How to get the most out of star trail photography

Star trail photography - Image © Christina Goggi

Star trail photography - Image © Christina Goggi

I have always been fascinated by astrophotography but never found the courage to go in the middle of nowhere for an entire night to take shots. So when the editor asked me for a photography tutorial I thought to myself, “What would I want to read about and learn myself that I could share with my readers?” It was the perfect opportunity to brave the night and, together with my partner, who is also a photography enthusiast, go on the quest for some star trails.

In this tutorial I will be taking you through what I did to get the final shot here as well as what I learned for the many other star trail shots to come. After all, practice makes perfect and this was only a first.

What you need

  • Camera (one able to take long exposures);
  • A fast (f/2.8 for example) wide-angle lens;
  • Remote shutter release;
  • Tripod;
  • A fully charged battery;
  • Clear skies with minimal light pollution;
  • Time, and lots of it;
  • Thermos flask with coffee, warm clothes, something to sit on and something to keep you entertained (that is, unless you’re not into meditation – if you are, you’re in for a treat).

Preparing for your star trail photography

Your shoot preparation is probably the hardest part of star trail photo­graphy. I would almost go so far as to say you need all the planets to be aligned to get the perfect circumstances for a great result. Timing is everything.

Location is a key factor. You need dark skies, so stay away from light pollution and schedule your shoot for a day when the moon isn’t around. You also need clear skies and as little wind as possible.

When photographing star trails (or any type of astrophotography really), light pollution is one of the biggest factors that can ruin a potentially amazing shot.

To shoot crisp looking star trails without that unwanted night sky glow of artificial light in your shots, make sure you get as far away from light pollution as you can. That’s quite a challenge in Malta, but with a little scouting there are a few spots that are suitable for star trail photography.

Your next step is planning the timing of your shoot. Another form of light pollution that may prevent you from getting good results on your star trail photography adventure is the moon. If it’s around and visible in the sky, it will drown out any visible stars so plan to shoot on the day of the new moon. You can get away shooting a few days before or after new moon as long as you frame your shot well away from where the moon is visible.

The weather also plays an important role in the end result. If any clouds are visible and passing through your composed shot you’ll be photographing cloud trails rather than star trails, while shooting on a windy evening will be challenging (if not impossible) because that will cause camera shake and therefore images that aren’t sharp.

Finally, although it’s hard to avoid humid nights in Malta, humidity can cause a hue in your images, making the stars appear less bright than you’d want them to be.

Getting the shot

Your aim is to get a series of 30-second exposures, which you will then blend together in post-processing to create your final star trail shot. One very long exposure (in BULB mode) is possible too, but that will cause the sensor to heat up, which may cause hot spots to show on your final exposure. I went for the former with mine – I will explain later on why this was an excellent choice later as first, we need to focus on the steps.

Step 1: Select the right settings

Select manual mode to avoid changes in exposure between shots

Select a white balance setting.

Check that the battery is fully charged, as well as the batteries of your remote trigger (if it uses any)

Set your shutter speed at 30 seconds and select the maximum aperture of your lens, paired with the ISO needed to get well exposed 30-second shots. The guidelines for common apertures are:

f/1.4 and ISO400 = 30s;

f/2.8 and ISO1600 = 30s;

f/4.0 and ISO3200 = 30s;

f/5.6 and ISO6400 = 30s.

Set your camera drive to continuous shooting so that shots are taken with minimal interruption and you can have a cup of coffee in the meantime.

Shoot in RAW so you have more options when it comes to post-processing, if you need to tweak white balance and exposure, for instance.

Step 2: Positioning your camera

For a sharp, long exposure, make sure you use a sturdy tripod on a firm surface. Then, look around to find the Northern star (Polaris), to be able to predict the direction of star trails and help you better position your camera and frame your shot. For this, I used Google Sky Maps (Android app), which uses your phone’s gyroscopic sensor to show you in what part of the sky you can find particular stars, constellations and planets. Search for ‘Polaris’, point your phone towards the sky and follow the app’s guideline to find this bright star. If you’re an iOS user, an alternative app is called Planets.

Step 3: Setting up your other gear

Lens: You’ll want to use a fast lens, and depending on the environment, a wide focal length such as 16-28mm.

