How to Choose the Right Telescope

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Ever been interested in space and the night sky? Well, these steps will start you off on a great adventure.


  1. The diameter of the objective lens or mirror is the most important number describing a telescope. Larger diameter lenses or mirrors allow higher resolution (ability to separate closely spaced objects) and will gather more light from faint astronomical objects. They also cost more.
  2. Magnification is relatively unimportant and is often hyped in advertising claims for inexpensive telescopes. In astronomy, the purpose of a telescope is mostly to collect light from faint objects, not to magnify them.
  3. Too much magnification just gives you a useless blur. A good rule of thumb to determine the maximum usable magnification is to multiply the diameter of the objective in millimeters by 2.5 (which means that the typical department store 60mm scope is only usable to 150x). In actual practice, on nights of extremely unusual atmospheric stability, you -may- be able to use a somewhat higher power, but do not count on it.
  4. The better eyepieces have larger "eye relief," which represents how close you have to get your eye to the eyepiece to observer clearly. If the eye relief is too small you will have to bring your eye very close to the eyepiece, and it will be all but impossible to observe for more than a few seconds at a time.
  5. Look for a steady mounting, an unstable or shaky mounting will ruin your observing experience. In general, the more massive the mount looks, the better it performs. When in doubt, spend more on a mount.
  6. Join an astronomy club and learn to use someone elses telescope before buying your own.
  7. Start with a pair of binoculars and learn to find things in the sky before buying a telescope.
  8. Do not expect a small telescope to show the same images that you see in astronomy textbooks, which are usually long time exposures and may have been taken by much larger professional grade telescopes.


  • For best results, look through a telescope in a dark place. In a city, you are not going to see much. There are special eyepiece filters available to help reduce light pollution from streetlights, but they are not dramatically effective and are expensive.
  • Consider getting an auto star telescope -- it will find things for you to look at and prevent you from endless searching. Even with these "GoTo" scopes, you still have to be careful in leveling the tripod and picking the right bright stars to perform alignment on. You typically have to choose two or three bright stars to align on so that the telescope knows where on Earth it is situated.
  • Try to get a reflector telescope for best viewing -- a refractor is fine as well. Reflector telescopes are much cheaper for a given objective size, but to perform at their best they require regular collimation--making sure the internal mirrors point perfectly straight down the tube. There are special eyepieces (called "Cheshire" eyepieces) that are inexpensive and make collimation much easier.
  • Contact your local planetarium if you have further questions about buying a telescope. They will be happy to guide you to local and mail-order dealers who are reputable.
  • Do not buy a $200 eyepiece to get a higher power, instead, spend it on a better scope.
  • Warnings

    • Never look at the sun with a telescopes or binoculars. You may blind or severly damage your vision for the rest of your life by doing so.

    Things You will Need

    • Telescope
    • accessories (eyepieces, filters, etc.)

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