Telescopes

There is more than just one type of telescope, and the one you choose will likely depend on the application for which it is best suited.

• Refractors are usually the most expensive per aperture and are best for planetary or binary-star observation because of the sharpness and detail that only a refractor can deliver. Also, because there is no central obstruction (as is the case for Catadioptric and Newtonian scopes), there is greater contrast.



• Newtonians are the cheapest per aperture and are usually best for deep-sky observation because of the greater apertures made possible by less expensive optics (mirrors instead of lenses). There are generally two types of Newtonian telescopes - German Equatorial Mount and Dobsonian (made popular by John Dobson).



• Catadioptrics are more expensive per aperture than Newtonians, but usually less expensive than refractors and are considered to be somewhat general purpose (planetary and deep sky). There are two types of Catadioptrics - Schmidt-Cassegrain and Maksutov. Catadioptric scopes are very popular because of their more compact design. The light that enters is reflected by the primary mirror (a short-focal-length spherical) to the secondary mirror (a convex) which then increases the focal length to the eyepiece. These types of telescopes also use a corrector plate at the front end of the scope to 'correct' for spherical aberration.

Here are four of the most popular telescope suppliers.