"The universe is like a safe to which there is a combination, but the combination is locked up in the safe."
- Peter de Vries

Markarian's Chain (Bob Long)

Telescope Basics

Observing Basics


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Telescope Basics

Mounts (what are you going to put that telescope on?)

Equitorial MountTelescopes can be placed on a variety of mounts. The simplest (and least expensive) swivel and rock much like a cannon is aimed. These alt/az (or Dobsonian) mounts are very easy to use. Many have built-in computers that can automatically and accurately point your telescope to various objects in the sky. Alt/Az mounts are not well suited, however, for doing most types of astrophotography.

Equitorial mounts align the telescope with the Earth's tilt, and are thus the choice for astronomers wishing to take photos. Good equitorial mounts can be very expensive. They are not, however, ideal for observing as they can place the observer in some very awkward positions. Again, Computer-assisted GoTo capabilities are available (often at an additional cost). A sturdy tripod or pier is also needed for doing imaging.

Eyepieces (and just a little math)

eyepiecesPeople often ask how powerful a telescope is. Magnification is a function of a scope's focal length (usually between 500 and 3000 mm) and the eyepiece's focal length (usually between 4 and 40 mm). Divide the scope's focal length by the eyepiece's focal length and you get magnification. An 800 mm scope with an 8mm eyepiece achieves the same magnification (100x) as a 2500 mm telescope with a 25mm eyepiece.

Interestingly, most astronomers observe at magnifications between 50 and 150 power (even though their scopes might be capable of much higher magnification). Don't be tempted by some manufacturers' claims of their telescope's ability to magnify 500 or 600 times. While technically a true statement, the image at 500 or 600 power will be of very poor quality.

Consider Used Equipment

Unless you just have to have a brand spanking new telescope or mount, consider purchasing equipment. Unlike used cars, telescopes, eyepieces and mounts tend to wear very well if they're well cared for - and most owners of quality telescopes take excellent care of their equipment. Occasionally, equipment shows up on eBay, but most telescope owners sell their equipment on either or You'll likely save 20-30% off the new price - and - you'll probably be able to use the equipment, then sell it for nearly what you paid for it. Telescopes of all designs and price ranges are available as well as mounts, eyepices, filters, cameras, etcetera.

Want More Information??

Nils Allen, ASLC's educational guru, has prepared two more detailed documents on selecting and using a new telescope (both are in pdf format).

Telescope Buying Advice (96k)         Using Your New Telescope (76k)

And if that's still not enough, click here for a website with links to tons of information about telescope optics.