Astronomy Camera Buying Guide (with Recommendations!)
Introduction to Astronomy Cameras
Visual astronomy is fascinating. There's nothing like seeing Saturn with your own eyes, or see more and more of the Great Nebula in Orion as your eyes become accustomed to the dark.
And all this is better if you're watching through your own telescope.
But if you're anything like me, you'll start to ask how can you record these views? After all, they're too good not to share, and having photos on your phone will be a serious conversation starter.
And all this is even better if you've taken the photos yourself.
But how? There's a bewildering range of cameras available. What's worse, there's no such thing as one camera that does everything perfectly. Like any tool, cameras are specialised to particular jobs.
Many people start DSLR astrophotography, but many people don't have one and they can be very expensive - much more expensive than a starter astronomical camera. What's more, DSLRs are excellent generalists - that is to say, they're really good at taking mediocre pictures, no matter what target you have in mind. Then there's the people who start with their simple smartphone camera using basic smartphone adapters. This is a very simple and budget option available to almost everyone. Smartphone adapters start from just $44.95. However, if you want more control over your images, you'll want something with more features. This is where astronomy cameras fit in.
Astronomical cameras, or astro imaging cameras are very simple and small devices, little more than just CMOS sensors, which connect to a computer, normally via a USB cable. They can be used for astrophotography or as a streaming tool so you can see your telescope's view on your computer.
Despite its simplicity, there is a huge range of astronomical cameras available. But just to make it confusing for beginners, they all come from different brands and almost always, they are frustratingly and confusingly named in complex code which consists of a series of numbers and with long names. However, in a nutshell, different astronomical cameras are intended for different targets, different exposures and different types of images. There are colour cameras or monochrome cameras; cooled or non-cooled sensors; large or small sensors; large or small pixels; or front- or back-illuminated sensors. So then how do you narrow down the choices to fit your needs? What do they all mean?
How do you choose?
Over the next few sections, I'll try to classify, discuss, sift and recommend types of cameras that would suit astrophotographers who are just starting.
Different astrophotographers have different opinions on this matter. However, these recommendations serve to provide a good set of features and criteria I would recommend to suit specific uses and present the best overall value. There will always be some disagreement, due to the myriad different attributes, functions, advantages and disadvantages these cameras have. And without getting into the technical details, such as quantum efficiency and well depth, it is almost impossible to choose an unambiguous winner.
This is, for a lot of beginners, at least, the most important factor. You've already paid a chunk for your telescope and mount, how do you avoid shelling out heaps more on photographic gear?
Very few people start with an expensive camera as their first one. It's not unknown, but it's rare. So while I might talk about what top end cameras do, I'll confine myself to a budget of around A$1000 (which I'll probably end up stretching for something special), which is what I think would suit a beginner to astrophotography.
So let's start looking at cameras and sorting out what a good first camera will be.
Cooled or non-cooled?
One of the things that beginners notice first about astronomical cameras is that some of them have refrigerators built in. Yes, refrigerators. Lowering the temperature of the sensor decreases the amount of electrical "noise" that gets into the image. This noise shows up as speckles all over your image, and gets worse in longer exposures.
If you're after bright targets like planets or the Moon, your exposures are going to be short - normally less (often much less) than a second. This length exposure won't benefit much from cooling.
But if you're after dark, deep-sky targets, your exposures are going to be into the minutes, and cooling is a good way to reduce the noise. However, it's not the only way. If you take the same photo time and time again, you can use "image stacking" in processing. This is a mathematical process that is quite effective in noise reduction, so while a cooled camera will give you better results, it's not necessary for a good image.
The problem is that a cooled camera is expensive, and above our rough A$1000 budget. Cheapest cooled CMOS is the ZWO ASI183MC Pro or the QHY 183C at around A$1300.
For the purposes of this exercise, I'm going to assume your first camera is a non-cooled model. You're welcome to disagree.
Monochrome or Colour?
You can get cameras that shoot in colour, or cameras that shoot in monochrome. There are big advantages for monochrome, and many advanced users swear by mono imaging.
For a start, resolution of a monochrome image is four times that of a colour image. This is because colour images have to combine (usually) four pixels on the sensor to represent one "colour" pixel. But the other cool thing about monochrome sensors is that you can shoot through filters and get additional types of images, full colour, narrowband, infrared, or other types.
Of course, for a monochrome camera, you're going to have to buy filters and either a filter drawer or a filter wheel. None of this is cheap, and this brings me to the disadvantage of monochrome cameras: expense. My rig runs an ZWO ASI1600MM-Pro with a filter wheel and 31mm colour and narrowband filters. A bundle like this would cost about $3000.
Only compounding things is that for monochrome cameras, the processing is a chunk more difficult. Every time you take a shot, you'll have at least three different sub-images that you will have to align recombine, balance, etc. The learning curve is steep.
To keep things simple, I'm going to assume that you're going to go for a one-shot-colour camera.
What target? Planetary, deep sky, or lunar
We've whittled the range down to uncooled colour cameras. Now, we have to start deciding on your choice of target, because that's going to affect the choice. Are you going to be photographing planets, or deep-sky objects like galaxies and nebulas?
The important difference between these targets is that planets are tiny and bright, and deep-sky objects are dim and large. While there isn't really one "first" camera that does both well, there are a couple that have a go.
What you probably already know, is that you faced the same choice when you got your telescope, so this decision may already have been made. A short focal length (low magnification) telescope, say, under 1000mm, is more suited to deep-sky objects. On the other hand, a Schmidt-Cassegrain with its long focal length and high magnification, is more suited to planets. This isn't, of course, a hard and fast rule. Schmidts are perfectly capable of photographing deep-sky objects - it's just more of a challenge in guiding.
