It has been said that viewing a star trail image is like watching an entire movie on one frame. That’s a notion I find incredibly fascinating. To see time compressed in this fashion within a still photograph evokes thought about all the events that may have occurred during that period. This begins to get quite interesting when you think about the planet as a whole; the contrast with the other side of the globe, immersed in daylight and busy with the billions of daily routines in activity. The image above was taken on the coast of Exmoor, across the Bristol Channel. From left to right, from Newport to Tenby; almost the entire width of Wales is visible for around an hour’s duration. Imagine how much happened in that country during that time.
Star trails are a personal favourite if you haven’t already noticed. Photography involves the capture of time as a fundamental element but star trails allow a photographer to take an extended period of time and use it as a new dimension to work within an image, with dramatic aesthetic results. These images are created with fairly standard digital methods, usually involving multiple successive frames merged into one final image. The technique has become most of what I do and has been for a number of years now so I feel quite confident in writing about the process to help anyone who may be interested in giving it a try.
I do not intend to create a definitive guide here but instead a fairly detailed introduction to my way of working coupled with whatever imagery I have to hand. It would be too simple to briefly run through the technical aspects of how to create one of these images for yourself but I believe that describing some of the thought processes I go through before the camera is even out of it’s bag would be beneficial to those looking to really experiment with the technique.
I believe planning is one of the key factors towards creating a strong final image. Taking a bit of time to study your subject, the local area, weather conditions etc. can put you in control, allow you to manipulate some vital aspects of your image and use them to match your vision. There are definitely nights where star trails work better than others. That goes without saying, so when it’s cloudy, do some research!
The first thing I hear from people looking to shoot their first star trail is that they’re off to find somewhere really, really, really dark Somewhere completely free from light pollution, hundreds of miles away. Bearing in mind that photography wouldn’t exist without light, I think this is only a good idea once you have mastered the basics. Without a reasonable amount of ambient light you won’t have much there to illuminate your foreground and as a result you will likely push your camera past it’s usable limits to compensate, resulting in an image that looks like your camera has just shat itself. You can shoot a star trail wherever you can see the stars so save yourself the time and fuel by starting closer to home whilst you gain an understanding of the factors at play.
Of course, weather is a vital factor, cloud is a barrier to star trails but if it blows into your image in the right place it can add to the composition… So don’t always pack up as soon as the clouds roll in and don’t necessarily let them put you off going out in the first place. Check the weather as often as you can so you are aware of what’s coming and when.
Shooting under moonlight is not always a bad thing for star trails, in fact I love it. I find my favourite images were created under conditions with either full or partial moonlight. Sure the extra light bouncing around in the atmosphere does sap contrast, fogging the sky but it replaces that contrast with colour. If you can combine the effect of moonlight with light pollution, the mixture of blues and oranges creates vibrant tones in the sky which can add a real punch to the final image, in my eyes. This is a great way to work with a wide landscape. With a close foreground element the effects of the ambient light can be accentuated even more with some carefully considered supplemental lighting from a torch or flashgun.
Heading out on nights with no moonlight will inevitably lead to orange images in most countries. Under these conditions it is difficult to get a strong ambient illumination for my foreground subject so I’ll usually go for a subject which is maybe a bit more sinister and mysterious, aiming for a low key image with the dominant lighting coming from a torch or flashgun, unless I had a great silhouette in the frame. The orange/red tones of dissipated sodium street lighting really suit an aggressive, turbulent image and dark shapes in the foreground can become very dramatic. I would prefer a very clear sky here to reduce the impact of the orange plague; cloud, haze and fog just saturates everything sodium orange pretty much anywhere in the UK. Another option available on these nights is to begin the shoot during dusk, or plan to end the shoot during the dawn twilight so you have some more variance in the sky’s colour palette to work with.
Combining ambient conditions with a great foreground subject is the way forward. A good foreground subject could be either natural or artificial but I often find myself coupling star trails with organic subjects that can demonstrate the passage of time accordingly, such as an old hut becoming overgrown in brambles, or a mountain range, formed over millennia. When you are planning to shoot a subject with star trails in the background, think about the qualities of your subject and how you can use the conditions of the night to best represent them.
How long should the trails be?
There’s no real answer here, It’s subjective. I will stay in one location for a maximum of three hours for one shot and find I get pretty damn restless after that. There’s some great shots out there with trails for six hours or more but I generally find shots like that a bit too busy on the eye. Most of my star trail images span thirty minutes to two hours and I feel that creates a long enough trail without cluttering the frame.
To Polaris or not to Polaris?
