Aphase-contrast microscope is a type of microscope used for examining
transparent specimens. It is widely used in biology for studying cells and
thin slices of tissue. Light passing through the specimen slows down and
becomes out of phase with the original light.
Differences in thickness or density in the specimen cause diffraction
patterns. A phase-contrast plate converts these to interference
patterns, which manifest themselves as large contrasts in brightness
of different parts of microscope image.