Magnifying Glass

Magnifying glass, an optical instrument ordinarily used for studying objects at weak magnifications and with a wide field of view. A magnifying glass consists either of a single simple or achromatic biconvex, plano-convex lens or of a single combination of optical lenses; accordingly, one distinguishes simple, achromatic, and aplanatic magnifying glasses. The magnifying glass finds wide application in natural sciences and medicine as an instrument for studying structures inaccessible to the naked eye but at the same time not sufficiently thin for microscopic research, as well as in medicine for examining skin changes, changes in the eye, etc. A funnel with a biconvex lens inserted into its wide end is called a Brunings magnifying glass. Usually, a magnifying glass is used to obtain an enlarged virtual direct image, but in some cases, for example when examining the fundus of the eye, it is also used to obtain an enlarged real image. The magnifying glass is used either as a hand instrument in a frame with a handle or is mounted on a stand when it is necessary to work with both hands for a long time, as for example during the fine teasing of histological preparations or during the study of small animals. To magnifying glasses is often included the so-called monobinocular dissecting microscope, but the latter consists of two systems—ocular and objective—and therefore such magnifying glasses should more correctly be classified as microscopes.