Tony Flanders wrote:

Also worth remembering that most pro scopes these days are F/2
or thereabouts.

But it's also worth noting that they're not for visual use. Also, they
often use only a very small portion of the center of the field -- star
images, for example -- for science. And many have optics after the
primary (far more elaborate and expensive than a Paracorr) that increase
the effective focal length of the telescope by as much as 25x.

Mike Simmons