While star and night-time photography is nothing new, recent advances in digital camera technology has really made this genre a lot easier. One unfortunate fact in night photography is that one needs to be in an area or location where light pollution is low, and the lower it is, the better the results will be.
Among photographers, there are often arguments about the use (or otherwise) of manual mode. Some seem to believe that you are not a real photographer unless you control each function of the camera, while others believe that they pay good money for all aspects of the camera, including the built-in light meter, processor and programming that make all the automatic and semi-automatic modes work. However, at present, experimenting with night-time photography requires the use of manual mode, as no current built-in light meters are sensitive enough to handle the low levels of light inherent in this type of photography.
Herein probably lies the biggest deterrent for newbies, but just like in most other forms of photography, the ability to review your images almost immediately is one of the biggest advantages of digital technology, and effectively makes this barrier much easier to overcome.
The genre may be roughly broken into a number of categories:
- Astro-landscapes (also known as starscapes).
- Star trials.
- Northern lights/St. Elmo’s Fire/Aurora Borealis.
- Time-lapse photography.
Let us define each category briefly, and have a quick look at what equipment will be needed:
The basic idea is to capture a landscape or fixed item of interest, with a spread of stars in the background.
This is perhaps the simplest category, requiring the least in terms of specialized equipment. Really all you need is a digital camera, a wide-angle lens and a tripod. A cable release, a small torch, a rag or two, something to cover the viewfinder and, if you are in a cold climate, some chemical warmers may also come in handy. However, because you need to gather a lot of light in a short period of time, it can be quite challenging to the camera and lens combination. The wider the angle of the lens and the faster it is in terms of maximum aperture, and also the better your camera is at high ISO’s, the easier it is to get good results, but there are post-processing tricks to get around less than ideal equipment.
- Star trials:
There are basically two methods to create star-trials. The first is to take a single very long exposure, capturing the earth’s rotation relative to the stars, and the second is to take a whole series of shorter exposures, similar to astro-landscapes, and then stack them digitally atop each other during post-processing. Equipment requirements are similar to the equipment needed for astro-landscapes. However, if one wants to use the stacking method, a cable release or intervalometer will be required, while if the single-exposure method is followed the requirements on the camera’s ability at high ISO’s and the lens’ speed becomes less important. On the other hand, the single-exposure method is a bit more fraught with the possibility of wasted effort, for reasons that will become clear in a minute.
- Northern lights:
Firstly, one obviously needs to do this near the poles, where the Northern lights are visible. Other than that, equipment is very similar to that needed for astro-landscapes, with the addition of warm clothing and the understanding that chemical warmers become almost obligatory. You may also need some extra batteries, as the batteries’ capacity are significantly reduced in very cold conditions.
Time-lapse photography is basically taking a series of still photos at frequent intervals and then editing them into a video format. It is in no way limited to night-time only, but those that encompass the time period when day turns into night and vice versa really add an extra dimension. Equipment will vary depending on the subject matter, but typically the same equipment as for the categories above will do a great job for simpler videos, except that one definitely needs an intervalometer. Note that the fancier Nikon cameras (from D7000 upwards) have one built in. Additional equipment that will come in handy sooner or later are a smartphone or tablet loaded with an application such as DSLR Dashboard, a cable or WiFi to connect that to the camera, and a slider or dolly system.
Effectively this is the process of attaching an imaging device to a telescope. This fascinating hobby unfortunately requires some fairly serious equipment. Firstly a telescope and an adaptor to bolt a camera onto it, but also either a “barn door mount” or an “equatorial mount”. These devices allow you to follow the stars or galaxies you are aiming at, with various degrees of accuracy dependent on the complexity of the equipment and the trouble taken in the calibration thereof.
Let’s take a closer look at what you will need. As mentioned before, the basic kit for astro-landscapes is a good starting point for all the other categories except digi-scoping.
Firstly, a good, steady tripod. Ideally a sturdy but lightweight one that can be erected with the legs wide open to get the camera low to the ground. Because you will not be using a long, heavy lens, you don’t need one with a very high load capacity, but because you will be taking pretty long exposures, it needs to be sturdy, but remember that you might need to walk a ways to find that stunning composition.
