Apparently DoF only affects distant midground, leaving background intact. While this was probably done to avoid mistakes of blurry clouds or moons, using anything more than "Simple" doesn't look realistic at all.
Take a look at this example, using "Circular" setting.

Notice that Midground looks so much more blurred than mountains in the Background. This shouldn't be possible.

Not only is not realistic, but looks quite ugly and smudged, IMO of course.
And this is what "Simple" looks like:

Far more natural and on par with the background.
I'm not sure if they could "mark" certain faraway objects in the sky, like moons, clouds etc. to be as they are, while having Backgrounds on the ground blurred as much as the Midground, to avoid the situation that currently is with Circular and Smooth setting.
Edited by maboleth on July 19, 2021 9:48AM