600mm f/11 or 800mm f/11 - which one would you buy?

Messier Object wrote:

Neither would entice me to buy an RF mount camera

Message to Canon:
Sorry Canon, if you want me to buy into the EOS R system, cheap long slow lenses won't do the trick. You need to offer me an APS-C EOS R7 as an upgrade to my 7D2, or you need to offer a very high Megapixel R camera which will have a seamless in-built 1.6x crop mode to 32Mpix and with fps and AF performance better than the 7D2

Peter

"Neither" was my first instinct too, but that's possibly just because I'm used to thinking that superteles need to be f/4 for use in low light. Set that preconception aside and think afresh and maybe there is a usage case for both of these.

You need that kind of wide aperture speed when you are shooting at have low light levels and are limited in your ISO by when noise becomes a problem. When I first started with digital, anything above ISO800 was problematic, and I managed just fine with f/4 super teles most of the time - actually I had too, because it's as good as it got.

Yesterday evening, I was out in my garden getting perfectly usable shots of bats (pipistrelles) in flight at ISO 25600 f/5.6 with a 1DX MkIII at well after 22:00. That's *six* full stops over the f/4 ISO800 combo, whereas f/4 to f/11 is just three. f/11 also gives you a lot more usable DoF, especially at 600mm or 800mm where it can be a challenge to get larger animals sharp front-to-back if you're not stopped down to f/8 or f/11 anyway.

So, if Canon can pair these with a sensor with the ISO performance of a 1DX III, provide acceptable AF performance at f/11, *and* give decent image quality for the money, then I can well believe that a lot of wildlife, and especially bird photographers, that can accept the loss of background seperation will be all over these. From what I've seen of the rumoured specs though, neither the R5 or R6 is going to be that body, and there's still not even a really plausible hint of an R1.

Andy