From the September 2010 issue

What does “maximum usable” magnification mean?

Jon Owen, Tampa, Florida
By | Published: September 27, 2010 | Last updated on May 18, 2023
Celestron C8-NGT Newtonian reflector and C8-SGT Schmidt Cassegrain
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.