Optics 101

Binoculars - How Binoculars Work?

Binoculars can be considered as having two telescopes which are exactly the same placed next to each other and accurately pointing at the same direction. Binoculars allow the user to use both eyes when looking at distant objects.

How Binoculars Work?

Two objective lenses are situated at each end of the binoculars. The purpose of the objective lens is to collect light from the object that the user is looking at and bringing the collected light into focus in the eyepiece lens, which creates a visible and magnified image.

The image generated is backwards and upside down. Corrective elements known as prisms are used to fix this problem and they are situated between the objective lens and the eyepiece lens. The prisms used in binoculars are basically blocks of glass that acts like mirrors. The prisms use internal reflections to bring the beam of light from the objective lens closer together and to correct the orientation of the image created by the objective lens. Two types of prisms are used in binoculars: roof prisms and porro prisms.

Roof prisms allow the manufacture of small and light binoculars. The principle behind roof prism binoculars is that the beam of light is divided into two and brought together again. This process results in a phenomenon known as phase shifting. A decrease in contrast is also observed in roof prism binoculars since less light is sent from the objective lens to the eyepiece lens.

On the other hand, porro prism binoculars use an offset arrangement to line up the objective lens with the eyepiece lens. Porro prism binoculars offer a wider view of view than compared to roof prism binoculars.

Magnification Powers of Binoculars

The magnification of all binoculars is expressed by a pair of numbers, for example 6x40. These sets of numbers represent the light-gathering power of the binoculars. The first number indicates the magnification power of the binoculars, while the second number represents the diameter of the objective lens in millimeters.

Source: AZoOptics

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