\(m=\left(\frac{L}{f_{o}}\right)\left(\frac{D}{f_{e}}\right)\)

where \(f_{o}\) and \(f_{e}\) are the focal lengths of the objective and eyepiece respéctively and \(L\) is the distance between their focal points and \(D\) is the least distance of distinct vision.

If \(f_{o}\) increases, then \(m\) will decrease. 

Magnifying power of a telescope, \(m=\frac{f_{o}}{f_{e}}\)

where \(f_{o}\) and \(f_{e}\) are the focal lengths of the objective and eyepiece respectively.

If \(f_0\), increases, then \(m\) will increase,