With decent stabilization, which is a given for any usable wildlife lanes, you can use a shutter speed that's about half of the one over focal length rule. So for example instead of 1/600th for a 600 mm lens, you can use 1/300th if it's really dim.
A decent rule of thumb is that in broad daylight at f/8, you can shoot 1/100th at ISO 100. So you're only about two stops away from optimal in daylight. And of course, those who can afford the f/4 version of a lens can regain those stops.
I actually kind of liked the somewhat weird experiment Canon recently did, a fixed 800 mm Prime at f/11. I had to return it, not because of the noise but because the autofocus was flaky and it was somewhat inconvenient to not be able to Zoom out.
With decent stabilization, which is a given for any usable wildlife lanes, you can use a shutter speed that's about half of the one over focal length rule. So for example instead of 1/600th for a 600 mm lens, you can use 1/300th if it's really dim.
A decent rule of thumb is that in broad daylight at f/8, you can shoot 1/100th at ISO 100. So you're only about two stops away from optimal in daylight. And of course, those who can afford the f/4 version of a lens can regain those stops.
I actually kind of liked the somewhat weird experiment Canon recently did, a fixed 800 mm Prime at f/11. I had to return it, not because of the noise but because the autofocus was flaky and it was somewhat inconvenient to not be able to Zoom out.