Seeing a planet, nebula, or deep-sky galaxy for the first time is exhilarating.
Unfortunately, the experience is also fleeting. Sure, you can probably find it again, but perfect viewing conditions are hard to come by. Nor is there any way to share your discoveries online or at a meeting of your local astronomy club.
Hooking a camera up to your telescope solves this problem, but, as you’ll soon see, there’s a huge difference between a skillfully taken photo and one that screams: “Trust me, it’s Saturn”. Like food and portrait photography, the art of taking pictures of the heavens requires some special equipment and techniques.
Neither of these are unattainable, though, and learning the ropes will make you a better photographer as well as astronomer. The more you know, the more fulfilling this hobby becomes. Just don’t expect it to be easy: working within the limitations of a hobbyist telescope requires some patience and ingenuity, which is why astrophotography contests are at least as competitive as those dealing with wildlife.
Are you ready to get started?
Can’t I Just Use My Selfie Machine?
Surprisingly enough, a couple of telescopes actually allow you to take middling-to-fair photographs using nothing more than a cellphone. This may be done using a dedicated bracket, or you could hold your breath and simply try to keep the phone steady over the eyepiece.
This is all very convenient for taking happy snaps to put on your Facebook page, but you’ll definitely run into problems as soon as you try to do anything more complicated than pointing and clicking.
Impressive megapixel numbers aside, nearly all smartphone cameras suffer from the following drawbacks:
- Poor light sensitivity: Cramming as many pixels as possible onto a tiny sensor means that each CMOS or CCD cell has to be smaller. Combine this with being able to fit no more than a micro lens into the phone’s body, and you can see that only bright objects can be photographed. Most phones’ lack of dynamic range is also a problem: any bright object in your field of view is likely to wash out dimmer details.
- Low resolution: It’s easy to confuse pixel count with resolution, but the fact is that a high PPI count doesn’t necessarily mean being able to discern fine image features. Cheap, miniaturized optics just aren’t capable of displaying a clear image at a scale of only a couple of pixels.
- No control over basic functions: Smartphone cameras typically don’t allow you to set exposure times, focal length, aperture, or even focus manually (autofocus tends to struggle in low-light conditions). There’s just no way of producing high-quality sky photographs without some amount of tinkering around with these settings.
- Automatic image processing: Few if any phone-based cameras allow you to export a picture in RAW format. Instead, every photograph is color-corrected, sharpened, filtered, stabilized, compressed, and generally fiddled with. All these algorithms are optimized for taking pictures of pets, landscapes, and birthday parties, and are therefore likely to obscure important sky details and add random artifacts of their own.
Stuff You’ll Need (or Want) to Buy
While it’s still possible to have fun for free, most serious hobbies do require you to spend some money if you want to get anywhere with them.
Don’t let this aspect of astrophotography discourage you, though: even a relatively modest setup can produce amazing results in the right hands, and there are often bargains to be had if you keep an eye on the second-hand market.
A Telescope
This may seem too obvious to mention, but aside from wide-angle shots that show more or less what the naked eye can see, a telescope of some kind is a must for astrophotography. Telephoto lenses are cool enough in their own right, but they’re just not optimal for taking pictures of celestial scenes (though it is certainly possible to take some stunning night landscapes without a telescope).
The effective magnification of an ordinary lens is only about its focal length (in millimetres) divided by 50. It’s difficult to focus it with the precision needed to really make stars pop. Their light-gathering ability is limited, and, unlike a reflector telescope or apochromatic refractor, they’ll generally produce a noticeable color fringe around stars or cause larger objects to appear fuzzy:
In much the same way, many hobbyist scopes can’t hold a candle to those designed with photographers in mind. At a minimum, you’ll need one capable of accepting a T-adaptor, but this by itself is no guarantee that a telescope is able to take good photographs. If possible, search online for images taken with whichever camera you own using a variety of telescopes.
