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Microscopy

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Phase Contrast Microscopy
Phase Contrast Microscopy, first described in 1934 by Dutch physicist Frits Zernike, is a contrast-enhancing optical technique that can be utilized to produce high-contrast images of transparent specimens, such as living cells (usually in culture), microorganisms, thin tissue slices, lithographic patterns, fibers, latex dispersions, glass fragments, and subcellular particles
(including nuclei and other organelles).
In effect, the phase contrast technique employs an optical mechanism to translate minute variations in phase into corresponding changes in amplitude, which can be visualized as differences in image contrast. One of the major advantages of phase contrast microscopy is that living cells can be examined in their natural state without previously being killed, fixed, and stained. As a result, the dynamics of ongoing biological processes can be observed and recorded in high contrast with sharp clarity of minute specimen detail.

The phase-plate increases the phase difference to half a wavelength.
Destructive interference between the two sorts of light when the image is projected results in the specimen appearing as a dark object.

The phase contrast microscope uses the fact that the light passing through a transparent part of the specimen travels slower and, due to this is shifted compared to the uninfluenced light. This difference in phase is not visible to the human eye. However, the change in phase can be increased to half a wavelength by a transparent phase-plate in the microscope and thereby

2

causing a difference in brightness. This makes the transparent object shine out in contrast to its surroundings. A simple image illustrating the operation mechanism of a Phase Contrast Microscope

The operation of any microscope in the phase contrast mode requires that you first set up proper brightfield illumination, with a centred field

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