Unlike the compound light microscope which uses light to image the sample, the electron microscope uses electrons to generate an image of the sample. That's fine, but what does this really mean to us? The SEM has a much greater resolution capability than the light microscope because the wavelength of the electrons is about 100,000 times smaller than the wavelength of light. Resolution is the ability to distinguish between two closely-spaced points.
The best resolution of the light microscope is 0.2 µm or 200 nm. Remember that one micron (µm) also known as a micrometer is 10-6 meters or one thousandth of a millimeter or 1000 nanometers (nm for short).
The resolution of our scanning electron microscope is 3 to 6 nm. That's almost 100 times better than the light microscope. This is why we can see so much more detail with electron microscopes than light microscopes.
Another reason why electron micrographs (pictures taken with an electron microscope) look so detailed is often due to the magnification, in addition to the resolution. The highest useful magnification of an objective lens in the light microscope is 100 times. When you look through the eyepiece this often adds another 10 times magnification. Thus, the highest magnification of the light microscope is 1000 times. The highest magnification of our scanning electron microscope is 300,000 times! That's 300 times more than the light microscope. Although the SEM magnification is very high, you are not able to see individual atoms at this magnification.
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David J. Wright and Shirley J. Wright
Department of Biology, The University of Dayton.
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Copyright © 1999 Shirley J. Wright (Shirley.Wright@notes.udayton.edu)