Which telescope mount is best? There are three common telescope mounts: alt-azimuth, equatorial fork, and German equatorial. And then there’s the mount you find with Dobsonian telescopes. In the following, you’ll find these telescope mounts explained, with diagrams, along with how-tos on their use.
Who is this for? Anyone looking to buy a telescope or has already bought one and wants to get the best from it by knowing how to use a telescope properly starting with understanding how the mount performs.
Why is this important to know? Understanding how the different telescope mounts perform will help you in choosing the best one for you if you’re in the market for a new telescope or mount.
In using your telescope, by knowing more about the mount, you’ll get a better experience. You’ll know what to expect. It will also reduce the likelihood of damaging your equipment through improper use.
What is a telescope mount?
A telescope mount supports the telescope so that you don’t need to hold it.
When talking about a telescope mount, we generally refer to the mount and tripod combined. But, not all mounts include a tripod, e.g., the Dobsonian.
You need a mount and tripod to keep the telescope steady, which is difficult to do by simply holding it yourself.
The mount has moving parts so that you can point the telescope at the stars or other objects and adjust it as these objects move.
It allows you to free your hands for focusing, swapping eyepieces, taking notes, checking star charts, and other activities.
Main telescope mounts explained
Here I compare alt-azimuth, equatorial fork, and German equatorial mounts. This includes the Dobsonian rocker box mount. These mounts all have two perpendicular axes of rotation, though not exactly the same.
If you intend on doing astrophotography, steer away from an alt-azimuth mount. Equatorials are best for astro-imaging. I talk about this further down.
Alt-azimuth mounts explained
In an alt-azimuth (Alt-az) mount, the axes of rotation involve a horizontal axis and a vertical axis. Basically, up and down (altitude), and east and west (azimuth). You can imagine how this becomes trickier as you try to observe an object up toward the zenith where you can’t do a simple up-down-east-west movement.
Alt-azimuth mounts are simple to use and generally cheaper than the equatorial types. This is the advantage and you find these mounts in kids’ telescopes and beginner telescopes that are economical buys.
The disadvantage with these types of mounts is that it’s not that easy to follow the celestial object in the sky a the Earth rotates. A manual alt-azimuth mount requires different rates of rotation of both axes.
There are two main variations in these mounts. One is a ball and socket and the other is a rocker box.
Dobsonian mount explained
Dobsonian reflector telescopes have the rocker box type of alt-azimuth mounts. These are generally lighter in weight than equatorials and the time to set up a Dobsonian mount is minimal. Our review of Dobsonians covers more about these types of telescopes.
What does equatorial mount mean?
It’s a type of mount, as explained by Wikipedia, “that compensates for Earth’s rotational axis parallel to the Earth’s axis of rotation”.
How does an equatorial mount work?
An equatorial mount actually has four planes of movement, latitude, azimuth, right ascension (RA) axis, and declination (Dec).
So the telescope will spin from left to right (azimuth) and move up and down (latitude) on pivot points at the base of the mount (just above the tripod). The latitude axis will be locked, once you set it to your local latitude and the azimuth axis once it is set towards the celestial pole.
At the top of the mount (nearer the telescope) are two axes, based on the celestial coordinate system, east-west and north-south. These are the two directions in which you will scout the sky with an equatorial mount.
The axis that pivots closest to the telescope is the declination (north-south) axis (see image). Once an object of interest is found, you can lock onto and follow it, using only the polar axis. This is the right ascension axis (east-west) which runs parallel with the Earth’s rotational axis when set up correctly.
Equatorial (EQ) mounts are more mechanically complex than the alt-azimuth types. The beauty of an equatorial mount is that by rotating a single axis at a constant rate, you can follow the celestial object as it appears to move with the rotation of the Earth.
Equatorial fork mount
The forked equatorial mount involves a two-pronged fork sitting on a wedge. The wedge or base is aligned with the Earth’s pole and is one axis of rotation and the prongs are the other.
This type of mount is seen in the short-tubed Schmidt-Cassegrain telescopes (SCT’s).
German equatorial mount explained
The best way to describe a German equatorial mount (GEM) is to think of the letter “T”, where the stem of the “T” is the axis that is aligned with the Earth’s pole and the top of the T is the declination axis.
Mounting a telescope
Large equatorial mounts can be heavy. You will have to disassemble the mounting for transportation and reassemble it at the location you intend observing the night sky.
Once you have the tripod set up evenly, add the mount to the top of the tripod by placing the protruding base of the mount into the indentation at the top of the tripod. Usually, there is a knob under the tripod head to secure the mount in place. Tip: Take care not to overtighten.
