binocular

A binocular, commonly referred to as binoculars, is an optical instrument consisting of two aligned telescopes mounted side by side and controlled by a single focusing mechanism. The purpose is to present a single, magnified image to each eye, enabling stereoscopic vision and improved depth perception when viewing distant objects.

Each side contains an objective lens, a set of prisms, and an eyepiece. Light enters through the objective, is redirected by prisms to correct orientation, and is magnified by the eyepiece. The two tubes are connected by a hinge that allows adjustment of the interpupillary distance to suit the observer. Focusing is typically achieved by a central knob, with a diopter adjustment to compensate for differences between eyes.

Prisms are a distinguishing feature of binoculars. Porro prisms offset the objective and eyepiece to produce a wider field of view and greater depth, while roof prisms align the lenses for a more compact, streamlined body. Coatings reduce light loss; common terms include coated, multi-coated, and fully multi-coated.

Key specifications include magnification (such as 8x), objective diameter (such as 42 mm), and the resulting exit pupil (objective divided by magnification). Other important factors are field of view, close focus, eye relief, brightness, and weight. Variants include compact models, water- or fog-proof designs, and image-stabilized types.

Common uses span birdwatching, hunting, astronomy, marine navigation, and general terrestrial viewing. Proper care involves cleaning with a soft cloth, avoiding abrasive contact, and storing in a protective case to maintain optical performance.