Telescope Mounts

The best telescope in the world is useless unless it's on a solid, stable, smoothly-working mount, one that permits it to be directed to the desired part of the sky and to follow a celestial object smoothly and precisely as the Earth turns beneath it.

In realistic terms, a "stable" mount is one that, when you're using a moderate to high power, will not vibrate for more than a second or so after you rap the tube. In particular, the view can't wiggle so much when you hold the focus knob that you can't see when you've found the sharpest focus. And when you let go, the aim must not jump to one side. This completely eliminates the typical "department-store" semi-toy telescope from consideration.

While there are variations on a theme, you'll encounter two types of mount: altitude-azimuth (or "alt-az") and equatorial.

An alt-az mount operates like a tripod's pan-and-tilt head, moving the scope up-down (in altitude) and left-right (in azimuth). Equatorial mounts also possess two axes, but they're tilted so that one can be aligned with the rotational axis of the Earth.

If you're intending to use a small telescope for casual sky viewing or daytime use (say, birdwatching), you'll find the alt-az mount preferable. Well engineered mounts of this type will have finely threaded slow-motion controls that enable the scope to be moved smoothly by tiny amounts, especially important when you're using high powers. The value of such refinements will be all too apparent when you are tracking a star or planet at high magnification.

The Dobsonian is a form of alt-az mount. Inexpensive materials such as particleboard and Teflon figure in its construction, resulting in a low-cost, low-center-of-gravity mount that (ideally) glides smoothly about both axes with fingertip control. A Newtonian reflector mounted in this fashion is not only extremely easy to set up and intuitive to use, but very good value, too.

For a telescope intended for astronomy, and for which photography is a future prospect, consideration should be given to some form of equatorial mount that automatically counteracts Earth's rotation. It's far easier to track a celestial object with a scope mounted this way, since you need only concern yourself with turning the scope about one axis — not two simultaneously, as in the alt-az. When an equatorial mount is properly set up, turning the slow-motion control of its polar axis is all that's required to keep an object in view.

More sophisticated mounts, including modern high-tech alt-az mounts, have built-in electric motor drives to do this, freeing you to concentrate on observing.

So is one type of mount better than the other? Not really, since each has its strengths. For the casual observer who wants a highly portable scope that can be quickly set up in a variety of locations, an alt-az is preferable — especially a Dobsonian. An equatorial, while virtually mandatory for most forms of astrophotography and critical observations of the Moon and planets at high power, needs to have its polar axis aligned with the rotational axis of the Earth. While polar alignment is not particularly difficult and becomes routine with practice, it can take a little time at the start of your observing session if you want to do it really precisely (necessary for photography but not for just looking).

"Go To" Scopes

Currently in vogue are the computer-controlled robo-scopes appearing on the market in various guises. These have mounts that are controlled either by a built-in computer or remotely by an external PC. This allows you to direct the scope to any object in the computer's database.

At first glance these "Go To" units would appear to be the answer to a novice's dream, since they ostensibly take the hard work out of finding elusive objects like faint galaxies, star clusters, and asteroids. "Hey," you might think, "I don't have to learn the sky!"

But it's not quite like that.

There's no denying that when well engineered (read expensive), these robotic scopes are great fun to use, as they almost magically slew across the sky in search of whatever you've keyed in, zeroing in on the target to be presented in the eyepiece. But this technology is only beginning to mature to the point where these scopes will automatically orient themselves when you take them outside and switch them on. Almost all Go To systems will ask you to enter the geographical location of your viewing site (or the nearest city) and the date and time at the beginning of each observing session. This lets the onboard computer calculate the positions of any celestial objects you may care to look at. Often you'll also have to level the telescope's tube, point it north (or south in the Southern Hemisphere), and then launch into an alignment procedure that uses two bright stars (which you must know by name) to synchronize the telescope's coordinate system with that of the sky.

It's true that this setup routine is easily mastered with practice. But it does take time. And for someone completely unfamiliar with the sky, the vast majority of the current batch of robotic scopes have the potential to be very frustrating at first. Still, some help is on the way. The newest crop of Go To scopes include their own Global Positioning System devices to at least tell you (and the telescope) exactly where you are and what time it is, making setup a little easier.

Then there's the question of how accurately the mechanical parts actually point the telescope where the electronics think it's pointing. At astronomical magnifications, there is no room here for even very tiny errors — meaning any costcutting in the mechanical design and manufacturing. A cheaply made Go To scope won't work, no matter how fancy the electronics are.

Here's one last thing to keep in mind: the money spent on a Go To scope's electronic mount could be invested in a traditionally mounted scope of larger aperture.

(Continued on next page)