Telescopes: Bringing Objects within Viewable Distance
When a person wishes to view objects that are at a distance, one may need to use an instrument known as a telescope that is specially designed to facilitate such a requirement and bring objects close enough to be viewed through an eye lens on it. Mostly, one would refer to it as an optical instrument though there are other similar instruments that are used for the spectrum of electromagnetic radiation as well as for other signal types. The history of this instrument can be traced back to the Assyrian crystal lenses, but the Visby lenses seem to imply that such a technology was in the knowledge of Arabs as well as Persians as well. One can ascribe the invention of this instrument to a person named Leonard Digges who assembled the first such instrument in England in the 1570s though it is also ascribed to an obscure Dutch spectacle maker in 1608.
The aim of this optical instrument is to focus visible light as well as other electromagnetic radiation and increases the angular size of far-off objects and also their perceptible brightness. It will use one or more curved optical elements such as lenses or mirrors to collect light and bring it to a focus and allow the viewer to observe, photograph or study the image.
Optical Telescopes
Optical telescopes can be used in astronomy as well as in non-astronomical instruments such as theodolites, transits, spotting scopes, monocular, binoculars, camera lenses as well as spyglasses. There are other types of such instruments including the Radio telescopes that focus radio antennae, and the X-ray and gamma-ray telescopes. These instruments are often characterized by their designs and are named after their designers. There are three such optical instruments, most particularly used for astronomical purposes, and these are refracting, reflecting and catadioptric telescopes.
The reflecting instrument uses only an arrangement of lenses while the reflecting ones uses only mirrors, while the catadioptric telescopes use a combination of mirrors and lenses. For direct viewing with the human eye, one may use a telescope that mostly would not be of a reflector type, because it is normal for one to use an eyepiece for viewing the image, and thus requires an arrangement of lenses, which is the case with refracting instruments.
In the case of telescopes used for astronomy, viewing is performed with the help of photographic film or digital sensors, and they normally do not require an eyepiece and so are usually reflector telescopes. There are also research telescopes that are either a Cassegrain or a Newtonian telescope. With the Multiple Mirror Telescope, a new era in this type of instrument has arrived, and with more research, there will be many others added such as imagers, spectrographs, and polarimeters. And, new technology is also coming to terms with overcoming distortions caused by atmosphere on such ground-based instruments.
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