Schmidt–Cassegrain telescope

A catadioptric telescope that combines a spherical primary mirror with a Schmidt correcting plate and a secondary mirror. The folded optical path gives it a long focal length in a compact tube.

Schmidt corrector plate: A thin aspheric optical plate that corrects spherical aberration in a Schmidt telescope. Its shaped surface corrects the spherical primary mirror’s aberration before light reaches the focus.
Catadioptric system: An optical system that uses both reflective and refractive elements to form images. This is the broader design family combining the telescope’s mirrors and correcting plate.
Newtonian telescope: A reflecting telescope that uses a concave primary mirror and a small diagonal secondary to direct light to a side-mounted focus. Its open tube and side focus contrast with the sealed, rear-focusing folded design.
Amateur astronomy: The observation and study of celestial objects by people outside professional astronomy. Its compact storage and versatility make the design common among amateur observers.
Spherical aberration: An optical aberration in which rays entering a spherical lens or mirror at different distances from the axis focus at different points. The spherical primary mirror would blur images without the correcting plate.
Reflecting telescope: A telescope that uses mirrors as its primary image-forming optical elements. Its spherical primary mirror makes the design fundamentally a reflector with added correction.
Maksutov telescope: A catadioptric telescope that uses a spherical primary mirror and a strongly curved meniscus corrector. It also corrects a compact folded optical path, but uses a different corrector shape.
Astrophotography: The practice of recording astronomical objects using cameras and optical instruments. The long focal length suits small targets, though tracking accuracy becomes demanding.
Secondary mirror: A mirror that redirects light within a reflecting optical system, often toward a focal point behind the primary mirror. It folds the optical path back through the central opening in the primary mirror.
Refraction: The change in a wave’s direction and speed as it passes between materials with different refractive indices. The corrector plate refracts incoming light to compensate for the mirror’s aberration.

Linked from 4 pages

Dobsonian telescopeCompared with: Its compact tube is easier to transport than a comparably capable large Dobsonian, but typically costs more.