Optical reference
Celestron X-Cel LX 18mm: focal length, field and the magnification it gives
What the Celestron X-Cel LX 18mm 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 X-Cel LX 18mm gives 36x in a 650 mm scope, 67x in a 1200 mm scope, 113x in a 2032 mm scope, because magnification is the telescope's focal length divided by this eyepiece's 18 mm focal length.
Its 60 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 18 mm focal length divided by the telescope's focal ratio, so at f/5 the exit pupil is 3.6 mm and at f/10 it is 1.8 mm.
The 1.25 in barrel decides which focusers it fits: a 1.25 in barrel fits both dedicated 1.25 in focusers and the 1.25 in adapter of a 2 in focuser.