Optical reference
Explore Scientific 30mm 82 Degree: focal length, field and the magnification it gives
What the Explore Scientific 30mm 82 Degree 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 Explore Scientific 30mm 82 Degree gives 22x in a 650 mm scope, 40x in a 1200 mm scope, 68x in a 2032 mm scope, because magnification is the telescope's focal length divided by this eyepiece's 30 mm focal length.
Its 82 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 30 mm focal length divided by the telescope's focal ratio, so at f/5 the exit pupil is 6 mm and at f/10 it is 3 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.