I am sorry FLand aperture used are not beside the point.
Having a 500mm f/4 you had the luxury of 1000mm f/8 or f/10 so closing by 2/3 of a stop at your case. Would you have the sam e luxury with f/7.1 which would make it f/14 and f/16 if you close by 2/3 of a stop?
ISO would become 2000.
7.1 would up to the DLA limit of a future R at 45Mpixels so f/10 is OK I guess but f/16?
I am sure it would make a wonderful portable lens of course. This portability would make it successful depending of course on IQ and fast focusing capability.
Let's wait until it is out.
You're missing my point so I will reiterate as clearly as I know how.
So on all these threads about -f7.1 zoom a number of people have said it's unusable. That is,
f/7.1 is an unusable aperture (in the case of this patent and the recently-announced -500mm f/7.1 zoom)
for long lens work, birds in forests, etc.
These have been blanket statements about aperture, without regard to focal length.
I don't have a photograph to hand taken at 500mm f/7.1 - I could take one with the bare 500L. But I don't need to do that to make my point (which I have repeated on a number of threads), which is that
I have done a tonne of bird photography at f/10 and it's been fine - not too dark most of the time, and the backgrounds are adequately blurred.
Obviously using a zoom with a maximum aperture at the long end of f/7.1 is not precisely the same as using a 500mm + 2x TC stopped down a little. Obviously I have more reach*. But that is not the point being made here.
One last time: f/7.1 is perfectly usable for bird photography (and many other types), sometimes even in low light.
DLA is irrelevant to this discussion, but since you brought it up, the photograph I posted above was taken on a 5Ds, which has even smaller pixels than the rumoured R5. Unless you are cropping more heavily on a higher res sensor, diffraction is no more apparent regardless of resolution.
*as an aside, a shorter FL can produce equally- or even more blurred backgrounds if the MFD is shorter, and I'd expect these zoom lenses to focus closer than the supertelephoto primes.