= Dark-field microscopy
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<Dark-field microscopy> excludes directly transmitted illumination from the <microscope objective>, while admitting <light> scattered by the specimen. A transparent particle can then appear bright against a dark background even when it has little <optical absorption>.
One implementation illuminates the specimen with a hollow cone whose direct rays pass outside the objective's acceptance cone. <Scattering of light> at particles or edges redirects some of this illumination into the objective. Dust and scratches also become bright, so a clean blank specimen is a useful control.<Darkfield Illumination by Nikon Instruments Inc.>[Illumination geometry and discussion of light scattered into the objective]{ref}
Detection is not the same as <optical resolution>: a very small particle may be visible as an unresolved spot whose width is set by the <point spread function>.
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