Schmidt-Newton telescope

The optical design of the Schmidt-Newton telescope combines elements from both the Schmidt camera and the Newtonian telescope. In this system the parabolic primary mirror common in newtonian reflector is replaced by a spherical mirror, which introduces spherical aberration. This is corrected by the Schmidt corrector plate, like that used in Schmidt-Cassegrain telescopes. From the Newtonian, it inherits the elliptic secondary mirror.

Advantages

Spherical mirrors are much easier to make, especially in short focal ratios. Telescopes using this design should have a short focal ratio of around f/4 making them well suited for astrophotography or CCD imaging. However, this advantage is not relevant for visual use.

Schmidt-Newtonian telescopes suffers from less coma than a Newtonian of the same focal ratio, although it still has some (coma-correcting devices can eliminate them). It also costs less than a Schmidt-Cassegrain telescope as the mirrors can be ground from a single piece of either pyrex or BK-12 optical glass and can use a standard focuser in place of the specialized focuser needed to obtain the correct focus. For example, an 8" Schmidt-Cassegrain costs an average of $1,200 USD while a larger Schmidt-Newtonian costs approximately the same, the latter's larger size allowing the collection of 50% more starlight than the 8-inch SCT. The Schmidt-Newtonian also allows the use of a smaller secondary mirror, unlike a traditional Newtonian of its size, thus reducing the problems of secondary obstruction characterized in short-focus Newtonian and Dobsonian telescopes.

Currently, Meade is the only commercial manufacturer of Schmidt-Newtonian telescopes, offering 6, 8, and 10-inch models on its LXD-75 "GO-TO" equatorial mount.