| 释义 |
dark-field illumination
dark-field illumination n (General Physics) illumination of the field of a microscope from the side so that the specimen is viewed against a dark background dark-field illumination
dark-field illumination[′därk ‚fēld ə‚lüm·ə′nā·shən] (optics) A method of microscope illumination in which the illuminating beam is a hollow cone of light formed by an opaque stop at the center of the condenser large enough to prevent direct light from entering the objective; the specimen is placed at the concentration of the light cone, and is seen with light scattered or diffracted by it. dark-field illumination
dark-field il·lu·mi·na·tiona 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. Synonym(s): dark-ground illuminationdark-field illuminationThe 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: illuminationThesaurusSeeillumination |