EQ or Alt-Az mount to start astrophotography?

Why you need a good mount

Updated: Sep 18, 2019

So you are thinking about getting into astrophotography and you’re not sure what to buy first. Where do you start? The first thing that you might think of when getting into this hobby is to buy a more expensive telescope and a dedicated astro camera. Although this indeed improves the quality of your images, there is one far more important piece of equipment that I would recommend to upgrade before buying a new telescope or camera, and that is…your mount. It might not sound very exciting, but in this blog I explain why your mount may well be the most important piece of your equipment when getting into astrophotography. I will discuss why you need to buy an Equatorial Mount rather than an Alt-Az mount, although the latter one is easier to setup and use. Moreover, I will advise you on what criteria you can use when shopping for a new EQ mount. Oh yeah, one other piece of advice; take it slow and be patient. It takes time to master this hobby. I’m three years down the road and I’m still learning.

Why a tracking mount?

So, why is a mount so important? Let’s first start with your eyes. When you look at the nightsky, what do you see? When you are in the city like me, you will see a few dozen starts flickering in the nightsky, and maybe a planet or two. Impressive, but not exactly a Hubble Telescope like picture…So how do amateur astronomers like myself get images such as this?

The ultimate secret is….using a long shutter speed! The above picture you are looking at contains about 180 images, each taken with a shutter speed of 300 seconds, stacked together and processed in Photoshop. If you are interested in the details of this picture, you can click here. Why do we need such crazy long shutter speeds? Just remember the Star Wars opening sentence: “A long time ago in a galaxy far, far away….” This is quite fitting, as you probably know that planets, galaxies, star clusters and nebulae are indeed at great distances – both in space and time – from our home planet. I will get into a small astronomy lecture here, just for fun, If your not interested, feel free to skip this paragraph.

We are nowhere to be found…

You probably know that light travels at about 300.000 km p/second. It travels from the earth to the moon in about 1 second. Rays from our sun – at about 150 million km from earth – take about 500 seconds (8 minutes and 20 seconds) to reach us. So, when you are looking at the last minutes of a sunset, the sun is actually already below the horizon. Light captured from Mars? On average 12 minutes and 30 seconds old. Saturn? About 67 minutes. The closest star? Proxima Centauri. It is about 4.22 light-years from Earth. So we are looking at Proxima Centauri as it was 4 years ago. Hey, that’s when I thought about buying my first telescope. The Orion Nebula? 1,345 light years from earth. Just think about it, light that we receive right now from the Orion Nebula (2019) started it’s long journey to earth in the year 674 AD. So any intelligent life out there in the Orion Nebula looking at our earth with an extraordinarily huge telescope would be able to image the Siege of Constantinople: The Arab fleet enters the Sea of Marmara and appears before the southern walls of Constantinople, in an attempt to blockade the Byzantine capital. Ok, yes, I looked that one up. It gets even more bizarre when looking at other galaxies. Andromeda, our closest neighbour? 2.537.000 light years away. Advanced civilisations over there with an (ahum) astronomically huge telescope would be able to watch the birth of the first oxygen producing organisms on earth – no signs of dinosaurs or humans yet! If they would look in the right direction of course…if I would use my 80MM refractor telescope from any planet in the Andromeda Galaxy, our entire milky way with it’s 200 billion stars would easily fit my field of view. Yes, we are tiny creatures floating around on a pixel of dust nowhere to be found in space nor time – got it. Stop teaching us and get back to astrography. OK, I’ll do, but the above story is why I picked up this hobby in the first place!

Equatorial mounts to the rescue

So, we are capturing very faint light from a long time ago in galaxies, nebulae and star clusters far far away. We need minutes, or even hours, to capture enough of that light on our camera sensors to compose a nice image of an astronomical object. That is tricky, especially when you are on spaceship earth that rotates around it’s own axis every 24 hours . So, the stars – just like the sun – will rotate from in the east to west (when looking south) during the night. When you take a picture with your DSLR camera on a regular (non tracking) mount and set your shutter speed to 1 minute, you will undoubtedly notice what is called star trailing. In the video below, I’ve captured 30 second images of the southern sky above my city during 3 hours with my Canon EOS D1200. Mars and the stars are travelling west. And when stacking those images together, you can see what happens when we would make a picture with a long shutter time, you get star trailing.