Next up, the camera. The ideal is a relatively recent full-frame, (or larger), camera with a relatively low pixel count. The Sony A7s is perhaps the best camera for the job available now, but all the current full-frame cameras from the major manufacturers will do a very good job, and acceptable results can be achieved with any of the current 1.5x and 1.6x crop-sensor cameras assuming you are prepared to put in a little bit of extra effort during post processing.
The lens is perhaps the heart of any imaging system. The shorter the focal length, the longer the exposure can be before the stars start “streaking”. Remembering that the primary obstacle is gathering enough light, a shorter lens is generally better. However, because slightly longer lenses are available with faster apertures, the focal length is not the be-all and end-all, but generally the ideal is something between an effective 14mm to 35mm, with the fastest aperture you can find. Perhaps the most popular lens for full-frame cameras for this type of work is the Nikkor 14-24mm f2.8, (to the extent that even some Canon photographers use it with a suitable adapter). Personally I am very impressed with my Tamron 15-30mm f2.8. Optically this is apparently tough competition for the legendary Nikkor, especially short and wide open.
However, the lens need not be a zoom, and nor does it need auto-focus. For full-framers on a budget, the Samyang/Rokinon/Bower, (all the same), 14mm f2.8 is quite popular, although one apparently has to be careful as their quality control is said not always to be stellar. A 20mm f1.8 is also great and the various 24mm f1.4 lenses on the market also make excellent choices. Personally I like the really wide angles, as you can get more of the milky way into a single photograph, but better results can arguably be achieved by using one of the longer ultra-fast lenses and pasting several photos together in a panorama.
Obviously, the chosen lens should ideally be pretty sharp, preferably right up to the corners, but coma performance is also important, (coma shows itself as slight “streaking” of the stars in the corners of the frame).
If you are using a crop-frame camera, head and shoulders the best lens to use at the moment is the Tokina 11-16mm f2.8
Usually, either a cable release or an intervalometer will be very useful. If the camera does not have a built-in intervalometer, perhaps it’s better to just buy an intervalometer and get it over with. If you are using an external intervalometer, make sure you have some spare batteries handy.
You will also find a torch of some kind virtually indispensable. It need however not be large or powerful. If your camera has a strap, take some rubber bands to tie it down with, and if you are shooting during the pre-dawn hours a rag rubber-banded over the camera and lens is useful for keeping your camera dry from dew. It is also recommended to close the viewfinder during long exposures to prevent light entering the camera from the back from making it onto the image sensor. Some cameras have a built-in shutter while others come supplied with a clip-on plastic one, but failing either, a cloth or some sticky tape can be used.
So how does one go about it? Start by setting up the camera, ideally while it is still light. Set the quality to RAW and the white balance either to dailight or to a set temperature. Most people seem to prefer a temperature of around 3500K. Place the camera on Manual mode and if you are planning to use autofocus, set it to single-point. If you are going to focus manually, just set it up now. Depending on what type of result you are going for, you want a drive mode of either continuous or self-timer. Make sure you have enough room on the memory card/s and enough juice in the battery.
The hardest part is getting a nice composition when it’s dark. And the key is not to. Find your composition while it’s still light enough to see. However, then you will not be able to see the milky way yet. If you are in the southern hemisphere, the problem is not too bad though, because the milky way will have its’ bottom end pretty close to due south, and that is also where you normally want to be pointing for a star trail as well (in the northern hemisphere, you want to be pointing north) as this is what gives you the circles. Unless you specifically want to put the turning point at a specific location, you don’t normally have to be too accurate though, since with a wide-angle lens you are covering a relatively wide sweep of sky. Also, the Southern Cross is generally the first constellation to become visible, while there is still enough light to change the composition if you so desire.
A tip here: if you are in a less-than-ideal area in terms of light pollution, find yourself a hole or depression.
Focus is the next thorn. Again, fortunately we are talking about wide-angle lenses, which are fairly forgiving in this regard. A lot of people recommend setting the lens to the so-called hyperfocal distance and taping the focus ring down, while others recommend doing the same but at infinity. Personally I like switching to live view, zooming in on one of the brightest stars and focusing as precisely as possible on that. The really OCD guys take separate exposures of the foreground and the stars, focused individually. If you want to focus on the foreground, you will either need to do this while it is still light, or shine a torch at it, which should provide enough light for the AF system to work or for live-view manual focusing. Note that once focus is acquired if not before, you need to switch the AF system of to ensure that the camera does not try to re-focus for the next shot. Some guys tape the focus ring down to ensure that the focus doesn’t shift.
