I was asked to give recommendations on what sort of astrophotography setup one could put together with a $3000 budget. The salient facts for this individual are:
1. They already have a DSLR they can use
2. They want to focus on deep space astrophotography
And as of now, that’s all we know.
So this is an exercise in 3 parts, and I’ll walk you through them.
Part 1 – The Basics
Deep space astrophotography in its simplest. most basic form, is comprised of three key components:
- An equatorial mount
- A telescope (or lens)
- A camera
An equatorial mount is one that rotates at the same speed as the Earth rotates on its axis. but in the opposite direction, to counteract the rotation of the planet. These mounts typically have a long bar with a counterweight on them, so that the mount can more easily and accurately rotate around the the celestial pole.
There are a few things to look for or at least to remember when considering mounts for astrophotography. The main one is payload capacity – the mount has to be capable of holding the weight of your telescope and camera and rotate and track the target with control and accuracy.
Most mounts are advertised for their visual payload capacity – that is, how heavy a telescope & accessories it can support for people who are looking through the telescope and doing visual observation. The human brain is remarkably good at compensating for variations in something we are looking at – when we’re looking through the eyepiece, typically a little jiggle in the scope isn’t going to bother us one bit. Cameras however are much less forgiving, as one jiggle in the scope will ruin your whole exposure, which may be 5 minutes long or even more! So a good rule of thumb is when planning for astrophotography, don’t exceed 2/3 of the advertised payload capacity. The AVX pictured here is advertised with a 30 pound – or 13.5kg – capacity, so for astrophotographic purposes we wouldn’t want to exceed 9kgs of payload.
When you’re working to a budget, it is tempting to look for savings wherever you can. But remember that if you skimp on your mount, it doesn’t matter how great your telescope is or how fancy your camera is if the mount cannot hold it steady and track your target.
Next you want a telescope – well really, you want an optic device that captures photons and concentrates them onto a plane so that we can observe or photograph them. Now there are exceptions to every rule, but as a general guide, deep space objects are usually large (so you don’t need huge magnification), and they are usually faint (so you need to capture lots of light quickly). So for this exercise we are going to look at widefield telescopes that have a focal length below about 700mm, and we are going to aim to get f/6 or faster.
There are lots of different types of telescopes – LOTS! – and they all have their strengths and weaknesses, their niche where they excel and then those areas where they are not so strong.
For myself, refractors are generally my first option. For their focal length they are compact, they are generally fairly light and easy to set up and take down, they don’t need regular collimation, and they are familiar – just like an overgrown camera lens really. There are other options available, and many people far wiser than I would recommend you start off with a Newtonian. They may be right, but that is not my advice. Newtonians are large, cumbersome scopes to move around, to set up and tear down; they have a large surface area which makes them – compared to a refractor – more susceptible to being affected by any gusts of wind; and they can at times require fiddling around with collimation (that is, making sure that all the optical elements in the telescope are correctly lined up so that the telescope can focus the light correctly.
Lastly, you need a camera. In this instance our astrophotographer already has access to a Canon 1100D digital SLR, so rather than spend time and money on a different camera when we already have one that will work, we are building this astrophotography rig around the canon. What they will need however is some way to get the camera to continue taking photographs one after the other. In our simplest bare bones astrophotography rig, we accomplish this with an intervalometer. Many Nikon DSLRs have one of these built into the camera, but most Canons – at least all those I’ve used – do not, so one needs to buy a remote trigger or programmable intervalometer to instruct the camera to keep taking pictures. You also need the correct adapter to be able to attach your camera to the telescope – we will talk more about T Rings and adapters in a little while.
So now we have an equatorial mount, a widefield and relatively fast telescope, and a camera that can take photos through it all night long… why isn’t this the end of the article? Because there are challenges that arise when you’re working with this basic setup, and addressing those challenges typically means buying more bits. And if you’re operating on a fixed budget then you need to know what these problems – and solutions – are before you blow your entire budget on a mount and a scope.
Part 2 – The Challenges
There are three main problems that we face when trying to work with the basic setup.
- Bad or unreliable tracking
- Fixed & repeating noise patterns
- Dew
A fourth challenge which many new astrophotographers face – especially in the southern hemisphere – is polar alignment. Getting a good polar alignment is essential for successful astrophotography. It’s a whole topic in its own right so I won’t try to address it here, but as we work to solve these 3 challenges we have an opportunity to make polar alignment easier also, as you will soon see.
To address bad tracking – and assuming that we have already perfected our basic setup as much as we can by properly balancing our payload, tuning out any backlash etc – we introduce guiding. Guiding involves a second (usually smaller) telescope known as a guide scope, a second camera (creatively known as a guide camera), and some software that can talk to the mount. The software identifies a star – or some stars – that are visible to it when the main scope is pointing at it’s target. Then the guiding software measures whether those stars have drifted from where they were a moment ago, and if the have, it issues an instruction to the mount to compensate – that is, it sends a correction to the mount to nudge it back to where it needs to be for the guide stars to be staying put. Guiding can be an art, science, and religion all of its own, but for our purposes it is fairly straight forward. A guide camera looks through the guide scope, and the guiding software keeps “nudging” the mount back on target to correct any drift. Good guiding gives you good tracking, and good tracking gives you nice round stars in your exposures.