So imagine your DSLR behind your telescope with a narrow field of view. You will notice that objects quickly move out of your field of view. A good example would be my bloodmoon timelapse video, where I actually failed to accurately track the moon, resulting in a gittery timelapse video where I needed to compensate manually for the inaccurate tracking (but it was fun to make nonetheless).

Which mount? Alt-AZ or EQ?

So, OK, you need a motorised mount that can track objects in the nightsky. What are your options? You probably already noticed that you can choose between a so called Alt-Az mount or a German Equatorial (EQ) mount. Alt-Az is a celestial coordination system that determines where objects are in the sky, without taking into account your location on earth. An Alt-Az mount tracks the nightsky along two axis, Altitude (ALT) , in which the lowest point on the horizon equals 0 degrees, and the highest point 90 degrees (zenith). And Azimuth (AZ) – which is the 360 degree circle at your location. Alt-Az mounts are easy to use and fairly inexpensive. You can put down your Alt-Az mount anywhere you like and perform a star alignment with two or three objects in the sky, and you are set to go. So what’s the problem? An Alt-Az mount does not take into account your latitude, and does not align your telescope with the celestial pole. Why is that important?

Depending on your latitude on earth, the stars will describe a different path along the sky. Look at this picture and imagine yourself standing on the north pole. The stars and planets would move in azimuth only, from east to west, without any changes in altitude. Now imagine standing on the equator. In that case, stars would move mainly in altitude, not in azimuth. So, an Alt-Az mount can track the stars accurately at the poles and at the equator, when it only needs either the azimuth or the altitude motor. But, unfortunately, most of us do not live at the equator, and certainly not at the north pole. In my case, I’m at 52 degrees latitude in the northern hemisphere. This means that the stars at my location – just like the sun – follow a curved path along the nightsky. An Alt-Az mount can only move vertically or horizontally. Although it is able to track objects, it would move a bit in Az and then in Alt to keep the object in the field of view. It is unable to accurately track the stars along a curved path, which results in star trailing and bloated stars when using long exposure times.

A German Equatorial (EQ) mount can accurately track curved paths. Why? Well, all EQ mounts are aligned with the celestial pole (either south or north), and can be tilted to accommodate the latitude of your location, in my case 52 degrees. It then tracks the stars using it’s DEC (declination) and RA (right ascension) axis. RA and DEC are to the sky what longitude and latitude are to the surface of the Earth. RA corresponds to east/west direction (like longitude), while Dec measures north/south directions, like latitude. I’ve made an animation using stellarium – a free open source planetarium program. In the animation below, you can see that Alt-Az mounts can only accurately track the nightsky at the northpole (a bit chilly there though) or at the equator. If you are at any other location, you need an EQ mount.

OK, so I need an Equatorial Mount, but which one?

My advice would be to look critically at four aspects;

1. How much weight can the mount carry?
2. Does it have an automated tracking option?
3. Can you connect an autoguider to your mount?
4. Is the tracking accurate enough for astrophotography?

Equatorial mounts come in all shapes and sizes. You can already get one for $100! Wow, cheap. I have to warn you though, most cheap equatorial mounts are not accurate enough in their tracking for astrophotography. You will see that once you have checked off the above four questions, you will end up with a mount that may be closer to 1000 euros/dollars, or even higher depending on the telescope you have. I don’t want to disappoint you, but I also want to be honest. Anything below 500 dollars usually brings about a lot of frustration – although there are some grab ‘n go EQ mounts that – when used in combination with a light payload (e.g. only a DSLR camera) might be useful. If you want a mount that can support a light astrophotography telescope such as a small refractor, then mounts start at around $1000. You can check out my video below, where I’ll discuss my Celestron Advanced VX mount as well as some alternative options as good beginner mounts to start your astrophotography hobby.

How much weight can the mount carry?

The first thing you should check is whether the mount is able to carry your telescope + camera. For example, in my case, I have a 3,2 kg Photoline 80mm APO refractor as my telescope. The ZWO ASI 1600MMpro cooled camera which I have reviewed here weighs about 500 grams and I’m also using an Orion 50MM guidescope (700g) with a ZWO ASI 120MC camera (100g) to guide my mount (more on that in another blog). So in total, my mount should be able to carry about 4,5kg (=9,9 pounds). In the list above, I mention (max.) payload in lbs/kg and 70% of that weight. Why? Because in general you do not want to be at maximum payload capacity when doing astrophotography. I have a lightweight setup, so most of the mounts would meet my payload requirement, with the exception of the iOptron SmartEQ Pro and the Vixen Advanced Polaris, which are made for a smallscope and/or camera only astrophotography imaging.

