Most astronomers would agree that the mount you use for your astrophotography setup is the most important component. In fact, it could be said that the ultimate quality of your final images is largely related to the telescope mount you are using. It is also usually the most expensive piece of astrophotography equipment that you are likely to buy so your choice is very important.
There are two main types of telescope mounts with tracking suitable for astrophotography, Az-Alt, and Equatorial. The most popular is the equatorial mount as it counteracts the rotation of objects in the sky. Az-alt mounts cannot counteract this rotation without additional expensive equipment.
We will look in more detail at the differences between types of telescope mounts, which should help you to choose the most appropriate type of mount for your needs. Before buying any kind of astrophotography equipment you need to completely understand what it does and how it works and this is particularly important for the telescope mount.
Please note also that a telescope mount can be used either with a telescope or with a camera such as a DSLR with a suitable lens. The important function of the mount is to support your equipment so it does not move easily and to track the movement of the stars and other objects such as planets and deep sky objects (nebulae, clusters, and galaxies) so that we are able to take long exposures of up to many minutes without any star trails or blurry images.
How Does a Telescope Mount Work?
A telescope mount does two things:
It tracks the movement of the stars and other objects in the night sky as they rotate around a point in the sky to the north and south which is an extended line representing the earth’s axis of rotation.
It must carry the weight of your equipment on the mount and balance them as the mount moves the telescope to follow your desired target.
When using a telescope for visual purposes only a mount can be adjusted manually and does not need a tracking motor to follow the movement of the stars. However, in astrophotography, we need to track the stars and follow them accurately so we can take longer exposures of up to several minutes. If we don’t, we will see star trails and get very blurry images.
A mount moves the telescope to point at your astronomy target because it has a motor, but to track the movement of stars it needs to know where it is and where it needs to go. Many telescope mounts have a GOTO system that is programmed with the coordinates of many stars, planets, and deep sky objects but it also needs to be aligned with known stars first so it can find its way around the sky.
A motor is used to move the telescope at a set speed to keep the astronomical object in the center of view of the telescope so that it can be photographed in a fixed position. There are two different systems that telescope mounts use to track the movement of celestial bodies as we shall see in the next section.
Types of Telescope Mounts: Equatorial vs Alt-Azimuth
Two types of telescope mounts solve the problem of the movement of celestial objects such as stars and nebulae. The first is the Alt-az telescope mount and the second is the equatorial mount.
The Alt-az Mount
Once a mount knows where it is pointing it can find and track the movement of stars and objects at any point in the sky by moving in two directions. The first direction or coordinate is altitude – the angle between the horizon and the point in the sky where the target is. The second is azimuth – the direction 0-360 degrees from true North clockwise to the target. For example, due East would be 90 degrees, due South 180 degrees and due West is 270 degrees. Therefore, for this system two motors move the telescope to the correct coordinates on each axis.
Any object’s location in the sky has two coordinates which are both degrees (see diagram below). The point in the diagram is at 45 degrees altitude and 45 degrees azimuth.
An alt-az mount, therefore, can point to and track any point in the sky but it cannot counteract the field rotation because as we are on a globe the stars move in a circular motion around our planet’s axis projected into the sky in the North and South. You need another piece of equipment to do this which is a rotator and this can be expensive. For an explanation of why field rotation is a problem in astrophotography when stacking many photographs taken over a long period of time, we need to look more deeply into the stacking of astrophotos.
An equatorial mount is a cheaper option than an alt-az mount plus a rotator. The reason is that the way an equatorial mount works is that it is inclined to an angle corresponding to the latitude of the location where the telescope is situated and then only one motor is required to move the telescope in what becomes a movement about one axis. If we align the telescope so it is parallel with the earth’s axis of rotation we will solve the field rotation problem.
This alignment is called Polar Alignment and this is easily done in the Northern Hemisphere where we just point the telescope at a point very close to Polaris, (The North Star). In the southern hemisphere, this is not as easy as there is no convenient star above the Southern polar axis.
As the equatorial mount solves the problem of field rotation and can track the movement of the stars etc. most amateur astrophotographers use this type of telescope mount. Last year I switched from an alt-az mount to an equatorial and I am now very happy with the results I get with longer exposures possible and a cleaner result due to the lack of field rotation and the resulting stacking artifacts this caused in my images.
When I used my Celestron 130slt az-alt mount I was able to do 30-60 second exposures maximum and still had to reject about 20-30% at least before stacking them. Slight errors in one of the two motors cause errors in tracking and the images I produced were not as good as the images I can get with my present equatorial mount, (the Ioptron CEM26).
