What is the maximum magnification power a telescope or spotting scope can achieve?
As described above, the higher the magnification level, the dimmer an image becomes. There is thus a golden rule for the maximum usable magnification (Mmax) of any scope: Mmax=2 x D (mm) Where: D is objective lens diameter measured in mm. For example, for the Nipon 26-78×78 compact zoom scope, its objective lens is 78mm, so the maximum usable magnification power of this scope is 2×78=156 times.
