Biology in the Laboratory

Seeing Small

What distinguishes the different types of microscopes?

Microscopes have played a central role in the development of cell biology, allowing scientists to observe cells and cell structures that are not visible to the human eye. The two basic types of microscopes are light microscopes and electron microscopes, the major differences being the source of illumination and the construction of the lenses. Light microscopes utilize visible light as the source of illumination and a series of glass lenses; electron microscopes utilize a beam of electrons emitted by a heated tungsten filament as the source of illumination, and the lens system consists of a series of electromagnets.

Advances using optical techniques also led to the development of specialized light microscopes, including fluorescence microscopy, phase-contrast microscopy, and differential interference-contrast microscopy. In fluorescence microscopy, a fluorescent dye is introduced to specific molecules. Both phase-contrast microscopy and differential interference-contrast microscopy use techniques that enhance and amplify slight changes in the phase of transmitted light as it passes through a structure that has a different refractive index than the surrounding medium.


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