An analogy is drawn in which the optical system in a microscope corresponds to a communication channel; the illumination, to a carrier; and the effect of the object on the illumination, to modulation of the carrier. It is hoped that new techniques in each field can be suggested by their analogs in the other. One such suggestion concerning a new method for obtaining phase contrast microscopy is presented.
In the analogy, axial lighting of an object the transparency of which varies from point to point corresponds to a carrier, amplitude modulated and passed before detection through a channel that extends on both sides of the carrier frequency. Dark field illumination of an object corresponds to passing only one side band of a carrier to the detector. Illumination of a transparent object with varying optical thickness corresponds to phase modulation of a carrier. The phase ring in a phase contrast microscope has an analog in one method of recovering phase modulation, and the optical analog of another method is presented as another way to obtain phase contrast.
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