Besides choosing what telescope to purchase, choosing the right telescope mount to go with it is probably at least as important as the telescope itself.  Additionally, telescope mounts are most likely the most expensive component of your setups. So choosing the right telescope mount is important, as you do not want to get it wrong.

But unlike choosing a telescope, choosing a mount is really easy. There are basically 2 different types of mounts:

• Alt-Azimuth Mounts
• Equatorial Mounts

These mount types differentiate themselves by the axes around which they can turn.  Both types can be motorized and computerized in order to follow objects during long-exposure photographs or just to make the life of the astronomer easier.

Alt-Azimuth telescope mounts

Alt-Azimuth mounts turn around 2 perpendicular axes.  They allow a telescope to turn around a vertical axis, varying the azimuth, and a horizontal axis, varying the altitude.  These are the classical mounts, on a tripod, used by photographers and astronomers.  Their design is simple and they are cheap.  They make excellent beginner mounts.

A special version of these mounts is the Dobsonian telescopes.  These are reflector telescopes on an integrated alt-azimuth mount.  They are meant to be installed on a table or on the ground.  The design allows for much larger mirrors than any telescope on a tripod.

But unfortunately, they are incapable to taking long-exposure images. Neither of their axes allows them to follows the Earth’s rotation. That is where equatorial mounts come in.

Equatorial telescope mounts

Equatorial Mounts turn around different axes.  The first axis is aligned according to the Earth’s polar axis.  The second axis is perpendicular to the polar axis.  Once the mount is aligned to the polar axis, equatorial mounts allow telescopes to turn with the stars around the north or south celestial pole.  This does add some complexity to the telescope setup though, as an equatorial mount needs to be aligned to the Earth’s polar axis before it can be used.

So why go for a more complex equatorial mount over an easier alt-azimuth mount? When taking long-exposure photographs, stars move in the night sky.  Well … the earth rotates against an apparent static celestial background. Anyway, they appear to move, and they move more than you expect.  If you take images with an exposure over 25 seconds, stars will show up in the final image as arced lines around one of the celestial poles.  Equatorial mounts allow you to turn the telescope during the exposure with the stars around the celestial poles in order to generate.

Manually rotating the telescope is a very error-prone process, but that is what motorized equatorial mounts are for. Motors in such mounts can be enabled to turn the telescope against the Earth’s rotation, keeping the telescope always pointed toward the same target.

One last thing about equatorial mounts, the way they are built requires them to have counterweights to balance their telescope. An inconvenience that alt-azimuth mounts not have.

Loading Weight

An important detail sometimes overlooked is loading weight. Each mount will have a specification about how much weight it can carry.  Overloading the mount can harm it.  This is especially important on motorized mounts.  So when choosing a telescope mount, you need to make sure the indicated max can easily carry the telescope and other components (camera, guide scope, …) you plan to add on the telescope.

Be especially careful when buying a telescope that is sold with a mount. In order to reduce the total price, it is not uncommon that such telescopes are combined with a mount that is barely capable of supporting the telescope. The moment you add cameras and other equipment, you easily overload them and you only realize you have the wrong mount when it is too late.

Choosing a mount

So choosing a mount is easy. You only need to know 2 things:

• Do you want to image deep space objects such as nebulae and galaxies? Then you need an equatorial mount, otherwise, choose an alt-azimuth or a Dobsonian mount that goes best with your telescope.
• You need to figure out how much weight think your mount needs to be able to carry comfortably

Ooh yeah, as I stated in the initial post to the ‘ Understanding and choosing equipment’ series, do not be surprised to see the mount show up as the most expensive part of the equipment 🙂