Next page | Contents page |

Camera on an equatorial mount

Motor follows the stars as the Earth rotates about its axis

Then we can use much longer exposures - a minute or more (but still stack)

This is sometimes called a GEM, which stands for German Equatorial Mount.

The beauty of this kind of mount is that once it has been aligned on the pole (more about this soon) it only has to be driven about the one polar axis at a constant rate.

A truly constant rate is hard to achieve. There will be some inaccuracy in the gears unless you pay a huge amount of money. So we can do longer exposures on this mount but only up to a few minutes.

There are other kinds of mounts. The altazimuth mount also has 2 axes at right angles to each other but one is vertical (azimuth) and the other is horizontal (altitude). A computer program can drive the two axes together so that the telescope follows the stars but the field of view slowly rotates. Stars could trail slightly due to this rotation, so this is less suitable for photography.

There are also smaller GEMs designed only to take the weight of a camera. The saving in cost over the type shown is not huge but the one shown is able to take a sizeable telescope. That is why I chose it: I started with camera only but added a telescope later (as we will see).

The mount shown is a basic non-goto version. "Go-to" mounts are intended to be helpful to beginners because they have a large database of objects that can be pointed to automatically. However, they are much more complicated to set up and also I think it is better (more educational, more satisfying) to learn how to find things for oneself. So I am not at all keen on goto mounts (there is further explanation of this on my web site:

Next page | Contents page |