To compute the magnification of an eyepiece divide the telescope focal length by the eyepiece focal length:

Power = Scope Focal Length (mm) / Eyepiece Focal Length (mm)

Examples:
C-8 with an aperture of 203 mm and focal ratio of 10 = 2030 mm
Power with a 20 mm ep = 2030 mm / 20 mm = 101x

8” f/6 newt = 8” * 25.4 mm/inch * 6 = 1220 mm focal length
Power with a 20 mm ep = 1220 mm / 20 mm = 61x

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