Aside from this, the kind of objects you’d like to photograph also plays a role in determining which type of telescope will work best for you. If distant galaxies are your thing and you don’t plan on doing long exposures, a Dobsonian might be just what you need. Many photographers, on the other hand, insist that nothing beats an apochromatic refractor (though these are pricey) when it comes to bringing out fine detail on planetary surfaces and double stars.
Most importantly, remember that your choice of telescope will play a major part in determining your field of view: the longer its focal distance, the narrower the frame will be. A wide-angle telescope is much more forgiving and therefore a better choice for someone just starting out with astrophotography, especially if not using a tracking mount.
An Equatorial Mount
The better your mount, which is what the platform that fits between your tripod and telescope is called, the longer you can leave the shutter open. Without the ability to track objects across the sky, exposure times of a minute or more will result in planets turning egg-shaped or noticeable star trails appearing in the background. The thing to know here is that as the earth turns the sky not only moves sideways but rotates, as these star trails show:
It’s easy to compensate for this as long as you have the proper equipment. The basic idea is to align a specially designed mount parallel to the earth’s equator and use a small motor to turn it at just the right rate to keep whatever you’re photographing properly framed.
Some telescopes are fitted with an equatorial mount as standard, requiring you only to buy the motor and control electronics. You can also find tracking mounts that are capable of accommodating a wide variety of tripods and telescopes.
Go-to drives, which allow you to find any of thousands of celestial objects with the touch of a button, tend to cost a little more. Digital autoguiders, for their part, use a secondary camera plugged into the finder scope to keep the image wonderfully stable, but can by themselves cost as much as a mid-range DSLR.
Steadiness is key here: it’s extremely important to select a mount that can handle (and not just barely) your telescope and camera’s combined weight.
A good rule of thumb is to load up a mount and tripod with no more than half the weight it’s rated to carry, or anything from a light breeze to nearby footsteps will produce noticeable camera shake at high magnifications. Some useful tricks are to extend your tripod’s legs only partway, or hang something heavy from the center to anchor it in place.
Additionally, you will probably want to select one with a counterweight to balance its load accurately. This improves not only the stability of your setup but also makes your tracking drive work more precisely due to less strain being put on its gears.
A Camera
Pretty much any DSLR camera with a manual exposure mode can be used for astrophotography – many people, for instance, have achieved good results with something like the Canon Rebel series.
A more expensive, more capable camera will obviously produce better images, but exposure time is pretty much the single most important factor when it comes to photographing deep-sky images. If you can, it’s worthwhile to look at models that can be controlled via a USB connection to a computer without having to hover over an intervalometer, or at least get a remote shutter control to minimize vibration.
If you’re able to spend a little more, the best policy is to look at models capable of high ISO imaging with a low signal-to-noise ratio (SNR), meaning the ability to produce photos in low-light conditions with a minimum of graininess or snow. Should noise continue to be a problem, a tracking equatorial mount allows you to balance lower ISO numbers with long exposure times. It’s actually not uncommon for deep-sky photos to be taken over more than one night before the final image is assembled using stacking software (as described later on).
The ultimate in boosting your SNR ratio is buying a dedicated astronomical camera with a specially cooled image sensor. The principle at work here is that CCD and CMOS sensors get hotter the longer they’re activated, which increases noise (and not equally across all pixels!). This is the kind of gadget that astrophotographers dream of, but most beginners will prefer to spend the money elsewhere, probably on a more capable mount or telescope.
Filters
Probably sooner rather than later, you’ll want to start using filters to increase the contrast and usable resolution of your images. You can most certainly do without these, but since they’re relatively cheap, versatile, and easy to use, you might as well grab a few and start experimenting.
When it comes to astrophotography, you basically have three options:
- Eyepiece filters,
- Clip-ons that fit into the camera body,
- And those that screw into the T-adaptor.
The exception is solar filters, which always go over the objective end of a telescope. Unless you live way out in the sticks, you’ll almost certainly want a light pollution filter to start with, while narrowband filters are fantastic at bringing out the details of certain nebulas.