Guiding also gives you an opportunity to solve another problem – that of fixed noise patterns.
Notice how the image seems to be streaky from bottom left to top right – this is the repeating pattern of noise. As the target has gradually drifted over the course of the night – fundamentally because of a pretty poor polar alignment (more on that later), bad or noisy pixels from the camera sensor leave their mark in image after image… but as the target has drifted slightly to a different part of the sensor, those noise marks appear to move across the target, resulting in this streaky pattern. The integration has trouble identifying it as noise because it is so similar one picture to the next (that is, it lacks randomness) so mathematically it looks like part of the signal, not random noise.
Good calibration files will help reduce or eliminate this too, but what makes a big difference is dithering. When we dither, our guiding software moves where the camera is pointing between exposures – eg it moves randomly 20 pixels up or down. And as soon as the noise from those pixels appears random, then the integration routine has a much better chance of eliminating it. Dithering is good for a couple of other reasons too, but fundamentally it helps keep your pictures clean, by making a clear separation between what is signal (that is, the light that was emitted from your target that you are trying to capture) and what is noise.
The last issue we’re going to solve is dew forming on the front lens of our telescope. Most telescopes will have a dew shield but the most effective solution is to put a source of heat on the element so that it remains above the dew point temperature.
These little dew straps are not particularly expensive. Of course as with all things in astrophotography, you can find a more expensive variant of any part that you could think of! For now, we’re operating on a budget, so we are going to stick with the eBay heater which is all that we need.
Part 3 – The Solutions For The Solutions
We started with something very simple and basic – one mount, one telescope, one camera. But as we moved through addressing some of the challenges, you will have noticed new items being discussed, such as a guide camera, a dew heater, or “software”. For our ultra basic rig, all you really need is power for the mount – you can charge the battery on your DSLR and even buy a spare or two, and then so long as you can power the mount, you’re good to go. No longer – we have software, and we have heaters, and we need to control all this somehow.
First up, how do we use software to control all this? You have 3 choices really:
- Grab an old laptop you have lying around, and give it a new job to do.
- Buy (or build) a computer specifically for the purpose
- Use a Raspberry Pi based solution – basically a mini computer out on the scope, that is controlled from your computer or your phone.
Operating an astrophotography rig isn’t particularly demanding in computing terms, so grabbing your old laptop is probably not as crazy as it might sound. Having a computer out at your telescope – be it new or old – you still need to power it (unless the battery lasts all night!) and you probably need to protect it from dew and other outdoor hassles. There is a very high tech solution available – the plastic storage box. Just make enough of a gap for USB cables go do through and then once you’re up and running, you can close the box and leave the computer to it. Easy.
You can buy computers specifically for driving astrophotography – such as the Prima Luce Lab “Eagle” series. But not in our budget. Ditto building a machine using a NUC – cheaper than the Eagle, but still, not cheap.
The third option is my recommendation here. Though you can get a Raspberry Pi and install astroberry on it, I’m too lazy, and this is for a beginner’s setup. So my recommendation here is an Asiair produced by ZWO. This can be controlled from an app on your phone or tablet, and on the whole is a very easy and effective way to get started in astrophotography. They’ve also been around for a little while now, so you can pick them up second hand, which always helps when working on a budget.
What does our final shopping list look like? Well here it is, using second hand examples from Ice In Space as examples to keep things in budget:
- Mount = Celestron AVX equatorial mount – $1,000 (used)
- Telescope = SkyWatcher EvoStar ED72 with flattener – $800 (used)
- Guide scope = SVBony 50mm Guide Scope – $80 (used)
- Guide camera = ZWO ASI120MM Mini – $270 (new, Astro Anarchy)
- Dew Heater = SVBony 12v Dew Heater 480mm – $35 (new, Amazon)
- Controller = ZWO AsiAir Pro – $350 (used)
- Power = 12V DC 10A Desktop Power for Asiair & Accessories – $90 (new, Jaycar)
2nd Power (for mount) = 12VDC 7.5A Power Supply (to Cigarette Lighter Socket) – $60 (new, Jaycar)
Weatherproof Outdoor Powerboard Enclosure – $35 (new, Jaycar) - T-Ring = 48mm T-Ring For Canon EOS – $40 (new, Astro Anarchy)
- Adapters – Bintel 48-42T Stepdown – $20 (new, Bintel)
Bintel T-Thread Spacer Ring Set 42mm – $60 (new, Bintel)
Bintel 48mm T-Thread Spacer Set – $60 (new, Bintel)
I’ve probably gone a bit overboard with the adapters here, but this comes in at a neat $2,900 – and with our Canon 1100D charged up and ready to go, we are in business. Though since we have a little bit left in our budget, we will lash out and buy a dummy battery for the Canon for an extra $23. Now we can power the camera from our Asiair, and not have to worry about it going flat or changing batteries during the night.
The only thing to add at this point is that the Asiair Pro / Asiair Plus has a really nice little tool to assist with Polar Alignment, even when you can’t see the celestial pole. This is a life saver when you’re starting out – and when you’ve been doing it for years for that matter!