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Basics of Microscopes

What is a phase contrast microscope?

With a conventional biological microscope, it is difficult to observe colorless, transparent cells while they are alive. A phase contrast microscope makes it possible by utilizing two characteristics of light, diffraction and interference, to visualize specimens based on brightness differences (contrast).

Principle With regard to periodic movements, such as sinusoidal waves, the phase represents the portion of the wave that has elapsed relative to the origin. Light is also an oscillation and the phase changes, when passing through an object, between the light that has passed through (diffracted light) and the remaining light (direct light). Even if the object is colorless and transparent, there is still a change in phase when light pass through it. This phase contrast is converted into brightness differences to observe specimens.
Features - Transparent cells can be observed without staining them because the phase contrast can be converted into brightness differences.
- because it is not necessary to stain cells, cell division and other processes can be observed in a living state.
Structure Because diffracted light is too weak to be normally observed by the eye, a phase plate is located at the focal point of light between the objective lens and the image surface so that only the phase of the direct light changes. This generates contrast on the image surface.
Structural features include a ring aperture, instead of a pinhole, on the focal plane of the converging lens and a phase plate on the rear focal plane of the objective lens.

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