subject: Independant Guide For Reflector Telescope Buyer. [print this page] Reflector telescopes use a mirror to collect and focus light emanating from celestial objects including those from our own solar system. Since these objects or stars are very far away from you, the light rays reaching the earth and your telescope are parallel. These fall on the mirror inside your telescope which has a parabolic profile and this helps in reflecting the rays to a single point. Hence they have the name reflector telescope. In addition, in contrast to Skywatcher refractor telescopes, they do not suffer from chromatic aberration (distortion in color) since all wavelengths get reflected from your mirror equally. Apart from this, reflector telescopes have the advantage of being made in big size, they are less expensive than refractor telescopes of same size and since light is reflected rather than passing through, only one side need to be optically perfect. However, they also have some disadvantages. The optics may get misaligned and they need frequent cleaning. Also, where secondary mirrors, either curved (convex) or plain, are used they may produce glare triggered by bright stars.
Just before you determine which telescope to buy, remember that larger the size of the light gathering source called the aperture, better is the object resolution or finer details are now visible. In other words any 304mm (12 inch) is better than a 155mm (6 inch) telescope! Usually a reflector telescope with 114 mm (4.5 inch) is adequate to watch the moon, planets in our solar system, sun with special filters to protect your eyes and some stars in the nearer galaxies. Most renowned models are 60mm (2.4 inch), 80mm (3.1 inch), 114mm (4.5 inch) or 155mm (6 inch). Be aware also that larger aperture will also mean heavier telescope minimizing its transportability.
Perhaps you have noticed ads for reflector telescopes offering power as 300X or so. Well, more power does not mean better viewing, since the power refers to the magnification and may give larger, but very faint image. Also, the small eye-piece may not allow you to see the entire of the image due to size restriction. Hence do not get carried away by these terms. What is essential is to get the best aperture and eye-piece combination for the best viewing pleasure.
There is yet another term some manufacturers use to push their product. This is the focal ratio or the ratio of aperture size to focal length. For example a telescope with 114mm (4.5 inch) aperture and 1143mm (45 inch) focal length has focal ratio of f10. Higher focal ratio does not always mean higher image quality. Also larger ratio with similar aperture would mean a longer telescope.
Mount is crucial for steady viewing. There are two types of mounts offered; altazimuth or equatorial. Altazimuth is like a photographic camera tripod permitting movement up and down (altitude) and back and forth (azimuth). Equatorial mounts, at times with drive motor, are best for following an object in its revolution and travel. The last item to watch out for is the eye piece. Some models offer several eye pieces (two or more) so that your close friends can also watch at the same time. Power of the eye piece is expressed in mm and most popular is 25 mm; lower its number, better is the magnification.
by: Leo Barus
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