A mount really isn't an accessory, per se. It's a necessity unless you enjoy shouldering your telescope like a bazooka.

What about those groovy U-shaped fork mounts? (I'm glad you asked.) The classic fork mount that you see holding those glossy Schmitt-Cassegrain telescopes (the folded optical design mentioned in past story) actually has a dual identity. It qualifies as an altazimuth mount when its axes are oriented toward the horizon (altitude and azimuth motion). But angle one Axis -- the one located in the valley of the U -- toward the celestial pole and voilà, you have an equatorial mount.

The advantage in having an equatorial mount is that you can attach a motor, or clock drive (see below), to the polar axis and automatically track the stars as they drift across the sky. If you want to get into long-exposure astrophotography, an equatorial mount is a "must have."

Both altazimuth and equatorial mounts may also be fitted with "slow-motion" controls. These simply allow the user to move the telescope incrementally in either axis by manually turning a knob or cable. These come in handy when you want to make small adjustments to positioning an object in the field of view.

Telescope manufacturers sell equatorial mounts with and without drive systems, although the more expensive models usually come equipped with one.

Is a clock drive a "must-have?" Only if: a) you find it bothersome to continually nudge the telescope to keep a star or planet from drifting out of the field of view or b) you plan to use your instrument for astrophotography. It's not an absolute necessity otherwise. So I put a clock drive into the "sooner-or-later" bin for those owning equatorial mounts.

In addition to a clock drive, you can also purchase a guiding system. This allows you to make incremental adjustments to the tracking speed in the polar axis (a single-axis guider) or both the polar and declination axes (a dual-axis guider). This may be more of a "later-than-sooner" item, since it mainly benefits astrophotographers.

I must admit that I am somewhat of a Luddite when it comes to embracing the computer automation of recreational telescopes. Still, there's no denying that a lot of amateur astronomers are excited by this latest techno-innovation and they can't all be wrong -- can they? Nevertheless, I put this into the "luxury" category.

Advertising jargon for computer drives refers to them as "go-to" or "auto-align" systems. Essentially, an on-board computer points your telescope for you. All you have to do is decide which object to look at. And you have plenty of choices too, if you consult widely available databases of coordinates for tens of thousands of galaxies, star clusters, nebulae, bright asteroids and periodic comets, not to forget double, multiple and variable stars.

They'll even find the planets for you, in case you can't recognize them in the sky.

Set up is fairly straightforward. Usually you align the telescope on two stars that the computer recognizes. (One model even finds the two alignment stars for you!) After that, you're free to roam the universe.

Another attractive feature of these robotic drives is the ability to control your telescope from your personal computer. For example, using a compatible astronomy software program, you can find an object on the screen that you want to observe, select it and the telescope will find it for you.

The price for these robotic telescopes is a lot less than you might think, but they don't come in a wide variety of sizes. The two major North American telescope manufacturers, Meade and Celestron, offer models with apertures from 4 to 8 inches (10 to 20 centimeters). No doubt larger sizes are in the offing, but they will be correspondingly more expensive. Still, the attraction of having your telescope do everything but your income tax may more than compensate for lack of aperture.

There is yet another device available that is neither a clock drive nor a computer drive. Basically, it's a manual sky-guiding unit containing a database of thousands of objects. But rather than find your target for you, it directs you to your quarry using arrows on its LED display.

It's a little more work, but it's less expensive than the automated drives. Moreover, a manual sky guider can be used on altazimuth mounts including those for Dobsonians. The price falls between the $500 and $600 range. Not a "must-have" necessarily; maybe a "could-have."

For the beginner, I recommend three must-have filters: a solar, a lunar and a light-pollution filter.

The only kind of solar filter you should ever use is the reflective type, made of either Mylar or coated glass, which fits snuggly over the aperture of the telescope. These filters allow only a fraction of sunlight to pass through the telescope, making it entirely safe to observe sunspots, convective cells and bright filaments along the solar limb.

Depending on aperture and type of material used, solar filters cost between $30 and $150. Also, be advised that Mylar filters render the sun in a light-blue color, while glass filters (more expensive) render the sun in its natural yellow-orange hue.

If you like to look at the moon, a lunar filter is a must. In almost any size telescope, the moon is so bright, particularly when its phase is greater than first quarter, that it dazzles the eye into "lunar-blindness." Fortunately, like being snow-blind, it's only temporary, but you can avoid this photophobic experience altogether with a simple, low-cost (less than $20) filter that screws on to the eyepiece.

Finally, if you want to observe deep-sky objects and you live in or near a city or metropolitan area you must have a light-pollution filter. LPFs block the kind of light that masks the sky -- specifically that produced by evil mercury-vapor and high-pressure-sodium street lights, as well as naturally occurring ionized oxygen sky glow -- while passing the desirable light from nebulae or galaxies.

These filters often produce amazing results. Deep-sky objects that you think you wouldn't be able to see pop out in high contrast and in detail. Not surprisingly, there are many types of LPFs, some specifically for nebulae, others for galaxies, and still others for comets. Prices range from $60 to more than $150.

In some respects, choosing eyepieces for your telescope is a moot point, since most instruments come equipped with two token eyepieces anyway, but these are sometimes marginal in quality.

Like the lens or mirror of a telescope, eyepieces are categorized by focal length, which is given in millimeters (mm). The longer the focal length, the lower the magnification. So, for any given telescope, a 32mm eyepiece will provide a greater field of view and thus a lower magnification than a 25mm. (To derive magnification, simply divide the telescope's focal length by that of the eyepiece. For example, a 25mm eyepiece used on an instrument with a 900mm focal length produces a magnification of 36x.)

Eyepieces also come in three barrel sizes: 0.965-inch, 1.25-inch and 2-inch. The 0.965-inch (2.45 centimeter) eyepieces are usually supplied with low-cost import telescopes. The quality and selection for most of these eyepieces are poor and the only reason for keeping them around is because they make cheap telescopes even cheaper. Don't buy a telescope with eyepieces of this size.

The 1.25-inch (3.175-centimeter) eyepiece is the most common and is considered the American standard. But gaining in popularity today is the 2-inch (5.08-centimeter) eyepiece, which has been embraced by advanced amateur astronomers who desire crisp wide-field views with their large light-bucket telescopes.

There are countless variations on eyepiece design, with price ranges to match. If you're just starting out, don't buy the most expensive eyepiece, but don't buy the least expensive either. I recommend Plössl eyepieces because they provide sharp, high-contrast images and are good all-around eyepieces for everything from planets to galaxies. A step up in quality, and a significant step up in price, are the Nagler eyepieces, which provide pinpoint star images across a breathtakingly wide field of view. (When the time comes to buy one of these, I suggest the 9mm.)

The following list is purely arbitrary and in no particular order. Although they are not "must-haves," they are useful options that you may want to consider.

• A barlow lens, which will double or triple the magnification of any given eyepiece
• Dew shields for Schmitt-Cassegrain telescopes
• A lens-cleaning brush
• A modest eyepiece case

My final piece of advice may be taken with the proverbial grain of salt, but here it is: If you've reviewed your choices and are still stymied as to which telescope to buy, I suggest being less analytical and more instinctive.

Recreational astronomy should be fun, and fun is something you can't quantify. So, after all is said and done ask yourself -- which telescope do you think you'd enjoy using the most; which telescope has the most potential for gratifying your interest; which one gives you that little tingle of inexpressible excitement?

Go with that one.