There are two main kinds of telescope mounts, alt-azimuth and equatorial. Most books on astronomy recommend the equatorial mount, which is aligned with the Earth’s axis of rotation so that a simple motor on that axis will move the telescope in one direction while the Earth turns in the other direction, the end result being that the telescope’s aim remains fixed in space, pointing at a distant object. This is essential for long-exposure imaging but it’s also desirable for many kinds of visual observation.
Despite all the advantages of the equatorial mount, the simpler alt-azimuth design retains a devoted following. It is simple to use, basically “point and shoot,” and, because it requires no counterweights, relatively light in weight for the telescope it carries.
The very popular Dobsonian telescope uses a simple version of the alt-azimuth mount. Its main disadvantage is that tracking an object across the sky always requires simultaneous motions in two different directions.
With a badly designed mount, this can be a nightmare, but with careful design the observer no longer has to think about it, and tracking objects soon becomes second nature.
Most of today’s Dobsonian mounts do this with ease, but alt-azimuth mounts for other telescope designs often don’t work as well.
The commonest inexpensive alt-azimuth mount today is the AZ-3. This works very well for terrestrial viewing, but causes problems when used for astronomy. The mount is poorly balanced as it points higher in the sky, and the altitude tension is usually set very high to compensate. As a result, it’s very hard to point at anything high in the sky.
Recently Orion® introduced an improved alt-azimuth mount, called the VersaGo. This consists of a standard tripod, similar to that used on many telescope mounts, and a newly designed head which attaches to the tripod. This head consists of four nicely-machined aluminum parts which bolt together with supplied hardware to make a very substantial and solid mount. Both axes have large Teflon bearings and clutch knobs, so the action of the mount is very smooth and well controlled.
The upper plate, where the telescope attaches, uses a standard Vixen cradle as used on other Orion® mounts and those of other manufacturers, so that telescopes are easily interchangeable. The telescope dovetail is held securely in place by two large bolts. The altitude axis is offset, so that the telescope tube can be pointed at the zenith (not always possible in other designs). This also means that the telescope remains balanced no matter what altitude it points at. Finally, there is a long rubber tipped handle attached to the cradle which enables fine movements of the telescope.
Orion® sells the VersaGo mount on its own, or paired with a variety of popular telescopes of different designs: 80mm f/5 refractor, 90mm f/10 refractor, 102mm f/13 Maksutov-Cassegrain, and 130mm f/5 Newtonian.
Since I currently own none of these scopes, I tested the VersaGo with my Orion® 100mm ED refractor, which is comparable in many ways. Mounting was easy, thanks to the standard dove-tail system. I balanced the scope with my favorite 22mm Nagler eyepiece (41x, 2 degree true field of view). This made a perfect system for sweeping the grand vistas of the summer Milky Way, unencumbered by the complications of an equatorial mount. Although it’s easy to rebalance the scope for high power eyepieces by sliding the dove-tail fore and aft, I preferred to use a Tele Vue Equalizer: a solid bronze 2”-1.25” adapter which adds 12 ounces of weight to the eyepiece. A quick twist of the altitude clutch holds the tube in place while changing eyepieces, an advantage over clutchless alt-azimuth mounts.
The one problem I noticed was some vibration at high magnifications. I traced this to the tripod’s stamped aluminum legs. Aside from this, I found this to be an excellent product, clearly superior to Orion®’s older alt-azimuth mounts in every way. Even a scope as large as the 100 mm ED becomes a comfortable “grab and go” on this mount, easy to carry outside with one hand, and extremely smooth and solid in operation.
Geoff has been a life-long telescope addict, and is active in many areas of visual observation; he is a moderator of the Yahoo "Talking Telescopes" group.