Most early binoculars used Galilean optics that is, they used a convex objective and a concave eyepiece lens. Some are equipped for night vision.Īlmost from the invention of the telescope in the 17th century the advantages of mounting two of them side by side for binocular vision seems to have been explored.

Modern military binoculars have filters that block laser weapons used against them.

Late-20th century technology made this application redundant ( radar laser sights guided missiles &c).

Warships used very large binocular naval rangefinders (up to 15 metres separation of the two objective lenses, weight 10 tons) for ranging gun targets 25 km away in World War II.

Metallic mirror coating for its prisms.

Reducing reflection via anti-reflective coatings also reduces the amount of 'lost' light bouncing around inside the binocular which can making the image appear hazy (low contrast). Anti-reflective coatings reduce light lost at every optical surface through reflection at each surface.

Anti-reflective: not just relections off the front lens, but every lens and prism.

This scale allows the distance to the object to be estimated if the object height is known. Many binoculars have range finding reticle (scale) superimposed on the view. Eye relief can be particularly important for eyeglass wearers. Binoculars may have eye relief ranging from a few millimeters to 2.5 centimeters (1 inch) or more. The longer the focal length of the eyepiece, the greater the eye relief.

It is the distance the observer must position his or her eye behind the eyepiece in order to see the image. Eye relief: Eye relief is the distance from the rear eyepiece lens to the exit pupil or eye point.

Large binoculars have independent focussing for each 'telescope' (each side).These features are present in some or all binoculars: Night vision binoculars use photocathode electronics to intensify the image.īinoculars are also used for theatre (opera glasses), birdwatching and amateur astronomy.Īnti-reflective coatings on large naval binoculars. Binoculars are also standard issue in all armies. Heavy ones can be mounted on swivels to scan the horizon. The Royal Navy used single telescopes, but now all ships have heavy binoculars. They allow a telescope user to use both eyes. That is why a binocular is shorter than standard telescopes of similar power.īinoculars were invented in the 17th century. They have prisms inside, which bend the light so to shorten the length of the tubes. This way, when someone looks through the binoculars at a far-away object, it looks much closer. The two telescopes have lenses that focus light and magnify the image, a process called magnification. They are made of a pair of matched telescopes that are held in front of the user's eyes. The lenses magnify the imageīinoculars are a kind of tool that lets people see far-away things more clearly, using a technology called optics.

Inside binoculars are prisms which fold the light and make the instrument shorter than a standard telescope.

Binocular power explained