|Understanding the telescope and choosing the best one for you|
Purchasing a new telescope can be baffling, especially for the first timer. And most of us are left wondering, so which telescope is for me? Understanding telescopes and their various accessories can go a long way in choosing the best one for you. Whether you are an amateur astronomer or veteran pathfinder, here are a few basic ground rules that will help you better identify the different types of telescopes and help you opt for the ideal one for you.
Aperture of a telescope
Aperture of a telescope
A telescope's most important attribute is its aperture, which determines the brightness and sharpness of everything you see through your scope. Technically, this is the diameter of the main lens or mirror and as the aperture increases so does the details of the image you see. Depending on the aperture you will either see an open or a restricted field of view. For example a good 10" aperture scope shows sharper images than even a well-made 6" aperture telescope.
Ask yourself, where will I want to use my new telescope? If the answer is nearby in the backyard then having a large telescope will be of advantage to you. If you need to carry the telescope to darker skies away from city lights, you will definitely need something compact, yet powerful. And don't forget that you may have to assemble and set up your telescope in the dark making it even more difficult. And a scope that is too huge to carry outdoors and too long-drawn-out to set up, will rarely be of use.
Power or Magnification of a telescope
Power or Magnification of a telescope
Keeping aperture in mind, consider other important aspects like power and design before you make up your mind about the telescope you would like to purchase. Power is the magnification that the telescope can offer. This is a critical factor since it decides how close a view you can get of the space and planets. But it is not a decision making factor. You can make any telescope magnify at effectively any power you want by using different eyepieces.
An eyepiece is the small removable lens assembly you look into. Most telescopes come with several eyepieces and you can buy more separately. Remember to match the power of your eyepiece lens with the aperture of your scope for clear images. Using a very high power lens with a small-aperture telescope will show a highly magnified fuzz while with a large-aperture scope can show a meaningful image even at 200x or more. In either case, the lowest powers are the easiest to use, especially for beginners, and provide the most pleasant views.
Designs of Telescopes
Even among telescopes with the same aperture, some designs are more portable, others give sharper images while still others are more economical. There are three basic kinds of telescope to choose from depending on your specific requirements
All these 3 telescopes have the same light-gathering properties, despite their differences in size and weight. They also have a similar purpose, to collect light and bring it to a point of focus so it can be magnified and examined with an eyepiece, but each does it differently. Consequently, each type of telescope has its pros and cons, which you can match with your observing needs.
1. The refracting telescope or refractor
Refractors are the most common form of the telescope - a long, thin tube where light passes in a straight line from the front objective lens directly to the eyepiece at the opposite end of the tube.
2. The reflecting telescope or reflector
Reflectors use a huge concave parabolic mirror instead of a lens to gather and focus the light to a flat secondary mirror that in turn reflects the image out of an opening at the side of the main tube. You look through an eyepiece on the side of the tube up near the top.
3. Catadioptric telescope
Catadioptrics use a combination of mirrors and lenses to fold the optics and form an image. Catadioptrics are the most popular type of instrument, with the most modern design, marketed throughout the world in 3 ' and larger apertures. There are two popular designs, the Schmidt-Cassegrain and the Maksutov-Cassegrain.
In the Schmidt-Cassegrain, light enters through a thin aspheric Schmidt correcting lens, then strikes the spherical primary mirror and is reflected back up the tube to be intercepted by a small secondary mirror. The mirror then reflects the light out an opening in the rear of the instrument where the image is formed at the eyepiece.
The Maksutov-Cassegrain telescope design has basically the same advantages and disadvantages as the Schmidt. It uses a thick meniscus-correcting lens with a strong curvature and a secondary mirror that is usually an aluminized spot on the corrector. The Maksutov secondary mirror is typically smaller than the Schmidt's giving it slightly better resolution for planetary observing.
However, the Maksutov is heavier than the Schmidt and because of the thick correcting lens, it takes a long time to reach thermal stability at night in larger apertures. The Maksutov optical design typically is easier to make but requires more material for the corrector lens than the Schmidt Cassegrain.
Now that you have learned about aperture, power and the different types of telescopes, let us discuss an often overlooked but very important aspect of using a telescope - the mountings. Remember that shaky view is all it takes to kill your enthusiasm! And a good mount can enhance your views. There are two basic telescope mountings:
The equatorial and the altazimuth.
An Equatorial mount is designed so you can easily track the motion of the sky as the Earth turns and its motions indicate celestial north south and east west in the eyepiece. This is a great help when you're trying to find your way among the stars with a map. The Altazimuth mounts are simpler and just swing up, down, left and right. You have to move the scope along every so often to follow the stars, moons and planets. An altazimuth mount is both cheaper and lighter for the same degree of stability, advantages that are offered by an equatorial mount design.
About the Author
Gary Sharma is a successful freelance writer offering guidance and suggestions for consumers regarding how to choose the best telescopes, spotting scopes and binoculars for your needs. His many articles give information and tips to help people save money and make smarter decisions.