coudé focus

various telescopes and how they focus

A coudé focus is a telescopic focus used primarily for spectroscopy. In this arrangement light from the primary mirror is reflected along the polar axis to focus at a fixed place separate from the moving parts of the telescope, or in an entirely separate room of the observatory (the coudé room), where large pieces of equipment can be fitted without interfering with the telescope's balance. The word comes from a French word meaning "bent like an elbow," not from a person's name.