Binoculars aka field glasses are like two telescopes pointed at the same area. It is easy to perceive depth because it has two lenses and not just one, like a monocular.

The binoculars have been around since about the 17th century after telescopes have been invented. People use to mount two telescopes side by side and looked through them with both eyes.

Between the 1850-1890s, a prism type of binocular was invented that allowed greater depth perception by allowing the eye pieces to be spaced wider apart. These binoculars allow greater magnification.

The most affordable binoculars are porro prisms that allow for brighter images and are precise instruments. These binoculars are wider and sometimes need to be re-aligned.

An expensive kind of prism binocular is the roof prism binocular. This binocular is smaller and narrower but loses some brightness. The good think about them is that they usually never have to be re-alligned. They are also much lighter. Optical coating fixes this problem. That is why many roof prism binoculars are coated.

Optical Coating is a great feature that helps make a brighter image by reducing the amount of light that is reflected. Reflected light inside the binoculars makes the image hazy.

General Binoculars are focused by moving a round wheel that focuses both telescopes at once. More sophisticated binoculars use independent focus which means that each side of the binocular needs to be adjusted individually.

Some binoculars have image stabilization technology which dampen sudden movement. It can usually be turned on or off by the user. This means that very high powered binoculars can be hand held when normally they couldn't. The image quality is not always as good for stabilized binoculars, and they are usually more expensive.

Coin-operated binoculars are very popular in many tourist attractions. They allow a more detailed view. These are always mounted on a pedestal and are usually high powered.

Military Binoculars are usually hand held and at a magnification of 5x or 7x. Military binoculars are more rugged and sturdy than regular binoculars and they also use independent focusing because it is more sturdy than central focusing. Most military binoculars also have special features that help it work when wet or to block out laser beams. Sea binoculars are meant to be easier on the eyes because of the sea rocking back and forth.

Astronomical Binoculars allow people to view certain elements of the sky from far away. There are many moons and planets that can be viewed with binoculars. Pluto, Eris and Uranus can all be seen easier with the use of binoculars. Some users use lower magnification binoculars so they can have a larger field of view than if they used a higher magnification.