What are the Two Types of Telescopes?

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By Nannette Richford
eHow Contributing Writer

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Telescopes are divided into two basic categories: reflectors and refractors. Both gather and focus light to magnify images. The reflector telescope is designed with a concave primary mirror at the bottom of the tube that reflects light onto a flat secondary mirror and brings the image into focus in the eyepiece. The refractor telescope uses a convex lens that refracts parallel rays of light into a single focal point, magnifying the image in that is viewed in the eyepiece.

History

In 1608, Jassen, Lipershey and Metius invented the first refractor telescope. In 1611, the use of a convex lens as an eyepiece was invented by Johannes Kepler. In 1733, Chester Hall invented the achromatic lens by creating a lens made of two pieces of glass that were assembled together. The first reflector telescope appeared in the early 1600s. In 1668, Sir Isaac Newton designed the reflector telescope with the use of two mirrors inside a hollow tube to gather and focus light into the eyepiece.

Function

The refractor telescope is ideal for viewing distant celestial objects. Although the image is inverted when viewed through the eyepiece, this is of little consequence for celestial viewing. It is the preferred scope for deep sky viewing of remote objects like galaxies and star clusters. It is also a good scope to use for astrophotography.
The reflector telescope is ideal for viewing the moon or planets and other closer objects.

Features

Advantages of the refractor telescope are that it requires little care and is easy to use, has good image clarity with good color, has a sealed tube that prevents imaging degradation due to air currents and provides protection for the optics inside the tube, and the lens is aligned and mounted permanently.
Advantages of the reflector are that it is compact, portable and produces clear, bright images.

Considerations

The refractor telescope is more expensive than a reflector, is larger and bulkier than a reflector, suffers some color distortion and is limited to smaller apertures within a reasonable price range.
The reflector telescope requires adjustment to the optics to maintain the best quality, mirrors may require re-coating periodically to maintain quality, it is complicated to clean and maintain, and it's not suitable for viewing terrestrial objects.
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Misconceptions

Many erroneously believe that purchasing a telescope with a high magnification will provide a better image and allow them to view distant objects clearly. Because the amount of light gathered determines to a large part how well you will see an image, the size of the aperture is actually more important than the magnification of the lens. The aperture of a telescope is the size of the opening at the end of the tube that allows light to enter the scope.