TELESCOPES

An Introduction

If you're involved in amateur astronomy for any amount of time, you'll start getting interested in a telescope.

These days, there are a number of different types, along with different mounts. We'll explore each of these.

Refractors

Refractors are the oldest type of telescope. They feature a primary, or objective, lens up front, and an eyepiece at the viewing end. You can kit it out with numerous accessories (image erectors, right-angle viewers, finderscopes), but the main design of big lens, little lens, and a shape similar to a baseball bat, usually are the giveaways.

Reflectors

Reflecting telescopes have been around for hundreds of years, in various sub-types. Generally, a reflector can be recognized through its usually more-squat shape, and often the placement of the eyepieces.

Newtonian Reflectors

This sort of telescope, invented by Sir Isaac Newton, features a primary mirror at the end of a long tube. The mirror reflects light back up towards a small secondary mirror, canted at a 45-degree angle, and out the side of the telescope. You can usually spot a Newtonian telescope by the placement of the eyepiece; if they're near the front, it's probably a Newtonian.

Cassegrain Reflectors

This sort of telescope, often referred to as a Catadioptric Telescope, features a mirror mounted flush; the light is bounced off the parabolic primary mirror, up to the secondary mirror, and back down and out through a hole in the primary mirror.

Schmidt-Cassegrain Reflectors

These are similar to cassegrains, except that a correcting 'lens' up front combats spherical aberration. The primary mirror may also be spherical.

Maksutov Reflectors

These are similar to Schmidt-Cassegrains, but the nature of the correcting lens is a little different. Adherents swear by it.


MOUNTS

The telescope mount is just as important as the type of telescope. Again, there are several mount types:

Alt-Azimuth
This is a simple up/down, left/right kind of mount. It's usually the cheapest, and with the advent of computer-controlled mounts, they are much more useful.

Equatorial
This is a more-complicated version, best described as an Alt-Az mount which itself is mounted on a wedge that corresponds to the local latitude. This has the effect of 'tilting' the mount to match the sky; circles in the azimuth will correspond to latitude circles in the sky. This type of mount is unwieldy on larger telescopes.

Dobsonian
This is an exceedingly simple type of mount, usually applied to reflectors more than refractors. Basically, it two arms which come up from a circular, rotating base; each 'arm' cradles a short arm extending from the telescope. This allows the telescope to be moved in altitude and azimuth, manually. Some have turned their 'Dobs' into de-facto equatorial mounts by putting them on a wedge (and taking great care to balance the instrument).

Most people cut their teeth on something like a 60-mm refractor, often on an alt-az mount. I have one of those. I also have one on an equatorial mount; and a four-inch reflector on what I can only describe as a 'bowl-mount'.

If I can offer one piece of advice: don't buy your first telescope at a camera shop or department store. Those tend to be underpowered, overpriced, and on cheap, rickety alt-az mounts. Take some time to peruse Internet ads for telescopes and mounts; it'll give you a feel for the prices of various types of instruments, plus a decent mount. Watch out for "200-power" and "400x" telescopes; generally, magnification that high is useless for astronomical viewing; and if that's what they're emphasizing, you don't want their product.

Have fun! Till next time,

-Bill