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Retardation by a fraction of a wavelength, of the rays of light that pass through the object, compared to the rays passing through the surrounding medium, produces the ‘phase’ differences between the two types of rays. In the phase contrast microscope, ‘phase’ differences are converted into differences in intensity of light, producing light & dark contrast in the image.
1. For examining internal details of the cell.
2. For examining live unstained microorganisms in a suspending fluid.