CassegrainSystem

A Cassegrain system is a type of reflecting telescope that uses a parabolic primary mirror and a hyperbolic secondary mirror. The light from a distant object first strikes the primary mirror, which is concave and reflects the light back towards a focal point. Before reaching this focal point, the light encounters the secondary mirror, which is convex and hyperbolic in shape. This secondary mirror reflects the light back through a hole in the center of the primary mirror, where it is then focused by an eyepiece or a detector.

This design offers several advantages. The primary mirror's parabolic shape is ideal for collecting parallel rays of light from celestial objects. The hyperbolic secondary mirror effectively folds the light path, allowing for a longer focal length in a more compact telescope tube. This reduction in tube length is a significant practical benefit, making the telescope easier to build, mount, and maneuver.

The Cassegrain design is widely used in both amateur and professional astronomy. Variations exist, such as the Gregorian telescope, which uses a concave elliptical secondary mirror, and the Ritchey-Chrétien telescope, which uses two hyperbolic mirrors. The Ritchey-Chrétien design, in particular, is favored for large astronomical observatories because it corrects for coma, an optical aberration that can distort images, especially at the edges. The fundamental principle of using a primary mirror to collect light and a secondary mirror to redirect it remains central to all Cassegrain-type telescopes.