Optical reference
Tele Vue 15mm Plossl: focal length, field and the magnification it gives
What the Tele Vue 15mm 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 Tele Vue 15mm Plossl gives 43x in a 650 mm scope, 80x in a 1200 mm scope, 135x in a 2032 mm scope, because magnification is the telescope's focal length divided by this eyepiece's 15 mm focal length.
Its 50 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 15 mm focal length divided by the telescope's focal ratio, so at f/5 the exit pupil is 3 mm and at f/10 it is 1.5 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.