A monocular is a modified refracting telescope used to magnify the images of distant objects by passing light through a series of lenses and sometimes prisms; the use of prisms results in a lightweight telescope. Volume and weight are less than half those of binoculars of similar optical properties, making it easy to carry. Monoculars produce 2-dimensional images, while binoculars add perception of depth (3 dimensions).
A monocular with a straight optical path is relatively long; prisms can be used to fold the optical path to make an instrument which is much shorter (see the article on binoculars for details).
Monoculars, sometimes called telescopes when used in this capacity, are used wherever a magnified 2-dimensional image of a distant object is required (Though some may be used to look at objects closer).
Visually impaired people may use monoculars to see objects at distances at which people with normal vision do not have difficulty, e.g., to read text on a chalkboard or projection screen. Applications for viewing more distant objects include natural history, hunting, marine and military applications.
When high magnification, a bright image, and good resolution of distant images are required, a relatively large instrument is preferred, often mounted on a tripod. Smaller pocket-sized "pocket scopes" can be used for less stringent applications.