Medical Definition of Phase-amplitude contrast

1. The separation and recombination of direct vs. Diffracted rays in a light microscope adjusted to Kohler illumination. at the lower focal plane of the condenser there is an annular diaphragm with an opaque central stop. Through this diaphragm rays are focused as a hollow cone onto the specimen. In the back focal plane of the objective there is a conjugate annular diaphragm (phase plate). If here the undiffracted rays are retarded (by a transparent film of proper thickness on the annulus of the phase plate), bright contrast results. If, instead, the phase-delay film is on the central spot, dark contrast results. With either a bright or a dark-contrast phase plate, the annulus is usually coated with a partially absorbing (very thin) film of silver (Zernike method) or carbon soot (Wilska method) to reduce the higher amplitude (intensity) of the undiffracted rays. (05 Aug 1998)

Lexicographical Neighbors of Phase-amplitude Contrast

pharyngotome
pharyngotomes
pharyngotomies
pharyngotomy
pharyngotonsillitis
pharyngotympanic
pharyngotympanic groove
pharyngotympanic tube
pharynx
pharynxes
phascogale
phascogales
phascolome
phascolomes
phase
phase-amplitude contrast (current term)
phase-contrast microscope
phase-locked loop
phase-shift keying
phase I
phase II
phase III
phase III clinical trial
phase II block
phase II clinical trial
phase IV
phase IV clinical trials
phase I block
phase I clinical trial
phase angle

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