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Telescopes from the Ground Up

Spherical aberration in mirrors

The shape of a spherical telescope mirror causes a problem called spherical aberration.

In spherical aberration, parallel light rays that bounce off the central region of a spherical mirror focus farther away than light rays that bounce off the edges. The result is many focal points, which produce a blurry image. To get a clear image, all rays need to focus at the same point.

Diagram demonstrating spherical aberration caused by a spherical concave mirror.
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