The Cassegrain Telescope

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  2. March 24, 2014 1:53 am

The Cassegrain Telescope

The Cassegrain telescope is named after its inventor, Laurent Cassegrain, who came up with the design in the late 1600’s. A Catholic Priest and professor, he published the design which solves the problem of mirror obstruction. There are many variations on the design today with the Schmidt-Cassegrain being one of the most popular.

The Cassegrain telescope is of the reflector type. Its design allows light to enter through a tube and strike a primary mirror which reflects it back to a convex secondary mirror. The light is then reflected to a hole in the primary mirror which houses the lens.

The Cassegrain telescope has a “folding” effect. It can use a shorter tube while giving a greater focal length due to light being reflected from the primary mirror to the secondary mirror and back to the eyepiece. Focal length is the measurable distance of how far light travels in the telescopic system to converge or diverge on the lens. Greater focal length leads to greater magnification and resolution of the telescope.

A large advantage of the Cassegrain is its size and portability. The short tube of the Cassegrain accomplishes as much as a Newtonian reflector more than twice its length due to its “folding” capabilities. Its resolution qualities make it a favorite with astronomers who wish to observe the moon and its features or the closer planets, such as Jupiter and Saturn.

An 8” or larger Cassegrain telescope will provide its observer with details of the Jupiter surface, such as bands, and give a crisp appearance to the rings of Saturn. A look at the moon will reveal sharp edges to the mountains and ledges of the craters. Its large primary mirror also allows for excellent viewing of deep sky objects such as nebulae, galaxies and clusters.


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