It’s undeniable that the circular rotation of the stars around the North Star, Polaris makes it a good direction to point your camera but don’t get caught up in the hype that this is the only direction you can aim at for a star trail. Use the elements in your scene to create the composition you want with a priority on the star trails. Use them as a compositional tool. If your frame looks best facing North towards Polaris then so be it. I like to point my camera all over the sky, but I do find that, being in the Northern hempisphere, looking south creates fairly unimpressive, horizontal trails across the sky so I generally avoid that angle.
To find Polaris, follow the shape of the Big Dipper from it’s handle to the pan. Follow that line onwards and the next bright star is Polaris. Look up star charts, and familiarise yourself with them, there’s more than enough on the internet. Google Sky Maps is a great tool to use in the field, along with many others which all help you get to know the night sky. It is also useful to know how to spot Polaris when you’re navigating your way through the world at night, this is the only star that doesn’t really move with the rotation of the planet, so knowing where it is in relation to your path easily allows you to stick to a bearing.
There’s a few things you need before you head out for a star trail. Firstly, don’t forget the tripod, and don’t forget the quick release plate if it has one either. That’s a pain in the backside, believe me.
You do not necessarily need a DSLR as results can be achieved with a compact system camera such as the Sony NEX 5R with it’s time lapse application or even a compact if you’re really determined. You essentially need manual exposure control and manual focus, with some way of continuously releasing the shutter.
I prefer to use an ultra wide lens. I love the perspective and it allows you to get a lot of sky in the frame, plus you don’t need to worry about pinpoint focusing at those short focal lengths. As the earth rotates, with an ultra wide lens you will be able to capture the stars’ motion after around thirty seconds and there’s even a formula for calculating this in relation to the focal length you are using.
If you are brave and keen on best practice, you can set up for one long exposure of up to thirty minutes on most DSLRs but you may waste an hour or two before you get the exposure right and you’ll certainly need to use long exposure noise reduction, consuming valuable battery power and adding to your time in the field. Best practice really is best, and it is most satisfying to shoot in a single frame, so make sure you try it.
Using a technique called ‘stacking’ which I will discuss in detail below, you can combine multiple exposures into one image, adding the light from each exposure. It’s beneficial to have a good understanding of how the stacking process works before you go out so you can use it to your advantage.
You want every setting to remain consistent with a stacked star trail. Take the white balance off auto, use what ever white balance you want to, just be sure to keep it constant. Keep the aperture set, keep the ISO set and make sure the camera is set to manual focus. Exposure time is the one setting that can vary somewhat, as you will find out. Aperture is probably the only setting I rarely change with star trails and at night this really only varies whether I am using a full frame camera or one with an APSC sensor.
This is an area of photography where cropped sensors are good for night photography as the smaller sensor gives you a larger depth of field at a particular aperture compared to full frame. To make it easier to understand I’ll relate it to the two systems I use most- An APSC Nikon D7000 combined with a Tokina 11-16mm f2.8, and a full frame Nikon D800 mounted with the Nikon 14-24mm f2.8.
Using the D7000 and 11-16mm I can get most of a landscape scene in focus at f5.6, and I can still get pretty close to the foreground to enhance the perspective, without it becoming too blurred. This allows me to shoot with the aperture relatively wide, letting more light in so I can use a lower ISO, and/or a shorter exposure time thus resulting in an increase in image quality, and more time at the end to explore the night.
Using the D800 and 14-24, f5.6 doesn’t give that much depth of field in comparison. I find close elements of my image frequently out of focus which leaves me shooting at f8 to end up with a nice sharp image. This aperture setting gives sufficient depth of field for me but lets half the light in. This means your exposure is now halved, so you can boost ISO to compensate.
A full frame system is far less forgiving for focusing errors, but on the contrary, is far more forgiving when you whack up the ISO. If you’re upgrading to full frame you’ll likely notice your night photography change a lot. For those reasons, dependant upon the camera system you are using, the settings I would recommend starting with are:
Full Frame: f8, ISO 400.
APSC: F5.6 ISO 200.
Then experiment from there. The overall exposure is ultimately up to you but the exposures have to be in rapid succession, shot within about five seconds of each other to avoid gaps in the star trails. I would recommend you do not allow the camera to expose frames longer than 3-4 minutes, otherwise you will get visible thermal noise. This will show up as a purple glow at the edge of your frame, partly caused by the heating of the camera’s internal components.
