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Telescopes - research into types and properties of telescopes

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Telescopes are instruments that magnify distant objects. Astronomers use telescopes to study the planets, stars, and other floating bodies. In most telescopes a lens or mirror is used to form an image of an object. The image may be viewed through an eyepiece or recorded on photographic film or by electronic devices. Telescopes produce images of objects too far away to be seen by the unaided human eye. The Dutch optician Hans Lippershey designed the first telescope in 1608, when he mounted two glass lenses in a narrow tube. Within a year the Italian astronomer Galileo built a similar device and became the first person to use a telescope to study the sky.

Optical Telescopes

Optical Telescopes use a lens or mirror to collect and focus light waves. There are three main types of optical telescopes.

Refracting telescope

Refracting telescopes also known as refractors have a large lens called an objective lens at one end of a long, narrow tube. The lens is convex on both sides so that the middle of the lens is thicker than the edges. The glass slows the light rays as they pass through the lens.

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Astronomers generally prefer reflecting telescopes to refracting telescopes. The weight of a large lens can cause it to bend and become distorted. But a large heavy mirror can be supported from behind. As a result mirrors can be made much larger than lenses, and therefore can gather more light. In addition, parabolic mirrors are useful because they can collect infra red and some ultra-violet rays’ as well as visible light. Reflector telescopes also do not suffer from chromatic aberration, as all the wavelengths will reflect off the mirror in the same way. Also only one side of the reflector telescope needs to be made perfect as the light is reflecting off the objective.

However it is easy to get the optics out of alignment. Often a secondary mirror is used to redirect the light into an eyepiece. This secondary mirror produces diffraction effects, making bright objects appear to have spikes.

Isaac Newton designed one of the first reflectors in 1668 to avoid chromatic aberration caused by lenses. In his design, Newton used a small, flat mirror to reflect light from the primary mirror to an eyepiece at the side of the telescope tube.

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Modern Developments in Telescopes

Several Breakthroughs in mirror designs have enabled astronomers to make large mirrors that do not bend or become distorted under their own weight.

One new design is the segmented mirror, used in the Keck telescope (completed in 1992) on the island of Hawaii. The Kecks light-gathering mirror consists of 36 hexagonal mirrors mounted close together. The mirrors form a reflecting surface 10 metres in diameter.  

In conclusion I personally believe that reflecting telescopes would be the best option to invest in. As refracting telescopes suffer from Chromatic aberration, and Catadioptric telescopes due to their more complex design cost a fair deal more then reflecting telescopes.  Catadioptiric telescopes also lose some light due to the secondary mirror obstruction. Which intern can result in a less visible image.

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