Telescope Equations

It can be confusing understanding how to work out what you are seeing through a scope, so knowing what magnification and field of view you are getting really helps. Below are some basic equations which will allow you to work this out for yourself:

M      = Magnification
Fs      = Focal length of Scope
A        = Aperture of Scope
Fr       = Focal Ratio of Scope
Fe      = Focal length of Eyepiece
AFoV  = Apparent Field of View of Eyepiece
TFoV  = True Field of View of Eyepiece
FS       = FieldStop of Eyepiece
EP      = Exit Pupil



M = Fs / Fe

TFoV = AFoV / M     

         = Fe x AFoV / Fs

         = 57.3 x FS / Fs

EP = A / M

     = A x Fe / Fs

     = Fe / Fr