Schmidt-Cassegrain Telescopes

A Brief Introduction on Cassegrain (or Catadioptric) Telescopes

The Cassegrain telescopes (or catadioptric telescopes) use both mirrors and lenses that fold the light path, allowing a shorter tube length. The basic design, invented in the late seventeenth century by Laurent Cassegrain, combines the long focal length of a refracting telescope with the lower cost per aperture of a reflecting telescope. Cassegrains are very compact and portable for its given aperture. With high f-ratios, they are not a wide field telescope but are good for more narrow field, deep sky and planetary viewing.

Schmidt-Cassegrain Telescopes (SCT)

In the SCT system, the parabolic primary mirrors common in Newtonian reflectors are replaced by spherical mirrors, which introduces spherical aberration. This is then corrected by the Schmidt corrector plate to ensure sharp images. The Schmidt-Cassegrain telescope is supported by a wide range of accessories for both observation and astrophotography applications.

Below are some great Schmidt-Cassegrain telescopes to have!!

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NASA Image Of The Day

Snapshot of the International Space Station

On March 13, 2008, the International Space Station passed across the field-of-view of Germany's remote sensing satellite, TerraSAR-X, at a distance of 195 kilometers, or 122 miles, and at a relative speed of 34,540 kilometers per hour, or more than 22,000 mph. In contrast to optical cameras, radar does not 'see' surfaces. Instead, it is much more aware of the edges and corners which bounce back the microwave signal it transmits. Smooth surfaces such as those on the station's solar generators or the radiator panels used to dissipate excess heat, unless directly facing the radar antenna, tend to deflect rather than reflect the radar beam, causing these features to appear on the radar image as dark areas. The radar image of the station therefore looks like a dense collection of bright spots from which the outlines of the space station can be clearly identified. The central element on the station, to which all the modules are docked, has a grid structure that presents a multiplicity of reflecting surfaces to the radar beam, making it readily identifiable. This image has a resolution of about one meter (about 39 inches). In other words, objects can be depicted as discrete units--that is, shown separately--provided that they are at least one meter apart. If they are closer together than that, they tend to merge into a single block on a radar image. Since this image was taken, the station has expanded and is more than 90 percent complete, including a full complement of solar arrays. Image Credit: DLR
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Schmidt-Cassegrain Telescopes

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