What is 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. The resulting system has less coma and diffraction effects than a Newtonian telescope with a parabolic mirror and a "spider" secondary mirror support. The design uses a 45° flat secondary mirror to view the image, as in a standard Newtonian telescope.