A microscope is an optical instrument that is used for viewing very minute objects which can not be seen distinctly by the naked eye. Simple microscope or magnifying glass comprising of a single converging lens was known in ancient times. But the first compound microscope is thought to have been invented by a Dutch spectacle-maker, Zacharias Janssen, around 1590. Compound microscopes incorporating “achromatic” lenses became available around 1840s.
In simple words it is an instrument for producing enlarged images of smaller objects. In modern times we can see magnified images of bacteria, cells of living beings and many other minute objects with it and study their structures. Do you know how enlarged images of minute objects are produced by a microscope?
A microscope consists of two convex lenses of short focal length fitted at the two ends of a hollow pipe. The lens towards the object is called the objective lens and has a very small focal length. The other lens positioned towards the eye is called the eye lens or eye-piece and has a larger focal length. The object under observation is placed on the platform of the microscope near the objective lens which makes an enlarged real image. This very image acts as an object for the eye lens which makes an enlarged virtual image. Again this image acts as an object for the eye and its image is formed on the retina of the eye. In this way small objects look bigger and their minute structures become clearer. Microscope can magnify the image of an object even up to 1000 times its actual size. Since these instruments use light for illuminating the object, they are called optical microscopes.
In Electron Microscope, beams of electron are used rather than light to study objects too small for conventional microscopes. It is also used for structural defects and composition studies in a wide range of biological and inorganic materials.
The various lenses of the electron microscope allow the operator to see details of an object magnified almost upto a million times. However, many specimens may deteriorate under the electron beams at these limits.