Before I started guiding to increase the accuracy of tracking I immediately saw an improvement in maximum exposure time as the equatorial mount I have can comfortably cope with two-minute exposures with about 10% rejection before stacking.
As mentioned I also get fewer stacking artifacts because the image is in the same orientation almost exactly throughout the night, (although it does reverse when it passes the Zenith or Meridian as the telescope has to flip by 180 degrees).
If you would like some more information on how mounts work and why we need them, with some explanation of some of the reasons why some inaccuracies occur. Take a look at the video below by Cuiv the Lazy Geek:
Factors to Consider When Choosing a Telescope Mount
There are a number of factors to consider when choosing a telescope mount. These include:
How much do you want to spend?
Are you using your telescope for astrophotography or for visual observation?
How much does your equipment (telescope and accessories, guide scope, etc.) weigh?
What objects are you intending to photograph?
Are you going to image from your backyard or will you travel with your equipment?
How much light pollution do you have?
The amount that you spend will directly affect the amount of choice you have and the quality of the mount you can buy. With a more expensive mount, you will get extra accuracy of tracking and a higher capacity of payload so you can use heavier equipment. The quality of your imaging should benefit from spending as much as you can afford on a good-quality telescope mount.
For astrophotography, you need a high-quality mount that will track well and probably have some form of a computerized system to locate and track different objects. This is much more important than if you plan to observe as you can either manually adjust your telescope when observing or tolerate imperfections in the tracking which will probably not be obvious to your eye.
Astrophotography tends to require lots of additional equipment which can make your setup heavy and therefore balance becomes important. In other words, if you plan to do visual astronomy then you can use a simpler setup.
The Weight of Your Equipment
The more accessories you use and the heavier your telescope, guide scope, etc., the more robust your telescope mount needs to be. This may make it less portable and more difficult to set up for a night’s imaging.
What Are You Imaging?
The targets you choose to image and the type of astrophotography you are doing will influence the setup you use. If you want to image the Milky Way for example, you don’t need a telescope at all but you will need a mount that is more portable and can be more lightweight. You will probably use a DSLR camera in this case which does not weigh very much.
If you are imaging planets and solar system objects then you do not need to take long exposures, so the tracker becomes much less important. As long as you can locate the object and roughly follow it you can take photographs through a telescope in much less than one second for each exposure and even take video that will break up into many separate shots of the object which can then be stacked and processed.
As you will not need long exposures and you can tolerate your object moving a little you can use a less accurate mount or simple tripod with your telescope.
Where Will You Image?
You need to consider not only how but where you will usually image your targets because this can influence your choice of telescope mount. If you intend to travel to different locations in search of dark skies, for example, you’ll definitely need a mount and setup that is not too heavy, easy to set up, and portable.
If you have a good location at home or in a fixed place then you might be happy with something more permanent and in this case, you can invest in a heavier and better quality mount. In this situation, you’ll also save time because you won’t have to travel, move equipment or set up before each imaging session. There will be no polar alignment, and your equipment should need just a few quick checks before you can commence your imaging session.
If you do think about a permanent situation then everything can be simplified and fixed. You may consider a telescope pier which is a fixed mount constructed in place and designed not to be moved. These are also very strong and support a lot of weight.
The level of light pollution at your location is important and will influence a number of factors that may affect what kind of mount you should get. Light pollution will limit your exposure and increase the time it takes you to get good results. You will still need a good mount but longer exposures will not be possible so tracking accuracy is not as important.
However, going back to the point above, you may wish to go to a darker location to image and so you will need the possibility of good tracking to take advantage of those locations plus your setup needs to be lighter in weight and more portable.
Top Telescope Mounts for Astrophotography
For now, I’d like to recommend you go with one of the major telescope brands and consider buying one of the models that are well-known by astrophotographers. A lot of the best mounts are discussed in forums such as Cloudy Nights or Stargazer’s Lounge, so go check those discussions out.
I am going to do some detailed research and I will update this page with a selection of the best telescope mounts you can buy. Not just in my opinion but what do those who own them say?
So if you’re reading this please come back and check out my recommendations when I publish them here very soon.
Conclusion: Selecting the Best Telescope Mount for Your Needs
As we have seen, there is a lot to consider before choosing the best mount for your needs. Everybody is different so you need to think carefully before spending the money necessary on a good mount. Finally, I have to say that if you are serious about astrophotography, as I am, you need the best mount you can afford. Good luck and happy imaging!