After this, the most challenging part is getting the exposure right. Let’s start with the basics: there are three factors determining overall exposure, being exposure time, lens aperture and ISO. These are adjusted to suit the overall light level present in the scene you want to photograph. There are a number of units used for expressing the level of light present, but the one used in photography is called Ev or Exposure Value, (also known as “stops”). The camera’s built-in light meter measures this, and either makes adjustments to the above three factors automatically, (in Automatic mode), or adjusts one or more of the factors, or even just gives the photographer guidance with regard to the suitability of the values he or she has chosen. The manufacturers of modern cameras do everything in their power to make this process as easy as possible, and one of the simplest ways they do this is by ensuring that each increment of adjustment has the same effect on the exposure value. Normally, this is one third of an Ev. And one Ev, (or one stop), adjustment either doubles or halves the amount of light captured.
However, the light meter is of almost no use for the photography we are considering here, because the light meters in modern cameras are only effective down to about -2 or -3Ev, but to capture a reasonable amount of stars, we need to be capturing at least -7Ev.
So how do we determine the correct exposure? My method is to start with a basic exposure, similar to what one would need to capture an astro-landscape photo. I recommend this because it is the fastest and easiest way to get a base to start adjusting from that is suitable for virtually all the categories, and yet is easy to remember.
Start with the aperture. Simple: open it as wide as it will go. Secondly, the exposure. There is a rule of thumb that reads that the exposure is calculated by dividing 500 by the effective focal length. This varies somewhat with the camera’s resolution and the exact piece of the sky you point the lens at, but it’s good enough to start off with. So assuming you have a 14mm lens, the first try at exposure would be 500/14 = 35 seconds. Set the camera to the closest exposure to this, which would generally be 30 seconds. Lastly, set the ISO to the highest value you are prepared to deal with, or calculate the ISO for an Ev of -7, (there are a number of photography apps and programs available that can do this, and you only need to do it once, since the camera and lens remains the same). As a rough guide, a 30-second exposure at f2.8 needs at least about 3200 ISO. Once it’s nice and dark, take a test shot and evaluate the results. Note that because it is dark, a correctly exposed photo may look too bright on the LCD. It is important to evaluate the exposure by looking at the histogram. Also zoom in close in the corners, and check for signs of the stars streaking. If the stars are streaking, you need to reduce the exposure a couple of clicks, and of course increase the ISO by the same number of clicks. However, be careful to note the direction. Coma looks very much like streaking, except that streaking will be in a predictable direction, (by keeping in mind the earth’s rotation and the direction the camera is pointing), while coma would probably be in more random directions. If you have changed the exposure but the “streaks” are still the same after the next test exposure, then it is caused by coma, in which case you can try taking the exposure back up to the previous setting and closing down the aperture a little instead.
Foreground illumination is a matter of personal taste, and also a matter of choosing the conditions carefully. The immediate foreground can be illuminated by a variety of means, such as shining a torch into the palm of your hand and reflecting it onto the area in front of the camera, or firing a very strongly diffused speedlight. However, this can only illuminate the immediate foreground. If you want to illuminate the whole area in front of the camera, there are a number of methods one can try. These range from waiting for the moon to start rising, or shooting under a very weak moon, to taking a much longer exposure from which you erase the stars and then stack with one or more photos of the stars. Note that for a series of photos to be used for a star trial, only one photo needs to have the foreground lit, while if you are taking a series of photos to be used to make a time-trial video, you will need to use natural illumination or provide similar illumination for the whole series. Once again, use the histogram and highlights warning to get the foreground illumination right.
If you are taking an astro-landscape only, then the fun part is done.
If you want to carry on to do a star trial, you now have three options. If you are happy with your camera’s noise performance at the ISO levels you have taken the above photos at, you could just carry on taking photos on continuous drive mode. Keep in mind that the stacking procedure will tend to cancel out a lot of noise. Just lock the remote or cable release’s button down. On most Nikons, the camera will take a maximum of 100 photos in a single string. If this is not enough, you need to be ready to release and press again. I don’t know if other camera brands have a similar restriction. If not, then you could either increase the exposure time and reduce the ISO by the same number of stops, (for which you may need an intervalometer as your camera probably doesn’t have set exposures of longer than 30 seconds), or you could try a single long exposure. Again, you will be increasing the exposure and reducing the ISO and possibly also the aperture to the extent that you get the length of trails you want. The biggest disadvantages of the single-exposure method is that a single exposure will take between one and a half and several hours, and if the exposure is out or somebody inadvertently shines a light on the subject during this period, there is no recovery except to start over. In a stacked image, one can easily just delete the affected images, and you can test the exposure more accurately beforehand as described. For either method, calculating the exposure time is done by doubling the exposure time for each three clicks you reduce the ISO or the aperture.
