My tips on taking star trail photos
06 October 2011
I have been experimenting, and learning a lot, about taking star trail photo's. Star trails look great and are relatively straight forward. Getting a spectacular shot is not really difficult, but there are some essential bits of equipment you need. So, let's explore what is needed for a great star trail photo.
Some Background Info
It helps to understand what causes star trails. While it may appear that the stars move across the night sky we know that is not strictly true. People thought that the earth was the centre of the universe, and that the sun, planets and stars revolved around us. That was, until Copernicus developed the idea that the sun was the centre of our solar system in about 1495. So it may appear that the stars and planets are moving across the night sky, but in reality it is because the earth is revolving. The spinning of the earth is what gives us night and day.
It's like watching a friend who didn't get on the merry-go-round with us, as we go spinning past them. The difference is that the earth is so big we don't feel it spinning. In a star trail photo the light trails record the our movement as the earth spins and we move past the stars fixed in space.
The circular star trails result from pointing the camera towards the Southern Celestial Pole in the Southern Hemisphere and the Northern Celestial Pole in the Northern Hemisphere. These are the end-points of the axis that earth spins on. It is simpler than it sounds, but still amazes me.
You can read more about the photo above in the Gallery section here.
Essential Gear
Camera with no flash, or flash that can be disabled: The first step is to switch off the flash. Our nearest star, besides the sun, is 4.2 light years away. That means it takes nearly 27 months for it's light to reach us. Even if you had an enormously powerful flash, you would have packed up, gone home and forgotten about the photo before the flash reached the star, let alone reflected back to us in 8.4 years time. So a flash is useless.
Camera with manual controls: What you need is to be able to over-ride the automatic settings and choose the ISO, aperture and shutter speed yourself. If you have always used the Auto settings this is the time to break the habit! It is safe and you will feel better for it.
Sturdy Tripod: The camera needs to be perfectly still for the whole shoot. Even the slightest knock or movement will be seen in the final result. You need to be very aware of where the tripod legs are, and you feet in relation to them, to avoid bumps. It's best not to extend the centre column of the tripod as this makes it less stable, especially if there is any wind. Another source of movement can be catching your hand or jacket on any cables attached to the camera. This could include the remote release.
Remote Release: Pushing the shutter down with your finger can introduce vibrations. You could get around this by setting the 2 or 10 second delay on your camera. That is going to get boring and impractical for the number of photo's you will end up taking. It is far more reliable and convenient to use a wired remote shutter release with a timer. These are called intervalometers. They accurately measure intervals of time. Typically you can set these to have a regular time between shots, and have exposures of a consistent length. The other advantage is being able to set how many shots you want, or even to have the camera run until the memory card is full or the battery goes flat.
Ample Storage: You will be taking multiple photo's, so you need room to store them. You can always change memory cards, but that risks creating a gap in your star trails. Normally I don't like huge capacity memory cards. The risk of losing too many shots if one malfunctions is not worth it. However, I do have a large memory card that is used exclusively for star trail shoots.
Plenty of Power: The other component of your gear that could be stretched is the power supply. There are ways to extend the life of your battery, but it may not be enough. You can buy a battery grip, which essentially doubles your power supply. If you are shooting from home you can always get an AC adapter and plug into a powerpoint. If you get more serious you may want to look at using a small 12 volt battery with the output voltage regulated to match your camera. But that's getting into a whole new realm.
Seeing in the Dark: Star trails are taken at night, so you will need to be able to see what you're up to. I mostly use an LED headlamp with several brightness settings and includes a red LED. This is helpful for finding your way around and checking settings without introducing any stray light into the photo's. I also carry a spare LED torch and batteries, just in case.
Getting Out There
You may be one of those fortunate people who lives far from any city or town lights. Most of us need to travel to get away from the light pollution of city centres. On a dark night you can see the glow of cities for miles, and this shows up in long exposures and the multiple exposures of star trails. The impact of light pollution on star photography is diminished contrast in the night sky. All that scattered light from cities means that faint stars are no longer visible. Moonlight has a similar effect. It is similar to looking at a scene as fog rolls in to reduce visibility. So you need to be in a dark region with the least amount of light pollution possible.
Keeping Comfortable: It can get cold so it helps to make sure you have extra layers of clothing. I always make sure to include a windproof jacket as it is surprising how cold even the gentlest of breezes can get after a while. Warm drinks and snacks also help.
Camera Settings
Setting will vary depending on your camera and how it handles noise. That is, the electronic 'fuzz' you get in the dark areas of images, not the nocturnal sounds you may hear. As you increase the ISO so the level of noise increases in your images. It becomes a matter of finding the balance between sensor sensitivity and acceptable noise levels. Higher ISO means shorter exposures, and more photo's to process later. As well as processing images to produce a star trail photo I also use the same images to produce a time-lapse video. So I use a fairly high ISO to enable the video to last more than a couple of seconds. Using a low ISO and shooting with longer exposures does increase the chance of getting 'hot' pixels. These are where a receptor on your camera's sensor overheats and simply records a bright red or blue pixel.
It is helpful to have a short time between photo's, that way the likelihood of gaps appearing in the final image is reduced. This is where the intervalometer is essential. The idea is to have the shutter open for as much of the timeframe you are shooting over as possible.
Results
There is another whole blog needed to talk about processing the images, that's for a later time. A few nights ago I went and took star trail shots even though there was a half moon. That meant more light in the sky, so not ideal. The settings I used were: 1600 ISO, f 2.8, 20mm lens, 20 second exposures with 1 second between them. Over a period of five hours the camera took 650+ photos.
This is the result.
from Rob Packer on Vimeo.
