Why do binoculars need prisms?

Prisms are crucial for a good pair of binoculars. We find out why

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The prisms found in binoculars are vital for good views of the night sky. Image Credit: Celestron

The prisms found in binoculars are vital for good views of the night sky. Image Credit: Celestron

Asked by Josh Burns

The prisms in a set of binoculars are vital for image correction and keeping the binoculars small enough to be hand-held. When light passes through the objective lens of a pair of binoculars, the image is inverted. For some viewing applications this wouldn’t be an issue but for many this is a problem. In order to rectify this, complex lens arrangements can be used to correct it. These can often make the instrument longer and trickier to handle. In binoculars prisms are used to make the correction. The prisms also serve to reduce the size of the binoculars. This is a result of their path bending qualities, as the light’s path curls through the prisms, the length of the instrument is reduced making it easier to handle.

Answered by Josh Barker from the National Space Centre

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