On a related note, many people modify their DSLR’s for astrophotography by removing the IR cut filter inside, which allows the deep-red hydrogen-alpha color that characterizes many nebulas to pass through. This will, unfortunately, give your daytime images a reddish hue, but this can be fixed in Photoshop. More significantly, the warranty on your camera will go out the window as soon as you pick up a screwdriver.
Odds and Ends
There are a few other attachments and gadgets that can make astrophotography a lot more rewarding. For the most part, these are mentioned in the sections where they fit in naturally.
Just remember: the guy with the biggest box of toys does not necessarily take the best pictures. Instead of buying every shiny gizmo out there, take the time to learn about the capabilities and limitations of each, then expand your collection only as you realize that you need some specific piece of apparatus.
The Ins and Outs of Taking Sky Photographs
As you’d expect, there’s a huge overlap in the skills needed to operate a telescope and those used to take good astronomical images.
The very best advice for a newbie at celestial photography is to learn these basics before trying to, as it were, reach for the stars. This may mean putting off what you’re most interested in doing until a later date – but, trust us, this will be time well spent.
Looking Ahead
One key factor in achieving great astronomical shots is to plan everything in advance. Ideally, you’ll know what you want to photograph and what gear you’ll need to do that, and to have everything set up by the time the sun goes down. The last thing you need is to have to fiddle with unfamiliar cables in the dark, or even consult the user manual by flashlight.
Finding Sky Objects
The Stellarium app allows you to set up your shots, virtually, well in advance. Simply use the Oculars plugin, enter a couple of details regarding your camera and telescope, then select a target from the built-in database and see how the frame will look at a given focal length.
You’re actually spoiled for choice when it comes to digital astronomy tools, including those that use augmented reality interfaces to tell you what you’re seeing and others that practically include a full beginners’ astronomy course in a fun, easy-to-use format. A few can even run your go-to drive as long as you have the proper accessories.
Seeing If the Elements Will Play Along
It sucks if the only time you have available for taking photographs of the sky is on Thursday evening between 9 and 12 pm and it turns out that it’s overcast during that window. The majority of weather reports are more concerned with whether or not it’s going to rain; things like haze or turbulence in the upper atmosphere just aren’t relevant for most people.
Luckily, there is a technological solution to this in the form of weather apps designed specifically for the needs of amateur astronomers. These are far from perfect, but they do take some of the guesswork out of scheduling your sky photography sessions.
Blue Skies Aren’t Always Best
Light pollution, too, is something that can ruin an evening’s work. You can save yourself a ton of bother by checking the moon’s phase and position in advance using Moongiant, but you may also need to pack a bag and get out of the city for really optimal conditions.
If you’re interested in a weekend astrophotography getaway, there are a couple of terrestrial light pollution maps you can consult to find a nice camping spot that’s hopefully not too far from home.
Two Techniques
In terms of what you need to do to use either successfully, these techniques are very similar, so you’ll probably switch between them at need.
Eyepiece Projection
Simply aligning the camera with the eyepiece allows you to take good shots of moonscapes and most planets by making use of the extra magnification the ocular (and perhaps a Barlow lens) provides. This significantly increases the effective focal length of the whole optical assembly, but comes at the cost of a higher /f number.
This means that you’ll need to either crank up the light sensitivity or else opt for a longer exposure time. In the latter case, distortion due to atmospheric turbulence will also be magnified, as will any mount vibration, so there are practical limits to what you can achieve using this technique.
Hooking up a DSLR camera to a telescope is fortunately easy, assuming that the latter supports it. All you’ll need is an adaptor and eyepiece holder from the telescope manufacturer as well as a T-ring specific to your brand of camera, perhaps along with an extender tube in case your telescope can’t focus without some additional space with which to work.
