^Near point case
It the object is placed between F & P of a convex lens such that the images at near point (25 cm) is formed as shown,
then the magnifying power of lens is
Magnifying power of a simple microscope can be increased by decreasing the focal length of the lens, however generally it is not preferred, as then spherical & chromatic both defects becomes more pronounced. Also it is difficult to grind lenses of very short focal lengths. Consequently a simple microscope has a limited maximum magnification (≤ 9) for realistic focal lengths. For much larger magnifications, one uses two lenses, one compounding the effect of the other.