Phase Contrast Microscope optical train - أطلس مختبرات العرب

The most important concept underlying the design of a phase contrast microscope is the segregation of surround and diffracted wavefronts emerging from the specimen, which are projected onto different locations in the objective rear focal plane (the diffraction plane at the objective rear aperture). In addition, the amplitude of the surround (undeviated) light must be reduced and the phase advanced or retarded (by a quarter wavelength) in order to maximize differences in intensity between the specimen and background in the image plane. The mechanism for generating relative phase retardation is a two-step process, with the diffracted waves being retarded in phase by a quarter wavelength at the specimen, while the surround waves are advanced (or retarded) in phase by a phase plate positioned in or very near the objective rear focal plane. Only two specialized accessories are required to convert a brightfield microscope for phase contrast observation. A specially designed annular diaphragm, which is matched in diameter and optically conjugate to an internal phase plate residing in the objective rear focal plane, is placed in the condenser front focal plane.