You may also want to buy a field flattener, which helps to reduce the apparent curvature of your image that will distort stars near the edge of the field of view into oblong shapes. This becomes especially important with wide-angle shots like this:
Prime Focus Astrophotography
Using the inherent, or prime, focal length of your telescope without an interchangeable eyepiece works best for deep-sky observations. This basically trades some magnification for a brighter image containing more vivid detail.
Essentially, this makes a scope with a 1,000 mm focal distance behave much like a telephoto lens of similar size, allowing you to figure out what kind of magnification you can expect given your camera’s sensor format.
Configuring Your Camera
The low price of general-purpose DSLRs brings astrophotography within nearly everyone’s reach. Unfortunately, their designers typically don’t think of far-off galaxies ahead of landscapes and other common scenes, so you’ll need to make a couple of tweaks for best results.
Turn off image stabilization, long-exposure noise reduction, and any other digital trickery your camera may be capable of. Unless you are lucky enough to own one specifically designed for taking pictures of dark skies, these will hinder rather than help. You may also want to activate your DSLR’s mirror lock if it has this function, as even the slight twitch of the mirror flipping up can cause your setup to shake slightly.
Since much of the art of producing good photographs of the night sky involves post-processing, always store your images as RAW files. This, among other things, allows you to correct the white balance later on.
It’s also a good idea to check your camera’s histogram before starting to shoot: if neither the darkest nor lightest parts of the images are being cut off, you’re making good use of your image sensor’s dynamic range. Conventional HDR techniques don’t really work in astrophotography, though there are workarounds you can use.
Telescopes can be finicky beasts, too. Remember: along the whole path light has to travel, errors will multiply. Putting a $10,000 camera on a scope that’s been set up carelessly will not give you stellar results. Fortunately, getting this part right is not very difficult once you get the hang of it:
Choose a bright star to adjust the focus; just get the image as small as possible. Take a few minutes to make sure your equatorial mount is aligned as precisely as possible – doing a slapdash job at this stage can ruin all of the photos you take subsequently. The same thing goes for careful collimation in case you have a reflector-type scope. This, aside from any other concerns, makes a good refractor the better choice for most beginners.
Even if you do everything by the book, you’ll probably find that experience is your most diligent teacher. Finding the right combination of ISO setting, f-stop, and other factors for different circumstances always takes a little trial and error. There are a couple of guidelines that generally produce good results, but feel free to play around with these, always take notes so you can see what works best, and be sure to pat yourself on the back every time you notice your pictures getting better.
Making One Picture out of Many
The single greatest thing about digital cameras is that their film is so cheap. Clearly, taking 50 photographs makes it that much more likely that you’ll end up with two or three really good ones. Even if none actually look like anything at all, you haven’t necessarily failed. Taking the time to do things right while you’re out under the stars is certainly indispensable, but it’s often post-processing that makes the difference between a mediocre picture and a skygazing souvenir you can be proud of.
This is true for professional and scientific astrophotography too. The recent images of a black hole, for instance, had much more to do with teaching computers to interpret data than knowing where to look. Many of the most beautiful astronomy images are created by combining pictures taken by two or more telescopes, or even displaying invisible parts of the electromagnetic spectrum.
In general, deep-sky objects require total exposure times of 2 hours or more to really look their best. This may be captured during one night or over several, but achieving the best detail and color in post-processing absolutely depends on beginning with as much crude data as possible. The best way to get it, as it turns out, is not a single long exposure during which there’s plenty of time for things to go wrong, but taking multiple photographs with a shutter interval of perhaps one to 30 minutes.
Assuming that your camera supports it, you can also accomplish something similar by shooting video instead of still images. A movie clip lasting a couple of seconds can be de-composed into hundreds of individual frames using a program like Registax, though your pixel count will, of course, suffer.
The Three Types of Calibration Frames
The bulk of post-processing is all about highlighting the features you want while removing everything that doesn’t belong in the picture. Calibration frames allow specialized software to figure out which of these is which.
