dark-field illumination


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Related to dark-field illumination: dark ground illumination, oblique illumination, Dark field microscopy

dark-field il·lu·mi·na·tion

a procedure in which a black circular shield is used to block most of the vertically directed rays of light (for example, the field is dark), and a circumferential, suitably angled, mirrored surface is used to direct the peripheral rays horizontally against the object, thereby reflecting the light vertically through the objective lens and along the optic axis; thus, the object is well illuminated in a contrasting dark background.

dark-field illumination

The illumination of an object under a microscope in which the central or axial light rays are stopped and the object is illuminated by light rays coming from the sides, which causes the object to appear light against a dark background. This technique is used to observe extremely small objects such as spirochetes or colloid particles.
See also: illumination