OK, now I've finished telling you why and how I've done this evaluation. So, for planetary, deep-sky and lunar images, here are my thoughts on cameras. I've added a "budget camera" at the bottom as a bonus.
Cameras for planetary work
Remember I said that planets are tiny and bright. They tend to show up in images as a little object surrounded by a sea of black.
That's right, you're wasting all that sensor taking a high-quality photo of black. You'll probably just end up cropping it. Is that a problem? Well, frankly yes, it is.
One of the most useful techniques for photographing planets is "lucky imaging", which takes thousands of images which you sift through later on. If your computer is wasting time downloading millions of black pixels, you're not getting the number of images you need for processing.
What you need is a small sensor that takes a short time to download, so it's getting onto the next image as fast as possible. How small a sensor depends on your telescope's magnification, of course.
But as well as a small sensor, you want to pack as many pixels into that tiny target as you can - so the pixel size should be small. Some people say that the ideal pixel size in microns is one-fifth of your focal ratio, so for example if you have a Schmidt-Cassegrain and a Barlow, your focal ratio is 20, so the ideal pixel size is around 4µm. This is just a recommendation, but it's worth considering.
So what cameras? As always, there's a choice.
My favourite though, is the QHY5-III 462C or the ZWO ASI462MC USB 3.0 Colour Astronomy CMOS Camera. This pair has the 5.6x3.2mm, 2 megapixel (MP) Sony IMX462 sensor. The pixel size of 2.9µm matches it reasonably well with a Schmidt-Cassegrain with a Barlow, or even a Maksutov-Cassegrain.
It also has a nifty party trick - it's highly sensitive in infrared light, so you can take some specialised photos with an IR filter (the QHY version comes with one in the box). The Bayer filter (which makes the camera colour-sensitive) is transparent at this wavelength, so you get the advantage of a super-high resolution monochrome camera as well!
I have personally used (the QHY version of) this camera and had a lot of success.
The 462 pair beat out the QHY5-III 178C / ZWO ASI178MC pair and the ZWO 385MC. Both these cameras have slightly different sizes, sensitivities and pixel sizes. Depending on your focal ratio and focal length, they might be better suited to your scope.
Cameras for deep-sky work
Deep-sky objects are larger and dimmer. This means you'll be wanting a larger sensor to get your target in the frame. In addition, you're going to want the camera to be more sensitive (all those pixels are like tiny telescopes, each with their own aperture, and the larger sucks in more light), larger pixel sizes are what you need.
For deep-sky work, your exposures are going to be longer to cope with the darkness of your target. Basically, you're going to be getting as long an exposure as you can, before it gets harmed by noise or poor mount tracking. Because of these long exposures, download speed isn't so much of an issue - you're not going to be downloading that many images.
I'm having trouble with a recommendation here. The problem is that deep-sky astrophotography is challenging and entry level cameras are going to have problems.
My choice is the ZWO ASI183MC. This is quite a sensor. First, it's 13.3x8.9mm, which is the largest around in the price bracket. It's also very high resolution, with 2.4µm pixels. This means two things, first, a slow download, which isn't an issue, and second, low sensitivity, which might be. Despite the Sony IMX183 sensor being back-illuminated (look that one up yourself), you're going to have to get long exposures to get a great image, which result in "amp glow" problems (again, look this detail up yourself).
An excellent alternative is the QHY5-III 174C. Its sensor is nearly as large, at 11.3x7.1mm sensor, and it has huge 5.86µm pixels for high sensitivity. It has a few disadvantages though, first, it's expensive, and over the A$1000 target I set before. Second, at 1200x1920 pixels, it's not very high resolution. Your images will look great on a computer screen, but you're probably not be able to zoom in much.
Cameras for the Moon
If planets are tiny and bright, and deep sky targets are large and dim, the Moon is large and bright. Of course, this means it's the most photographed target of all. It's where everyone starts. But even then you've got a choice - whole disk or close-ups?
If you want to fit the whole moon into your photo, you'll need to carefully check to see which sensor size matches your telescope's focal length. There are field of view calculation websites that will do this for you, but it's going to be a pretty large sensor, probably the ones I mentioned for deep-sky imaging.
On the other hand, if you don't mind making a "mosaic" from multiple images, or you want to zoom in to craters, my definite recommendation is the QHY5-III 462C. Use the bundled IR filter with this camera (the ZWO equivalent doesn't come with the filter) to get stunning lunar close-ups. The Infrared filter will improve "seeing" because light of those wavelengths seems to be less susceptible to the atmosphere. The images will be monochrome, but, well, so is the Moon, pretty much!
For many of us, $1000 is a bit much to lash out on a camera. Is there a colour one that will do a rough and ready job? Sure, the answer is yes. At under $300, the ZWO ASI120MC-S or QHY 5L-II-C will get you very decent pictures of the Moon and, with the right telescope, the right software settings and some practice, Jupiter and Saturn.
These cameras both have 4.8x3.6mm sensors with have 3.75µm pixels. I use the monochrome ZWO version as a guide camera.
This article is going to get a bit detailed at times, and to save you reading it all, here are the key recommendations.
With your first CMOS camera, you're going to take some great photos.
Don't assume that your first camera will be your last, though. Practice with this camera will improve your skills in image capture and processing, as well as how to use your telescope and especially the mount. Believe me, you'll get better quickly, and sooner or later you're going to want to upgrade your camera. This is when you'll consider cooled cameras, or monochrome cameras with colour filters, or even better, narrowband filters.
I'm no master of this art, and I expect that many people starting today will become far better than I am. It's a matter of practice and experience.
Good luck, and enjoy the night!