Mammoth Memory

Convex lens use – Binoculars

Binoculars are two telescopes mounted side by side, one for each eye. Like a telescope, the problem is that, with two lenses for each side, the image is upside down and rotated 180°. In binoculars, they solve this problem not with a third lens, as with the terrestrial telescope, but with prisms.

Without the third lens, the length of the binoculars can be kept shorter. Prisms erect and reverse the image.

One half of a binocular set with a cut away the other side showing the convex lenses and prisms used within

If you followed the path of a ray of light through a telescope and then through binoculars of the same power, the distance the ray would travel would be the same. But in binoculars, the ray extends through the prism. They call this folding the light ray.

Prism and convex lens layout found within one  half of a binocular set

The light is folded. If you measured the length of the ray it would be as long as a telescope of the same power.

Binoculars are made so they do not take up as much room, as a telescope.


NOTE: There are usually a lot more inter-connecting lenses in binoculars to correct the effects of light aberration, a distortion of the spectrum of coloured light which means different colours refract at slightly different angles.



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