Does the mount have a tracking option?

The second thing to check is whether or not the mount has an automated tracking option. Without automated tracking, it becomes very cumbersome to manually track the mount. Manual adjustments often cause minor vibrations as you attempt to keep the object in the field of view, resulting in blurred images. Today, most mounts have automatic tracking capabilities, but the Celestron Omni (CG-4) in the above list does not. Moreover, most mounts with automated tracking have software that enables you to remote control your mount from your laptop or computer. For example, you can check out the video below, where I show you how I can remote control my Celestron Advanced VX using nexremote software. Nowadays, there are even more advanced options. For example, the latest hardware and software such as the ZWO-ASIair allow you to control your mount remotely via WIFI, without the need of running USB cables to or from your laptop or PC. You only need your smartphone or tablet.

Does the mount support auto-guiding?

A third requirement for astrophotography is the option to auto-guide your mount. Although this is probably not something you will pick up right away, I would advice you to get a mount that supports auto guiding. What is it? Well, in short, auto-guiding involves attaching an additional (small) telescope with a camera to your mount. This second camera can track a star close to your object of interest, and send automatic corrections to your mount to track the guidestar, while your main camera photographs the object of your interest. You want to have this in addition to polar aligning your scope (see above video), as it results in very accurate tracking which enables you to take images with shutter speeds of multiple minutes. In the above list, we can see that four mounts do not have auto guiding capability. This will result in poorer guiding, although it may still be accurate enough when using a small scope or a DSLR camera with a wide field of view. Most people nowadays use software such as PHD2 for autoguiding.

Does my mount track accurately enough to get nice astrophotography images?

This question is not so easy to answer. Besides the requirements discussed before, this also depends on the accuracy with which the mount is able to track. A much discussed topic among amateur astrographers is the amount of periodic error (PE) a mount has. Periodic Error is a small mechanical error in the accuracy of the tracking in a motorised mount that results in small movements of the target that can spoil long-exposure images, even if the mount is perfectly polar-aligned and appears to be tracking perfectly in short tests. The cause of this can be that the the wheel and the worm of the RA and DEC motors are too far apart, resulting in backlash. If you’re interested in this process, please check out my video where I try to solve backlash issues of my Celestron Advanced VX. You can see how the two motors drive the worm which makes your mount move, and how to adjust .

Another thing that can happen is that the wheels and worms themselves are not perfect, resulting in guiding issues. For example, it might be the case that a very tiny piece of the wheel has broken. You will then experience inaccurate guiding, everytime that section of the wheel drives the worm. There is software available that can help train your mount to detect such systematic periodic errors (PEC tool for celestron mounts). I found this (old) spreadsheet on the internet that might be of use to you in determining periodic errors for various mounts. It’s pretty old so don’t take this information for granted.

Another question you should ask is: How wide or small will my field of view be when using my specific telescope and camera to photograph the nightsky? There are various calculators available with which you can determine what your field of view will be with a particular combination of the telescope and camera. In general, when you use a telescope such as me – a small refractor with a low aperture (80mm) and short focal length (480mm; i.e. resulting in a low f-ratio) and a large sensor camera – such as a DSLR – your field of view will be larger, thus the accuracy of your guiding becomes less critical. In contrast, small sensor cameras in combination with large aperture and long focal length telescopes result in a narrower field of view, which increases the need for accurate t.

Is it difficult to use an Equatorial Mount?

As with everything, it needs some practice. As even I could master this job, I’m pretty confident that you will succeed as well. If you want a detailed account, you are welcome to check out the video below where I explain how I setup my Celestron Advanced VX. It was one of my first videos, so please bear with me :-).

Final thoughts

I hope this blog helped you to understand the importance of the mount as part of your astronomy equipment. The most important thing you need to remember is to buy an EQ mount, not an Alt-Az mount. Also, check the maximum payload, take 70%, and check if this figure is sufficient to carry your telescope, camera and any other gear you might have. Also make sure that the mount supports automated tracking and auto guiding. You may not use it right away, but when you do, it will greatly increase the sharpness of your multi-minute images. A final piece of advise is to start out with a small size telescope (refractor or reflector with small aperture and low f-ratio) plus a large sensor camera such as in a DSLR. It will protect you from the frustration that comes with accurate guiding at high levels of magnification. I myself made the choice to start out this way and I don’t regret it. Please send any feedback to me in the comment section below. I’m happy to hear your thoughts.

Clear skies!