Things To Consider When Buying A Telescope?
What are you going to use it for?
Most people are under the impression that it doesn't matter what telescope they buy, under the assumption that all telescopes are excellent for both sky and land. The truth is, no matter how attractive the thought of an all round telescope is, the common rule is that land based viewing telescopes rarely excel for astronomy, with the same applying to telescopes for sky viewing.
If you are more interested in land viewing perhaps a good set of binoculars may be of better use.
Knowing the main use will also help you to shop within your budget by enabling you to determine whether a cheaper option might be more suitable..
Power - A good scope will not talk about its magnification or power: If the box blares "300X" or other numbers about the power the scope within has, proceed with Caution! High power sounds great, but there's a catch. While high magnification makes an object appear larger, light gathered by the scope is spread over a larger area creating a fainter image. The magnification of your telescope is determined by the eyepiece you use. Changing magnification just involves swapping your existing eyepiece with one that has a higher magnification. Essentially any telescope can have an infinite range of magnification. So don't get too excited by telescopes that promote a large magnification.
Aperture size is the true key to the "power" of a telescope: The aperture of a scope refers to the diameter of either the objective lens of a refractor or objective mirror of a reflector. Its ability to gather light is directly proportional to the size of its aperture and the more light a scope can gather, the better the image you will see. Typically, 2.4 inch (60mm) and 3.1 inch(80mm) refractors and 4.5 inch and 6 inch reflectors are popular for most amateurs.
The main types of scopes and their uses
1. Refracting Telescope or Refractor
Refracting telescopes are the probably the most common telescope around. They use lenses instead of mirrors and the eyepiece is located at the bottom of the telescope. Their design is similar to binoculars and most spotting scopes. It should be noted that images from refractors are mirror images and can be corrected using an erecting prism. For beginner's this doesn't have a large effect on your viewing experience. vantages
- Easy to use and consistent due to the simplicity of design.
- Excellent for lunar, planetary and binary stargazing especially with larger apertures.
- Sealed tube protects optics and reduces image degrading air currents.
- Rugged, needs little or no maintenance Disadvantages
- Generally have small apertures, typically 3 to 5 inches.
- Smaller apertures mean poorer viewing of distant galaxies and nebulae.
- Heavier, longer and bulkier than reflector and cassegrain telescopes of equal aperture.
- Good-quality refractors cost more per inch of aperture than any other kind of telescope.
2. Reflecting Telescope or Reflector
Reflexting Telescopes use a mirror, instead of a lens, and the eyepiece is located at the side of the main tube. You look through an eyepiece on the side of the tube up near the top. Advantages
- Usually have larger apertures which mean excellent viewing of faint deep sky objects (remote galaxies, nebulae and star clusters).
- Low in optical irregularities and deliver very bright images.
- A reflector costs the least per inch of aperture compared to refractors and catadioptrics since mirrors can be produced at less cost than lenses.sadvantages
- Generally, not suited for terrestrial applications
- The tube is open to the air, which means dust on the optics even if the tube is kept under wraps
- Reflectors may require a little more care and maintenance
3. Cassegrain or Catadioptric telescopes
CatadiotropicÂ or Cassegrain Telescopes, use a combination of mirrors and lenses. These telescopes usually have a nice modern design and have 3" and larger apertures. Two of the popular cassegrain designs are the Schmidt-Cassegrain and Maksutov-Cassegrain.Advantages
- Most versatile type of telescope with excellent lunar, planetary and deep space observing plus terrestrial viewing and photography.
- Best near focus capability of any type telescope
- First-rate for deep sky observing or astrophotography
- Closed tube design reduces image degrading air currents
- Compact and durable Disadvantages
- More expensive than reflectors of equal aperture
- There appearance may not be suited to everybody's taste
A stable mount is always a good thing
A mount is important for stabilising your telescope and determining how easy it is to follow a star.
There are two basic telescope mountings:
- Equatorial Mount
- AltAzimouth Mounts
An Equatorial mount, simply put, allows users to follow the rotation of the sky as the Earth turns. This is a great help when you're trying to find your way among the stars with a map. These usually cost a bit more but it is highly recommended.
The Altazimuth mounts in contrast have a simpler design, meaning they just swing up, down, left and right. You have to move the scope every so often to follow the stars, moons and planets as the earth turns. An altazimuth mount is both cheaper and lighter for the same degree of stability but it misses out on the ability to easily follow the rotation of the sky when the earth turns.
Remember: Always Make A Decision Based On Your budget