Light microscopes use glass lenses to bend and focus light rays and produce enlarged images of small objects.

The resolution of a light microscope is determined by the numerical aperture of its lens system and by the wavelength of the light it employs. Maximum resolution is about 0.2 micrometers.

Because most microorganisms are colorless and therefore not easily seen in the bright-field microscope, they are usually fixed and stained before observation.

The transmission electron microscope achieves great resolution (about 0.5 nanometer) by using electron beams of very short wavelength rather than visible light.

External features can be observed in great detail with the scanning electron microscope, which generates an image by scanning a fine electron beam over the surface of specimens rather than projecting electrons through them.