Put the latitude adjustment screw in place by threading it into the hole at the back of the mount close to the tripod head. Screw it in enough to hold it in place only as you will need to adjust this when setting the local latitude.
Why you need an equatorial mount for astrophotography
Equatorial mounts are better at tracking a sky object you want to shoot. Although it doesn’t seem like it, the Earth is rotating. At the same time as you are trying to capture good astro-images, you are moving relative to that point in the sky. The rate of movement is roughly 1,000 miles per hour (at the equator), according to an article in Scientific America.
Because the celestial body is so far away this movement is not obvious to you. However, it can affect your shots. You may see motion blurs or trails.
With an equatorial mount, you only need adjustment on one axis, the right ascension (RA) axis, once you’ve locked onto an object to follow it. In a manual mount, this requires turning the RA control only.
With an alt-azimuth, to track an object, you need to move the scope both horizontally and vertically and you’ll find the eyepiece field of view will rotate. This is not ideal for astrophotography.
How do you use an equatorial telescope mount?
The main axes are the east-west (RA) and north-south (Dec). You lock the latitude axis with your local latitude and the azimuth is set in place pointing to the celestial pole (directions below). From there, you use the RA and Dec to do your observing.
For the EQ mount to track celestial bodies across the sky it needs to be polar aligned. This means that the RA axis runs parallel to the Earth’s axis of rotation. You need to do this not only for tracking objects across the sky (at high magnifications, especially) but also if intending to do astrophotography.
There are slow-motion control knobs for axes of RA and Dec. To move the telescope some distance across the sky, it is best to loosen the RA and Dec clutch knobs on the side of the mount and move the scope by hand. Once you have it in the desired position, tighten the clutch knobs again.
How to polar align an equatorial mount
Basically it amounts to setting the latitude on the mount to your current latitude (where you are using your telescope) and then rotating the mount on its azimuth axis so that it points true north (vs magnetic north). If you are in the northern hemisphere, find the star Polaris and line up the RA axis with it. It needs to be more accurate if you intend on doing astrophotography.
This video explains how to polar align a German equatorial mount in the northern hemisphere with the help of the Polar Finder app …
How to polar align an equatorial mount in the southern hemisphere
In the southern hemisphere, in places such as Australia that offer some magnificent stargazing locations, you need to point true south.
Here, you need to align the RA axis to the southern celestial pole (SCP). This is slightly more challenging in the southern hemisphere because there is no single bright star such as Polaris that is associated with the southern celestial pole.
The few ways used by amateur astronomers in the southern hemisphere to align the RA axis include laser alignment, known star alignment, drift alignment, and the Crux.
This means you use a laser to align your scope. In regards to laser alignment, local regulations can apply to the use of lasers and, in many cases, they may be banned or you need to register their use.
Known star alignment
The known star approach is for computerized mounts AKA GoTos.
The drift alignment starts by focusing on a bright star that is low on the horizon. If the star drifts north, your RA axis is too low, if it drifts south, it’s too high. The next step is to focus on a bright star on the Meridian (right about your head). If that star drifts north, then rotate your mount clockwise (west) to adjust. If it drifts south then rotate your mount anticlockwise (east) to adjust. Repeat steps until you get it accurate.
Using the Southern Cross (Crux) and pointer stars
With the latitude locked into the local latitude and the telescope set towards the south celestial pole (SCP) on the azimuth axis, the Dec axis is set to 90º and clasped in place. The telescope needs to be sitting strictly over the tripod. To achieve this, it is moved on the RA axis until in position and then clasped in place. It is now in the general direction of the SCP.
Depending on the time of year and the night, the Southern Cross (AKA Crux) is a well-known marker to determine south. Draw a horizontal line between the bright star adjacent to it, Hadar, and Achernar to the west. At the center of this line, where the Crux points to, is roughly the SCP.
Use the finder scope to point the telescope to this area (without moving the Dec axis). Once aligned with the SCP, tighten the azimuth and latitude axes and continue using the telescope based on the celestial coordinate system, east-west (RA) and north-south (Dec).
These notes are taken from this video, which gives a great visual coverage on how to polar align an equatorial mount in the southern hemisphere using the Crux.
What is a GoTo mount?
A GoTo mount is computerized. It will automatically go to a selected object you wish to observe or track. These mounts are more expensive than the manual types and are covered in detail elsewhere. You can find more about these in my guide to the best telescopes for planet viewing.
Understanding how telescope mounts work and what they are best for are things you should know when looking to buy a telescope. If you are wanting to track planets across the sky or to photography them, then knowing you need to invest in an EQ mount rather than an altazimuth, including the Dobsonians, is important.
Telescope mounts explained in terms of how they operate and perform is something to take in to get the most enjoyment out of using your telescope and to avoid harming it through improper use.