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Advantages and Disadvantages of Reflectors

A little known choice one can make when purchasing a telescope is to decide between a reflecting and a refracting telescope. Refracting telescopes are the more commonly known type which use a pair of lenses to focus and magnify light for the human eye, while reflecting telescopes use a set of curved mirrors to focus light, which is then sent to the human eye. While the net result is the same (a larger, clearer image), there are various benefits and drawbacks to both. For the purposes of this article, we shall discuss the reflecting telescope.

As mentioned earlier, the reflector telescope uses a concave mirror to collect and concentrate light, which is then reflected off a second mirror and into the eyepiece. This system has several advantages. The first and most important advantage is that reflector telescopes are cheaper than refractors; the latter can cost up to five times as much as the former. This is because refractor telescopes need to have their lenses painstakingly machined in order to achieve good optics. Secondly, due to the vagaries of the lens shaping process, refractor lenses are prone to aberrations, which may distort the image and color of the image obtained. Reflectors do not suffer from such drawbacks, and tend to produce a brighter and clearer image than refractors. In addition, since the objective mirror (the one which collects light) is usually firmly backed on the entire surface of its rear by the telescope assembly, they can be made larger without compromising structural integrity. Finally, because reflector surfaces are lighter than lenses of a comparable aperture, they weigh less and are easier to manipulate than a refractor telescope of comparable size.

However, reflector telescopes have their own share of disadvantages. The most critical flaw they have is that they require regular maintenance; for instance, the mirrors of a reflector telescope must be regularly recoated in order to preserve their reflective ability. Refractors do not require similar treatments. In addition, the optics must be regularly collimated (realigned) for best performance. Failure to perform adequate collimation will greatly impair the quality of the telescope’s image. As the reflector telescope has an open assembly, it is easier for dust and other contaminants to settle on the telescope, which in turn requires more maintenance to be done. Finally, a reflector telescope is nowhere as secure and sturdy as a refractor telescope; odds are a reflector telescope will not be able to survive even light, accidental impacts without requiring a re-alignment of the mirrors.

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