Schmidt–Newtonian telescope

A Schmidt–Newtonian telescope or Schmidt–Newton telescope is a catadioptric telescope that combines elements from both the Schmidt camera and the Newtonian telescope. In this telescope design, a spherical primary mirror is combined with a Schmidt corrector plate, which corrects the spherical aberration and holds the secondary mirror.

Source: Wikipedia — Schmidt–Newtonian telescope (CC BY-SA 4.0)