Another detrimental effect of long exposures are hot pixels, a similar thermal byproduct where individual pixels on the sensor overheat, showing up as bright, colourful points of RGB light. Usually, some form of long exposure noise reduction would be used, but because the process takes the same amount of time as the original exposure, that would mean the stars would move and we would have large gaps in the final star trail where the camera was processing the images. We are after complete, unbroken trails so we want to keep the camera from straying into the zone where noise reduction is necessary. Disable this function in the camera’s menu. The exposure length vs noise is a fine balance and one of the technical aspects my brain computes most while setting up. It will depend on your individual camera model, they all differ greatly and you need to experiment with your own gear so you know just how long an exposure you can get away with.
Triggering the camera
A remote control is needed, whether it is wired or wireless and there are three ways of actuating the camera for multiple frame star trails.
Some cameras have an internal intervalometer, such as Nikon’s prosumer range with the D7000, D7100, D300, D700 and upwards. This can be handy but the feature is limited to a maximum exposure time of thirty seconds which will result in you using a higher ISO to correct the exposure, degrading final image quality.
If you have an intervalometer remote, this can tell the camera to fire, say every thirty seconds for the next three hours. This is good, and far better if you can tell it to fire two minute exposures so you can use a lower ISO for better quality. One hour becomes 30 frames rather than 120, so there are far fewer files to clog your computer with.
If you only have a simple remote, there’s nothing wrong with opening and closing the shutter yourself on bulb mode. Either use a stopwatch, timer, or just guess when your exposure is ready to start again. The final image will have the overall brightness of the longest exposure you shoot and the rest will merge in together to create the star trails.
JPEG or Raw?
The high or the low road? Well I’m always a fan of shooting raw + JPEG just in case I need quick access to the file. When I get home I keep the raw files for my archive most of the time and bin the JPEGs in a vain attempt save space. Your choice of file type is the divide between processing techniques. I’ll explain the benefits of each and run through how I process both formats.
Shooting in JPEG you are restricted. I like to tweak my files in a controlled environment on a computer and you can only tweak JPEGs so far. The advantage of using this format is the speed. If you take care to get everything right in camera at the time of shooting you can end up with some stunning images that don’t require much time, or processing power in your computer. Of course your final image is only 8 bit compared to 16 bit so there is a permanent reduction in quality. Some argue that this is negligible but I believe in taking every possible precaution to maximise image quality, you never know where your work will end up in the future. Make sure all of your JPEG processing settings are tuned how you want them to be in your camera’s menu whilst setting up.
Processing the JPEGs could not be easier and I highly recommend giving this method a try at first. All you have to do is download the star trails software available from www.startrails.de. Open the software, click the button to load your images and then click the star trail button. Because we have avoided long exposure noise while we were out with the camera, we can ignore the dark frame options for now. Either get a cup of tea or sit back and watch your image come together and save it. It may be fun to you, it may be boring, but watching each image falling into place while the software does it’s thing can really help you understand how every little bit of light that hits your scene makes an impact over time whether it is intentional torch light, the occasional passing of a car in the distance or another bastard aeroplane passing through the night sky above.
Shooting in raw allows much more freedom with post processing. I do not advocate heavy photo manipulation myself, I am a fan of ‘real’ photography with minimal processing. I view the effects achievable with Adobe Camera Raw to be a standard digital equivalent to processes available to analogue media in a darkroom and I find it preferable to adjust the files before I stack them. Tonal effects can be applied, pulling back shadow detail which is almost always necessary with night photography, all retaining maximum image quality. Even slight adjustments can make a dramatic improvement to the impact of your final image and all you have to do is apply the adjustments to one file and then batch apply them to all the files you intend to stack, but for consistency it’s a good idea to set a custom white balance in ACR, just in case you forgot to set it at the time or you want to fine tune it.
There’s a great Photoshop action available at Star Circle Academy with clearly written instructions on how to download and use it. Read those and follow them step by step. If you’re not used to, or even intimidated by the actions feature in Photoshop you’ll pick it up within a couple of attempts from the good information on that site and won’t need the instructions again. This action works by selecting all the files in a folder (unless you initiate the process through Adobe Bridge’s Photoshop batch options) so you will be best to copy your star trail files into a new folder on your computer’s hard drive.
I often disregard the first few files and select as many as I want to create a trail however long I think looks best. If dawn came and washed the sky out towards the end, then I can leave those last few files out of the final trail.
The Raw method undoubtedly takes far longer so it’s best to save the processing for a time when you can leave the computer to do it’s thing for a while, but I am confident you will notice a significant improvement over your star trails using this method.
After some rather time consuming initial fails and some jubilations you’ll be well prepared with the knowledge, and most importantly, the confidence to shoot star trails for several hours knowing you will end up with a great shot once you’ve finally got home and processed it… So get out there and find some locations, push your boundaries, conquer your fears and own the night.
Good luck, happy trailing and try not to swear at the planes too much.