Optical reference
Celestron Omni 56mm Plossl: focal length, field and the magnification it gives
What the Celestron Omni 56mm Plossl measures and the magnification and true field it produces once you drop it into a telescope of a given focal length.
Published specifications
An eyepiece has no magnification of its own. The Celestron Omni 56mm Plossl gives 12x in a 650 mm scope, 21x in a 1200 mm scope, 36x in a 2032 mm scope, because magnification is the telescope's focal length divided by this eyepiece's 56 mm focal length.
Its 47 degree apparent field becomes the true field of view once divided by that magnification: wider in a short-focal-length scope, narrower in a long one. The exit pupil equals this 56 mm focal length divided by the telescope's focal ratio, so at f/5 the exit pupil is 11.2 mm and at f/10 it is 5.6 mm.
The 2 in barrel decides which focusers it fits: a 2 in barrel needs a 2 in focuser or diagonal and will not drop into a 1.25 in one.