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Institute of Biochemistry and Biophysics (IBB),
University of Tehran, Tehran, Islamic Republic of Iran.
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When one think of an electron microscope and is uses, light magnification is usually thought to be the prime objective. The final magnification id a compound Light microscope is merely the product of the objective lens and eyepiece powers. So why can we not just use more powerful light microscopes to produce infinitely light magnification? In other words, why do we need electron microscope if simple light microscopes can produce any power of magnification required? The answer -resolving power- brings us to a very important concept in any type of microscopy.



The resolving power of a microscope can be define simply as the ability of the microscope to discriminate between two separate objects. It can be shown that the resolving power of a microscope is limited by the wavelength of light used, and in general, in order to resolved, objects must be greater than one-half the wavelength of light. That is why we use electron for illumination in electron microscope. A functioning TEM requires a source of electrons (called an electron gun), an illumination system, image forming lenses, magnifying lenses, a mean to view and record the final image, and a means to maintain the electron path (or column) under a vacuum.