Binoculars or field glasses are two telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal mounted military models.
Monoculars are ideally suited to those with vision in only one eye, or where compactness and low weight are important (e.g. hiking). Monoculars are also sometimes preferred where difficulties occur using both eyes through binoculars because of significant eye variation or poor vision in one eye.