A form of microscopy commonly used for examining objects too small to be seen by bright field microscopy. For low or medium power work, the underside of the condenser is fitted with an opaque disc which only allows peripheral rays to pass through the condenser, thus forming a hollow cone of light whose apex is focused in the plane of the specimen. This specimen scatters the rays, some of which enter the objective and form a bright image of the specimen against a dark background (hence, dark-field). For high power work a special oil immersion is used.