Maximum usable magnification is a rough number that gives observers an idea of the upper magnification limit they could expect from a specific telescope. An 8-inch Schmidt-Cassegrain, for example, would have a maximum usable magnification of 400x.
Astronomy: James Forbes
“Maximum usable” magnification is a rough number someone about 30 years ago invented to give observers an idea of the upper magnification limit they could expect from their telescope.
