coudé focus

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A focal point in an equatorially mounted telescope that lies along the polar axis (see diagram). In a Cassegrain telescope, a single flat mirror in the centre of the tube reflects the converging light beam down the polar axis. Other variants, for refractors, involve two large flat mirrors of similar size to the objective, one to direct light along the polar axis and the other to view the chosen part of the sky. Coudé is French for ‘elbow’, referring to the bending of the light path through 90°. The coudé focus is stationary, so large or heavy equipment can be stationed there, often in a separate coudé room. It is often used for spectroscopy.

coudé focus

Subjects: Astronomy and Astrophysics.

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