“Stacking” images averages out random noise while effectively increasing the length of exposure, without the undesirable effects of simply keeping the shutter open longer. Specifically, running your camera for lengthy periods of time causes the sensor to heat up and produce more noise. It also multiplies the risk of external vibrations and flaws in the tracking system, spoiling your photograph.
The following are some shots you’ll want to take along with your image frames. A good rule of thumb is to take ten to twenty of each. This may seem tedious, but the results are well worth it.
Dark Frames
Forgetting to take off the lens cap before shooting is the subject of many bad jokes, but it happens to be exactly what you should do to compensate for the random thermal noise produced by all digital cameras. Every pixel on an image sensor isn’t equally sensitive; determining the output of each without any light falling on it can give your computer a good idea of how they behave in practice.
Snapping a dark frame is perfectly simple: just cover the lens and even the viewfinder, make sure the camera and environment are at the same temperature as when the original pictures are taken, and snap a couple of rather uninteresting photographs using the same exposure time and ISO you used for the image frames (or light frames, as they’re often called).
Flat Frames
Most lenses, including those used in telescopes, work best at concentrating light at the center of the image sensor or eyepiece. This makes the outer edges seem darker, a phenomenon known as vignetting:
In addition, flat frames help a little when it comes to eliminating imperfections caused by fingerprints and dust on the sensor or lens. The basic idea is to take a few pictures of a completely evenly lit field such as a cloudless daytime sky or painted wall. A useful trick here is to stretch some white cloth with a fine weave over the telescope’s aperture to help diffuse the incoming light evenly. Since this is all about focus, you’ll need to set all camera parameters the same as those the actual photos were taken at and shoot your flats through the telescope.
Bias Frames
Your camera’s electronics don’t read all parts of an image in the same way; electrical interference and other types of electronic noise cause minor variations between pixels. Fortunately, accounting for this is fairly easy.
All you need to do is cover the front of your camera, set the shutter speed to the shortest possible value, and snap a few frames. Note that the bias signal is actually contained in the dark frames, too, but since DeepSkyStacker and similar programs support bias subtraction, and adding bias shots to the mix takes little time, you might as well use them. You will notice an improvement, particularly when it comes to color correction.
Integrating a Series of Pictures
There’s a whole mess of image processing applications out there, from Photoshop and Lightroom to packages that specifically cater to astrophotography tasks. DeepSkyStacker is the favorite tool of many: it’s totally free to use yet remarkably powerful, and there’s a huge community of users willing to share their experiences and insights.
Though using DeepSkyStacker to its full potential requires a bit of know-how, combining multiple light (image) exposures, removing the dark and bias signals, and compensating for variations seen in the flats is mostly a plug-and-play process. The math involved behind the scenes is quite complex, though: it’s best to expect each job to take at least a few minutes and not yell nasty things at your computer.
Once this is done, you will probably want to turn to a more full-featured photo editing suite to spice up the image. This is one instance in which it’s definitely worth paying more for the best software, as well as a book or course to teach you how to drive it.
There really isn’t any simple, universal recipe for manipulating a photo from so-so to something amazing. Read about what has worked for others, adjust the light curve, nudge color saturation one way or the other, and try applying tricks like dithering. If you get frustrated, remind yourself that you’re now capable of enhancing images in a way that simply wasn’t possible a few short years ago – and you can perform this magic without having to brave the cold and dark outside.
Patience, Patience, Patience
Astrophotography is not all that easy; don’t expect your first or even your fifthteenth attempt to come out just the way you imagined. With a little study, practice, and experimentation, however, you’ll soon start climbing that learning curve. There’s no real substitute for doing so: it’s just not possible to get good results by substituting money for effort.
You might, for instance, start by spicing up your night landscapes by making sure the Milky Way is visible in the background before moving on to wide-angle deep space images and later capturing distant star clusters and nebulas. You’ll probably find that there’s more to astrophotography than you ever thought possible, but also that the skygazing community is a very helpful one, with tons of free resources available to people of all skill levels.