Remote shutter release: Ideally, use a remote shutter release to avoid introducing camera shake (which can affect sharpness) and to make it easier to take successive 30-second shots by being able to keep the shutter button pressed continuously. You can always use a piece of duct tape to hold down the shutter button on your camera, but remote shutter releases aren’t very expensive.

Step 4: Start shooting!

First you need to focus. Point at Jupiter or a bright star and use your autofocus to lock focus. Then switch to manual focus carefully. Manually adjusting your focus ring to infinity rarely works.

Frame your shot. Although the star (pardon the pun) of your shot is the actual star trails, consider adding something of interest on the horizon or in the foreground. That doesn’t necessarily need to be a lit subject – it can also be an easily recognised silhouette.

You will want to get at least 50-60 photos (which takes 25 minutes in all), though experiment and you’ll learn what number of shots works best for a given situation. Of course, the more shots, the longer your star trails will be.

Take a few test shots to start with, to make sure your composition looks good and the exposure you get is spot on. This can be tricky. If you don’t have a fast lens (f/2.8 or lower) you’re going to have to play with ISO. You’ll need to find a balance between getting low-noise, yet well exposed images. Always keep in mind the stars are the star of the show (yes, again, pun intended), so although foreground objects need to feature in the image, if you give the foreground too much prominence you will introduce noise into the sky part of your image.

If you have a remote trigger, press the shutter button and put on the shutter lock (a mechanical function most remote triggers offer) and for the next 30 minutes or so you can find a way to entertain yourself.

After quite a few hours and takes, it’s finally time to go back into your cosy home. If you’re as eager as I am though, let’s move to the next stage.

Post-processing

Here is where the fun starts and where all that time out in the cold in a dark, deserted place pays off.

There are a few methods to process your images. The first is using Adobe Bridge and Adobe Photoshop. Manually editing your shots and blending them together in Photoshop takes time and patience, especially if conditions during the shoot weren’t perfect. Having said that, the result you can achieve are worth it considering the time you’ve invested in taking the actual shots.

Start by editing the first RAW file in the series of shots you took to make your adjustments, then synchronise those adjustments across all images. Load all images as layers in Photoshop, making only the bottom layer visible to start with, setting the layer mode to ‘Lighten’. Go through all other layers, making them visible one by one and switching the mode to ‘Lighten’. As you go through your layers you can easily touch up any flaws, such as the odd airplane passing through a few of your shots.

If you feel your blended image needs it, add a layer mask to edit the foreground separately from the sky.

Another method is to use software that is specifically built for star trail photography. Tools like StarTrax that will automatically line up all your images and blend them together to get a good looking end result. The two downsides are that you will still need to edit your RAW images, then export to JPEG, and that any flaws like the streaks of an airplane passing through your shot would show in your final image.

If you don’t have too many flaws in your shots and only basic touch ups are required, this is a fast track to getting to the finish line. If, however, more than basic editing is required or you simply want to get as close to perfection as possible, do it the manual way.

The final photo

I know, it isn’t flawless and there’s room for improvement, but it being a first attempt I’m pretty pleased with this. In fact, I’m already planning my next star trail photo­graphy session.

So here are some other things I’ve learned from his experience which I’ll share with you:

Planning and waiting patiently for the perfect circumstances is vital.

Having a limitation of a maximum aperture of f/4 on my wide-angle lens, I can confirm that a lens that will allow you to shoot at f/2.8 (or wider) will give you far better results. With a smaller aperture you inevitably need to increase your ISO, which results in noise.

Proper post-processing can go a long way to reduce noise but starting off with visible noise already puts you on the back foot.

Be wary of light disturbances. It paid off to go for the series of 30-second exposures as I had cars driving up to one of the most remote locations on the island with brights on full blast – so I could remove the ruined shots and still get the right final image with processing. Having said that, next time I’m going to an even more isolated location. You can’t stop planes from flying by but if you can foresee and avoid any potential deal breakers, do so.

I should have gotten a thermos with hot coffee – we basically went to take the shots straight after work so none of us thought of food and drink. A nice warm cup of coffee would have been lovely as you’re waiting for the series to reach completion in pitch darkness and the cold.

I hope this has inspired you. Now go reach for the stars.

Article first published in Tech Sunday, Sunday Times of Malta, April 6, 2014

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