We know, least distancefor distinct vision in simple microscope is \(D =25\,cm\).
Again we know, when the final image in a simple microscope is formed at
infinity, the object must be situated at the focus \(f\).
\(\therefore\) When the image is at infinity, magnifying power of the microscope is
\(m =\frac{ D }{ f }=\frac{25}{ f }\)