Tom Reichner wrote in post #18784999
For me and for the people that I know and shoot with, the value of f4 and f2.8 supertelephotos has everything to do with how they render the out-of-focus background, and nothing at all to do with shutter speed.
When I state the conditions for a point of normalization, it has nothing to do with what "should" be done. Obviously, any parameter can become unbound, like exposure time, when the camera and subject are relatively stable. Normalizations are meant for demands.
We don't really care about shutter speed except for those instances when we're shooting subjects in motion. Even at 600mm and 800mm with no IS, one can get tack sharp images at 1/100th of a second and slower if they know what they're doing and have good long lens technique.
In many scenarios, those cheaper f5.6 and f6.3 600mm lenses just don't render backgrounds as pleasingly as the $10,000 big whites.
Remember, my post was in response to a discussion about the best lenses in the world, and had nothing to do with what is practical or reasonable or what works for the masses.
I listed some of the benefits of the bigger lenses; I didn't say that you have to take advantage of all of them.
I said that one of the benefits will disappear with better AF systems, which was my main point. When I mentioned "the same shutter speed", it was to say that a bigger lens gives less noise if you do need the (same) shutter speed because of magnification (or subject motion)..
I really struggle hard to figure out why, when I make conditional statements, that people want to challenge what I said as if I said this is what people "should" do, or what "is", when I actually wrote about "if" or "when". It is really getting tiring.