Hobbies And Interests
Schmidt-Cassegrain Telescope
The Schmidt-Cassegrain is the most popular telescope-type among serious amateur astronomers, because it provides an excellent balance between competing factors: aperture and image quality, portability and ease of use, and cost. The "Schmidt-Cass" is distinguished by an aspheric, or Schmidt, corrector plate mounted in the front of the optical tube. A corrector plate serves two purposes: it corrects the image aberrations inherent in the spherical primary, and provides a central mounting surface for the secondary mirror, which reflects converging light rays back through a central hole in the primary. This permits the eyepiece to be placed at the rear of the tube, a convenient position for observing.
Schmidt-Newtonian Telescope
The Schmidt-Newtonian combines elements of the Schmidt design and the Newtonian telescope. The "Schmidt-Newt," like the Newtonian, has its focuser positioned near the front of the optical tube, perpendicular to the optical axis. The Schmidt-Newtonian is a compact telescope similar to the Schmidt-Cass: the focal plane of the primary is at the back of the aspheric corrector plate, resulting in an optical tube that is shorter, per unit of aperture, than those of most Newtonian-reflecting or refracting telescopes. The Schmidt-Newt offers a wide field of view, but is less popular than the similarly priced Schmidt-Cass, because the location of the focuser/eyepiece often makes it difficult to use.
Maksutov-Cassegrain Telescope
The Maksutov-Cassegrain is similar in appearance to the Schmidt-Cassegrain. The difference is in the corrector plate, which is a deeply curved spherical meniscus. The relatively small secondary mirror is, again, fixed to the back of the corrector plate to produce a "folded" optical path. Like the Schmidt-Cass, the Maksutov-Cassegrain is a compact scope of long focal length. The "Mak," however, outperforms the Schmidt-Cass in image quality, because it combines a more sophisticated optical system with a smaller secondary mirror obstruction. The optics produce a wide and flat field of view, and images of exceptional quality, but at a higher price.
Maksutov-Newtonian Telescope
The Maksutov-Newtonian has a meniscus-type corrector plate, which, like those of the other catadioptric scopes, reduces the image aberrations and troublesome air currents characteristic of the open-tube Newtonian reflector. The "Mak-Newt" offers a wider, flatter field of view than a comparable Mak-Cass or Newtonian, and the smaller central obstruction, typically about 20 percent of aperture, contributes to its superb imagery. The short focal ratios of these scopes yield magnificent wide-field views. But the Maksutov optics make them expensive.
Small Newtonian Reflectors
Spherical mirrors are relatively easy to manufacture. For this reason, they are often used in small, inexpensive Newtonians. These beginner scopes have relatively long tubes and apertures between 3 and 4.5 inches. The long focal ratios of these scopes reduce optical aberrations to tolerable levels.