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Microbiology

What is dark field or phase microscopy?

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August 06, 2008 6:34PM

The dark-field microscope allow a viewer to observe living, unstained cells and organisms by simply the way in the specimen in which they are illuminated. A hollow cone of light is focused on the specimen in such a way that unreflected and unrefracted rays do not enter the objective. Only light that has been reflected or refracted by the specimen forms an image. The field surrounding the specimen appears black, while the object itself is brightly illuminated. The dark field microscope reveal considerable internal structure in larger eucaryotic microorganisms. A phase-contrast microscope is used when an investigator wants to view living cells in order to observe a dynamic process such as movement or phagocytosis. A phase contrast microscope converts slight difference in refractive index and cell density into easily detected variations in light intensity and is an excellent way to pbserve living cells.