The other advantage of using the stacking method is that you can use the same string of photos to create an astro-landscape, a startrail and a short time-lapse video.
Although I have no personal experience here, I understand that the method above can also be used as the basis for capturing the northern lights, although one would usually be operating at a somewhat lower shutter speed and total exposure value to retain some shape in the lights, as the Aurora Borealis moves around quite quickly.
If you want to take a series of photos to make a time-lapse video from, keep in mind that your camera needs to be in landscape orientation. If your intention is to capture the transition of day to night or night to day, you will need to adjust the exposure during the series. In this case, it is necessary to use an intervalometer, (either built-in or external), and to set the gap between exposures to a value a few seconds longer than the longest exposure you are expecting. The actual adjustments can be done manually, (in which case you need to be present all the time, and you need a very sturdy tripod), or it can be automated by applications such as “DSLR Dashboard” on a smart-phone or tablet plugged in to your camera or connected via WiFi. This application downloads the JPEG preview of the previous photograph, evaluates the histogram and adjusts exposure on this basis. The latest versions can adjust all three exposure variables within limits set up by the user, and can do so very smoothly for flicker-free results.
Lastly, let’s look at post-processing. Keep in mind that some techniques here may determine the quantity and types of photos you take. Also, the more basic your camera and the larger your output, the more effort you will be putting into the post processing.
The most challenging category to post-process is Astro-landscape. The reason is that in either star-trials or time-lapse videos, noise is much less obvious. In star-trials, you will either have a very long exposure taken at relatively low ISO’s to work with, or the act of stacking a bunch of photos will tend to cancel out a lot of the noise, while in video, resolution is much lower and thus down-sampling takes care of a lot of the noise.
If you have a good full-frame camera and wide-angle lens combination, you can get to fairly large print sizes using just basic processing of a single photograph in a program such as Adobe Lightroom. If this is not good enough, there are a number of techniques that can be used to improve the results. Firstly, there are a number of plug-in programs that may be able to do a better job of noise reduction. Secondly, one can take a short series of photos and copy them into two sets. After importing them into Photoshop, delete the stars from one set and the foreground from the other set. Then two photomerge stacks are created, (one from the photos in each set), and a median de-gausing filter is applied to each. This cancels out most of the noise in each area. Then, the two halves are combined in a single photograph. If this method is to be used, it would be even better if two sets of photos were deliberately taken, one set focused on the stars and one focused on the foreground. The foreground photo could also be a single photo of longer duration at lower ISO, (reducing the need for noise reduction) and higher exposure, (reducing the need for light-painting). Another method is to take a series of photos with a longer, faster-aperture lens at different angles and combine them into a panorama. This effectively increases the resolution of your camera and makes the grain of the noise much smaller for a similar output size. Using either of these longer methods, a very large print of stunning detail and quality can be produced.
For star trials, the method used to take the photos will determine the post processing required. If a single long exposure was taken, it can be processed normally just like any other photo. If a series of photos were taken, my preferred method is to develop the first photo, (if light-painting was done, it must be the “painted” photo), and develop it in a program such as Lightroom. All the adjustments are then copied to all the other photos in the stack, and then export them in a batch to JPEGs. I then have a quick look-through and delete any photos where inadvertent light pollution is present. It hen import them into StarStax, (a freeware photo-stacking program) and process them using one of the program’s set methods.
For time-lapse videos, I recommend the combination of Lightroom and LRTimelapse. LRTimelapse is a program designed to assist in calculating and smoothing out small exposure differences and then creating a video, but the actual adjustments are done in Lightroom. Basically it identifies “keyframes”, being the photos where an exposure change happened, which are then developed according to rules laid down. The program is available either for purchase or as freeware, only difference being that the freeware version limits the user to time-lapse sequences containing not more than 350 frames.
Text and photos courtesy and copyright @Peter Connan
Note: this was due for publication in issue 4 of the Safaritalk Magazine.