Optical microscopes, through their use of visible wavelengths of light, are the simplest and hence most widely used type of microscope. Recent research has shown that even simple microscopes, those with a single small lens, gave amazingly clear images to the earliest microscopists. Today compound microscopes, i.e., especially those with a series of lenses, serve uses in many fields of science, particularly biology and geology. Optical microscopes use refractive lenses, typically of glass and occasionally of plastic, to focus light into the eye or another light detector. Typical magnification of a light microscope is up to 1500x with a theoretical resolution of around 0.2 micrometres. Specialised techniques like the scanning confocal microscopy may exceed this magnification but the resolution is an insurmountable diffraction limit. Other microscopes which use electromagnetic wavelengths not visible to the human eye are often called optical microscopes. The most common of these, due to its high resolution yet no requirement for a vacuum like electron microscopes, is the x-ray microscope.Optical Configurations. There are two basic configurations of optical microscope in use, the simple with only one lens and compound with many lenses.

Simple optical microscope-
A simple microscope is a microscope that uses only one lens for magnification, and is the original light microscope. Van Leeuwenhoek’s microscopes consisted of a single, small, convex lens mounted on a plate with a mechanism to hold the material to be examined, the sample or specimen. Demonstrations by British microscopist Brian J. Ford have produced surprisingly detailed images from such basic instruments. The use of a single, convex lens to magnify objects for viewing is found today only in the magnifying glass, the hand-lens, and the loupe.

Compound optical microscope-
The compound microscope uses a set of many lenses in order to maximize magnification. The diagram below shows a compound microscope. In its simplest form as used by Robert Hooke, for example - the compound microscope would have a single glass lens of short focal length for the objective, and another single glass lens for the eyepiece or ocular lens. Modern microscopes of this kind are usually more complex, with multiple lens components in both objective and eyepiece assemblies. These multi-component lenses are designed to reduce aberrations, particularly chromatic aberration and spherical aberration. In modern microscopes the mirror is replaced by a lamp unit providing stable, controllable illumination.

Stereo Microscope-
The stereo or dissecting microscope is designed differently from the diagrams above, and serves a different purpose. It uses two separate optical paths with two objectives and two eyepieces to provide slightly different viewing angles to the left and right eyes. In this way it produces a three-dimensional or 3D visualization of the sample being examined. The stereo microscope is often used to study the surfaces of solid specimens or to carry out close work such as sorting, dissection, microsurgery, watch-making, small circuit board manufacture or inspection, and the like. Great working distance and depth of field here are important qualities for this type of microscope. Both qualities are inversely correlated with resolution: the higher the resolution like the shorter the distance at which two adjacent points can be distinguished as separate, the smaller the depth of field and working distance. A stereo microscope has a useful magnification up to 100×. The resolution is maximally in the order of an average 10× objective in a compound microscope, and often much lower. The stereo microscope should not be confused with a compound microscope equipped with binocular eyepieces. In such a microscope both eyes see the same image, but the binocular eyepieces provide greater viewing comfort. However, the image in such a microscope is no different from that obtained with a single monocular eyepiece.