Telescopes for the Amateur Astronomer
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by: DavidWildash
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Binoculars with a strength of 7 X 35 can actually be a better choice than a telescope. Binoculars are more portable and convenient, relatively inexpensive, and it's wiser to get cheap binoculars over a cheap telescope. With the 7 X 35 binoculars, the first number stands for the eyepiece magnification and the second number is the aperture in millimeters. Binoculars of this caliber are lighter and easy to hold.
There are three types of telescopes available for beginning astronomers.
Refractors consist of lenses at both ends, and the most recognized type of telescope. They generally cost more per aperture inch than other telescopes, but their size makes them ideal beginner telescopes. It's best to avoid cheap department store models, as these quote large magnifications but have small, useless apertures. The job of a telescope is to collect an images light, not magnify it, so large magnifications actually make things worse and can alter data. Earthly telescopes usually have extra lenses to make an image appear right side up, but this extra lense can cut down the amount of light that reaches the eye. Therefore, the extra lense is left out of astronomical telescopes, which leaves images upside down. Since lenses can create false rainbow images around really bright objects, it's best to buy a filter to help correct the problem.
The second type of telescope is the reflector. Light travels down a tube before reflecting off a couple of mirrors and through an eyepiece on the side of the tube. Reflectors need to be larger than a refractor to be equally useful. They do not suffer chromatic aberration, but the main mirror may occasionally need repolishing or realigning (collimating). There are kits available for this. Reflectors are often the most comfortable telescopes to use because of the eyepiece position. You don't have to kneel and possess an elastic neck to look straight upwards as you would with a reflector. A popular type of reflector is the Dobsonian, which has a mount near the ground rather than a tripod.
Finally, there is the Schmidt-Cassegrain telescope. This telescope uses both lenses and mirrors to fold light back onto itself inside a compact tube. These cost less than refractors and are dearer than reflectors, and are overall more portable and easier to handle.
Telescope specifications may quote numbers.These have no affect on the image you see, but can affect the exposure needed if you get into astrophotography. It's best to avoid astrophotography to start with. Become familiar with the sky and your telescope first.
By joining a local astonomy club or checking a library, you can evaluate different types of instruments. Also, astronomy magazines have reviews as well as advertising for good telescopes.
Even though you should purchase the largest aperture you find, keep in mind you may not want a large telescope as you may have to carry it around. Smaller telescopes are easier to set up and use, and high pollution in your area can keep a large telescope from producing results to its full potential.
It's best to spend most of your money on a buying a large aperture instead of telescope accessories. Doubling the aperture number will calculate the maximal practical magnification: i.e., a 70mm aperture will have a maximum magnification of 140x. Do not buy an eyepiece that is stated to stretch magnification past maximum aperture value. Start simple with eyepiece choices, such as a Kellner, which is a good all around eyepiece. If you place a Barlow lens between an eyepiece and focuser, magnification can be tripled.
Along with finding celestial objects, telescopes also follow the movement of those objects. The instrument must be moved repeatedly to keep the object in focus, and different mounts and drives make this possible. Electronic drives will point a telescope in the right direction, but the sturdiness of the mount is the most important thing.
It may be saddening to know that many textbook photos have false colors and are long exposures. The eye is not sensitive enough to see color in dim objects, and stars will always look like tiny light points.
So what can you expect to see with a beginners telescope? A 3-inch (75mm) refractor or 6-inch (150mm) reflector will allow you to see many galaxies and nebulae, Saturn's rings, Jupiter's largest moons and hundreds of craters on the moon. Plenty of wonderful objects to serve as an introduction to the night sky.
About the Author
David Wildash posts information and tips on his website about Telescopes , and you can read more about buying a telescope
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