Mountings for astronomical telescopes fall into two classes. The first is the altazimuth (abbreviation ALT-AZ), with movement in altitude and azimuth (or, in common language, movement in the vertical and horizontal planes), and the second is the equatorial type, with movement in Right Ascension and declination.

For observing the altazimuth mounting is very satisfactory, but when one comes to astrophotography of celestial objects, the GEM is a better option for longer exposures.

The German Type or GEM, which is most common of the equatorial type mounts, has the telescope on one side of the mounting polar axis and counterbalanced by a weight on the other side, on an extension of the declination axis. One disadvantage of this type is the fact that it is necessary to reverse the instrument when the object passes the meridian.

Normally the telescope is used above the counterbalance weight so that it clears any obstruction by the mounting itself, and is thus easier to use than when the telescope is below the counterbalance weight. On the other hand, the German type is very suitable for the medium-sized refractor and is a compact arrangement.