Binoculars are optical instruments that consist of two small side-mounted telescopes that utilize a series of lenses to provide magnification and three-dimensional viewing of distant objects. Binoculars operate by focusing light between an objective lens, an ocular lens and a prism.
While binoculars operate using the same principles as a telescope, they typically feature shorter body length, a wider field of view and three-dimensional viewing. Through use of a prism, binoculars are able to increase the distance between lenses that light must travel through without requiring an increase in overall body length. Binoculars make use of a larger objective lens that provides initial magnification and a smaller ocular lens that provides focus and clarity.
The most common type of binoculars make use of an offset prism arrangement that was invented by a 19th-century Italian physicist named Ignazio Porro. Unlike Porro-prism binoculars, roof-prism binoculars feature a more compact shape and straight-barreled design made possible through use of a prism that has a more complex shape. Porro-prism binoculars are more suitable for astronomy, while roof-prism models work better for viewing terrestrial objects. Binoculars are typically designed to magnify the image of an object by up to 12 times, although more powerful models able to provide greater magnification do exist.