Star trails make for an impressive astrophoto. Image Credit: iStock
Photographing the deep sky is now surprisingly easy.
Armed with a DSLR (digital single lens reflex) or mirrorless camera on a tripod-mounted tracker, even novice astrophotographers can capture great shots of star clusters, nebulae, galaxies and other deep-sky objects.
This is thanks to a new generation of simple equatorial mounts designed for cameras rather than telescopes, which allow a simple tripod-and-tracker setup that’s both affordable and portable.
Let’s explore this setup and photograph a star cluster, a nebula or galaxy! Here’s the essential kit you’ll be using:
You’ll need a DSLR or mirrorless camera with a manual mode.
Since deep-sky objects are faint, imaging them is about opening the shutter for as long as 90 seconds (in our setup) to allow as much light as possible to hit the camera’s digital sensor.
You’ll also need a 38mm ball-head mount so that the camera can move independently of the tracker once it’s in a fixed position.
The star tracker
Earth rotates fast – at almost 1,600km/h – and since we’ll be taking long-exposure photographs, your camera needs to move in sync with the stars to prevent them from appearing as blurred trails on your photos.
So you’ll need a small EQ3 equatorial mount (about £150) or a lightweight tracker like the Sky-Watcher Star Adventurer or iOptron SkyTracker (about £250).
“They’re simple motorised equatorial mounts aimed at astrophotographers,” says Allan Trow, manager at Dark Sky Wales (www.darkskywales.org), who teaches astrophotography workshops.
“They’re very portable and the polar alignment is easy.”
He suggests avoiding altaz mounts, which don’t track the sky in a smooth motion.
Sitting between a camera and a tripod, these trackers initially need to be aligned to Polaris, the Pole Star.
For astrophotography, the star tracker is positioned between the camera and the tripod.
Credit: The Secret Studio
With a relatively basic star tracker, you can experiment with both wide-field and medium focal length DSLR lenses.
What you use obviously affects magnification. That in turn affects the amount of blur in the finished photo; wide-angle lenses can be used for much longer exposures than telephoto lenses before stars begin to trail.
The trackers we’ve mentioned can support anything up to about 600mm lenses.
Now aim for the stars
Three popular targets for beginners are the Perseus Double Cluster (NGC 869 and NGC 884), the Orion Nebula (M42) and the Andromeda Galaxy (M31).
The all-in-one portable star trackers don’t have built-in autoguiding software, though you can add an autoguider to any EQ3 mount.
“It’s not so important because most people go for objects they know to begin with, that they can find themselves,” says Trow.
The easiest way to get great results without spending hours processing images is to take one, long-exposure photograph of your object of choice.
Experiment with shutter speeds up to about 90 seconds.
“With a 600mm lens, 90 seconds is as long as you’ll get before stars start to trail, but that’s more than enough for most deep-sky objects, particularly since newer cameras can bump up ISO,” says Trow.
Use a variety of settings – including different levels of white balance – and you’ll soon learn what works best for different lenses and targets.
As you become more experienced, you may want to experiment with longer exposures, and ‘stacking’ your images to increase contrast, which means using more expensive equatorial mounts that are also more complicated to align.
But armed with the relatively basic astrophotography setup we’ve described here, you can be taking stunning images in no time.
Snowdonia Dark Sky Reserve. Capturing images under dark skies can help you get the astro image you’re aiming for.
The basics of taking your first photo of a star cluster, nebula or galaxy
Conditions & location
Naturally, you’ll need dark, clear skies, but astrophotography also requires good ‘seeing’ (a lack of atmospheric turbulence) and ‘transparency’ (a lack of the moisture and dust in the air that typically occurs after heavy rain).
Perfect conditions will greatly improve your final photographs, but so will advice from experienced amateurs, so a good place to begin your astrophotography adventure is at your local astronomy club.
You need to focus your camera and align the tracker.
Finding the infinity focus point on your lens is best done before it gets dark by auto-focusing on something as far away as possible, using ‘live view’ to magnify the image.
Mark where infinity focus is on your lens then switch it to manual focus.
Now you need to perform a polar alignment using the tracker’s built-in polarscope, though its built-in spirit level is also important.
“Always make sure the tripod is level otherwise your tracking will be out immediately,” says Trow.
Now orientate the polarscope generally towards Polaris.
Where exactly Polaris must be positioned on the tracker’s polarscope clock face depends on your latitude and the time of night; free smartphone apps like Astro-Physics PolarAlign and Polar Scope Align will give you a simple visual guide.
Once that’s done, lock the position of the tracker securely.
You can then swing the camera towards your chosen deep-sky object.
All photography is about balancing aperture (which controls how much light reaches the image sensor), ISO (which controls the light sensitivity of the imaging sensor) and shutter speed/exposure time (which controls how long the image sensor is exposed to light).
Start with an aperture as wide open as the lens goes (perhaps f/4.5 for a zoom lens or f/2.8 for a wide-angle lens). ISO 100 is used for bright conditions, so consider ISO 800
for astrophotography for more sensitivity, though ISO 1600 or 3200 may work better depending on how advanced your camera is.
For the shutter speed, begin at 30 seconds and build up.
Whatever your settings, it’s crucial not to introduce camera shake, so use a remote shutter release cable, rather than pressing the button on the camera itself.
Taking the shot
For the likes of NGC 869 & NGC 884, M42 and M31 try a variety of settings and see what works best.
If you’re using a wide-angle lens, you could also try for a long exposure on the Milky Way in late spring and summer.
Whatever you do, always shoot in RAW rather than JPEG so that you can use photo editing software such as Photoshop or Corel to produce a brighter, more detailed image. It makes a massive difference.
Jamie Carter is the author of A Stargazing Program for Beginners