help

Guest · Posted: Tue Jul 26, 2005 2:25 pm Post subject: help

wat's the diference between a refractor telescope and a cassegrain telescope

opticsplanet.com · Posted: Wed Jul 27, 2005 12:17 pm Post subject:

Hi

A refractor telescope uses lenses (not mirrors) at the top of the telescope to focus light rays into an eyepiece at the bottom of the telescope. It is the same design used in binoculars and most spotting scopes.

A refractor is virtually maintenance free and also the most rugged telescope design. In the most expensive versions, a refractor will produce the brightest and sharpest image per inch of telescope. However, the refractor is also the most expensive telescopes per inch of telescope size; beyond three inches, the refractor goes up very quickly in price. Because of its potential for excellent imaging, the refractor is a popular design for planetary work and in a large enough size, also a good choice for some deep-sky work. However, because of the price and physical size, most amateur refractors do not exceed 6"

A Cassegrain is actually describing two types of scopes commonly used today, the Maksutov-Cassegrain and the Schmidt-Cassegrain. Both are identical except for the corrector plate (lens) used. In these scopes, a combination of lenses and mirrors is used and the optical path is folded. This allows for a very long optical path to be squeezed into a very short tube.

Both types offer many of the advantages of the refractor - good image quality - with the larger size of the reflector. The Maksutov-Cassegrain, commonly known as a "Mak" offers excellent image quality, but because of the thick corrector lens (heavy and expensive), Maks rarely exceeds 7 or 8" in an amateur instruments. The Scmidt-Cassegrain, commonly known as an SCT, uses a thinner corrector plate (lighter and less expensive) and is made in very large sizes. Thus, an 8" SCT offers enough resolution for serious planetary work, but also enough size for serious deep-sky work. Thus the SCT is the best choice going for an all-around telescope which accounts for its tremendous popularity.
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