what is the magnification of the eyepiece
Eyepieces have focal lengths, too â 25- or 10-mm, for example. To calculate the magnification, simply divide the focal length of the scope by that of the eyepiece. A 2000-mm focal length scope used with a 25-mm eyepiece will therefore deliver 2000/25 = 80 power (or 80x).
For example, consider a 10 mm-focal-length eyepiece of 50Â° apparent field in combination with a scope of 1,000 mm focal length. The magnification will be 100x (that is, 1,000/10) and the true field will be 50Â°/100x, or 0.5Â° â so the full Moon would just nestle within the field of view.