dark-field illumination


1. a procedure in which a black circular shield is used to block most of the vertically directed rays of light (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-ground illumination

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