Photographing the night sky can be extremely interesting. Though a bit challenging technically, if done following the correct technique, it can yield immensely beautiful results. The world of astronomical photography is a magical, surreal experience. This involves constellation photography, Milky Way photography, computer assisted photography of celestial bodies and the most interesting of all, Star Trail Photography. This article will explain to the reader how to create a star trail photograph. It is not as easy as it reads, at least for one trying it out for the first time. At the same time, it is not as difficult as rocket science!
I owe a special acknowledgement for the technical expertise shared by my good friend Mr. Abhishek Bawkar, who was the first man to instil and develop a huge interest in me about star trail photography and there start my journey. Deserts, plateaus, beaches, valleys, hill tops, forests. the charm of doing star trail experiments in unknown remote terrains and the tinge of unpredictability of the final result every time you do it, is what makes it even more thrilling.
If you are planning for star trail photography outdoors, somewhere in the outskirts of your city limits, you need to first plan the calendar day.
You need to choose to do your star trail photography on a moonless night. So do some research in finding out which is the next moonless night which matches your availability. Most of the moon-set calendars also give you a chart to understand what would be the strength of moonlight on that night if it is not absolutely moonless.
Second is the location. You must do a little homework to find out a location which is away from the maddening city crowd, as far away as possible from where you live. Find a place which has minimum light sources (if possible none) till the horizon.
Gadgets are essential. It is important to carry a Digital SLR (preferably with a wide-angle lens), a sturdy tripod, and a remote shutter release (inexpensive ones are available even at Rs 400).
I would strongly recommend a remote shutter release with a locking mechanism. If you don’t have a wide-angle lens, you may miss the fun but you could still get decent photographs at 18 mm of your kit lens (DX lens, equivalent to around 28mm in the 35mm format). Plan your trip in such a way that you reach the location around sunset time. Ensure that the location you choose is safe enough.
First of all you must try to identify the Pole Star. The Pole Star or the Polaris as it is also called, is situated exactly above the North Pole of the earth and stays there all the time. Since it is in line with the earth’s rotational axis, there is no relative movement of earth and the Pole Star. All other stars appear to move from east to west as the earth rotates around its axis but the Pole Star remains in the same position. This is the principle behind those wonderful star trail images.
Identifying the Pole Star can be done based on two distinct constellations. One is the Great Bear, which looks like a pan with a handle. This constellation is also known as the Big Dipper. The end two stars of the Great Bear are the pointers and when extended along a virtual line, should meet the Pole Star. The other constellation looks like a ‘W’, called Cassiopia. The Pole Star is situated upwards from the top of the ‘W’. A perpendicular line drawn from the 4th arm of the ‘W’ meets exactly at the Pole Star. These days you have a lot of applications in your mobile phone which show the night sky very beautifully. The only challenge you face is when you choose a location which is far off from the city and there is a diminished connectivity of your mobile network. It is therefore important for you to know how to identify the Polaris based on the above mentioned two constellations. There are two different methods to do Star Trail Photography. One school of thought says, on a starry night, after mounting the camera on a very sturdy tripod, you should keep the shutter open for almost an hour in Bulb mode so that the stars create a trail as the earth rotates on its own axis.
The second school of thought advises us to take multiple frames, as many as 100 or 150 or even more, each clicked keeping shutter open for 20 — 30 seconds duration. I prefer the second method.
Once you determine the position of the Pole Star, put your camera on your tripod facing the North Pole. Attach the wired remote shutter release. I suggest you keep your camera in manual exposure mode and in manual focus.
Now compose your frame. Include a small portion of the foreground, and the maximum of the sky. Use the widest possible focal length of your wide-angle zoom lens.To focus, point the camera at a bright star or anything far away. In case you find it difficult to focus manually, you can keep the camera in autofocus mode and try to focus on some bright star or an illuminated object far away. Once it is focussed, switch from autofocus to manual focus. Ensure that you do not touch the set-up, else focus will get disturbed. If you are facing the Pole Star, you will get circles in the final output and if you are facing slightly away from the North Pole or towards east or west, you will get arcs in your final image.
Set your ISO value to approximately 400 — 600. You may have to experiment a little with this. Switch off your long exposure noise reduction. Keep shutter speed at 20 seconds or 30 seconds. Open up your aperture to as much as your lens allows. Keep the shutter in a continuous shooting mode (burst mode).
It is good to check after taking a few trial shots. Once you are satisfied with the exposure and composition, leave the setup and you are now ready to go. If you click the remote and lock it, the shutter being in the continuous shooting mode, will remain open for 20 seconds (if you have opted for 20 second exposures) and after every 20 seconds it will close and open for the next 20 seconds exposure. This will keep happening as long as the remote lock is on. You can relax; your setup is completely a walk-away system now.
If you allow this process to go on for almost an hour, you will get approximately 120 frames if you had kept the shutter speed at 30 seconds; 180 frames if shutter speed was 20 seconds. That’s quite a few to process! Shoot in JPEG.
Now once you have some hundred or more JPEG images, it’s time to stack them up. There are various free software available on the Internet. Once such is Star Trail.exe, which I use for processing my images. It is fairly simple to operate. It will stack all the images and will create a wonderful star trail image for you.
Pack your gear, choose a moonless night and walk out to a remote place far away from the city. You may find me there shooting Star Trails!