a manufacturer would certify for a DSLR.