German equatorial mounts

So far we have been considering only fork mounts. German equatorial mounts (GEMs, Figure 4.15) - the kind with the counterweight - can also be computerized. This type of mount should perhaps be called "Estonian" because it was first used on the 9.5-inch (24-cm) refractor in Tartu (Dorpat), Estonia, completed in 1826 - but its inventor was a German, Joseph Fraunhofer.

High-quality computerized German mounts are made by Vixen, Losmandy, Software Bisque (Paramount, shown in Figure 4.16), and Astro-Physics. Unlike forks, German mounts can be sold separately from the telescope because the

Latitude of New York -No problem

(latitude adjustment)

Figure 4.15. "German" equatorial mounts overcome the limitations of a fork.

(latitude adjustment)

Figure 4.15. "German" equatorial mounts overcome the limitations of a fork.

Figure 4.16. The Paramount, an observatory-quality computerized German equatorial mount made by Software Bisque.

Tube east of pedestal for viewing western sky

Tube west of pedestal for viewing eastern sky

wrong way

Tube hits pedesta -. when moved .

wrong way

Tube hits pedesta -. when moved .

Figure 4.17. Two ways to point a German-mounted telescope straight up. To roll over easily from one position to the other, point the telescope at Polaris.

same mount can be used with telescopes of different sizes. Some amateurs have one excellent mount and several telescopes that can be attached to it.

Setting up a GEM can be easier than polar-aligning a fork mount because the mount is easier to adjust and the finder is never hidden between or under the fork arms. The polar axis is an axle, and you can easily see which way it points; some GEMs even have built-in alignment scopes for sighting Polaris. Ordinarily, though, polar alignment is done by pointing the telescope parallel to its polar axis, then adjusting the mount to point the telescope at the pole.

The GEM has one quirk that can puzzle anyone who hasn't thought it out beforehand. As Figure 4.17 shows, there are two ways to aim the telescope high in the sky, depending on whether you want to have room to swing east or west. To "roll over" easily from one position to the other, aim the telescope directly toward or away from the pole.

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