Definition: Binoculars, also referred to as field glasses, are optical magnification instruments that consist of two telescopes mounted together so that you can view objects that are at a distance. Binoculars enable viewers to use both eyes (binocular vision) to view magnified images of objects that are far away.
Binoculars are described by two numbers, for example 7x35, 8x40, or 10x50. The first number is the magnification (or power) and the second is the diameter of the objective lens (in millimeters). Binoculars used most commonly for bird and wildlife watching are 7x, 8x, or 10x.
There are three basic types of binoculars, based on the type of prism they contain. to If it weren't for the prisms in binoculars, you would see an upside-down, mirror-reflection of the world through your binoculars. Prisms sort out the image so it reaches the eye in proper orientation without such surprises. There are several types of prisms that accomplish this:
- Roof prism - straight profile, eyepieces in line with objective lenses, fairly new design.
- Porro prism - classic design, eyepieces set closer together than the objective lenses.
- Reverse porro prism - eyepieces set wider than the objective lenses, common in compact binoculars.
