I do find it very surprising that neither Canon nor Nikon nor Sony offer a 300 2.8 in their current mirrorless lineup, nor do any of them have one on their roadmap (as far as I know). Considering what a common pro lens this was for SLR, it seems like a glaring omission. Adding a built-in 1.4x extender seems to me like it would give it wide appeal.
It’s actually not significantly ‘slower’ in a relevant way. Yes, the f/number is larger, but the focal length is correspondingly longer so the physical aperture is the same ~71mm. That means at the same shutter speed the number of photons reaching the sensor is the same, and same number of photons means same noise. OTOH, if you crop your 400mm shot to a 500mm FoV, you’ll have less total light and thus a noisier image.
In the context of what @neuroanatomist responded to: the RF100-500 has the same maximum physical aperture as the EF100-400II, so where the focal lengths overlap, from 100mm to 400mm, the same amount of photons will hit the sensor, regardless of the lens. The angle difference you're talking about only comes into play when using the 'bonus' 400-500mm range.
Agreed that between 100-400mm the two are basically identical.
If you are photographing a duck with a 400/5.6 and a 500/7.1, then the same number of photons hit the image of the duck in both cases.
The RF 100-500mm is stopped down to f/6.3 at 400mm and so the effective diameter drops from ~71mm to ~63mm. Accordingly, the EF 100-400mm lets in more light at 400mm than does the RF 100-500mm at 400mm.
I wrote photographing a duck, not part of a duck. But, that's not the point: the point is the photon flux per unit area of object in the image depends on the area of the front element (etrance pupil) and not the f-number of the lene.
And my point is that it (photon flux per unit area of the object plane reaching the sensor plane) also depends on the distance to the object. "Zooming with feet", when possible, gives better results.
Zooming with your feet when moving forwards with a prime lens might give better results than zooming in. But, having to move backwards with a prime lens to fit in a duck rather than zoom out and be closer is the opposite. The “zooming with your feet is better“ comment we see so often verges on the silly as it often can’t be done.
It’s a depth of field issue with sports, editors (and myself) want those backgrounds to drop as much as possible. I own a 100-400, had a 100-500 to use for a week from Canon, it was fine. There are few sports that I shoot that the range is ideal, but I do struggle with backgrounds being too in focus.
Correct, looking through the little hole in the plexiglass at NHL, more light passing through and less background in focus is the goal. I also use a 400 2.8 and almost always shot at 2.8
Interesting. If your framing at 500mm is not too tight, 500mm f/7.1 gives a shallower DoF than 400mm f/5.6 for a subject at the same distance. Having said that, from 363-471mm the RF 100-500 is at f/6.3, in that overlapping range of 363-400mm you lose 1/3-stop of subject isolation. At the other end, the 100-500 stays f/4.5 a little longer. Anywhere in the zoom range, I suspect you'd be hard-pressed to see a 1/3-stop difference have any meaningful impact on a final image, especially if you were not comparing controlled images side-by-side.
