Simple Light Microscope

A simple microscope is one of the simplest of all-optical instruments. It consists of a single convex lens of a short focal length. The object to be seen by the simple microscope is kept just inside the focus of the lens. When viewed from the other side, a virtual, erect, and enlarged image of the object is seen.

Magnifying power (M) of the simple microscope is given by

M = 1 + D / f

Where D is the least distance of distinct vision (it is equal to 25 cm for a normal human eye) and f is the focal length of the convex lens.

When the eye is fully relaxed, the magnification of the simple microscope is given by

M = D / f

A simple microscope is used as a magnifier for watch repairers, specimen observers, palmists, etc. A simple microscope cannot be used to observe tiny objects like viruses and bacteria.