by Trevor Williams.
I will attempt to explain here how to capture stars over a long exposure so that they leave behind a “trail” or light stream. In fact, what are recorded are stationary stars and the rotation of the earth. The images that are created have a unique magic about them that captivate viewers.
A lot of people mention that their love of photography comes from capturing that perfect moment in time. When shooting at night those “moments” become a little longer. When shooting star trails those “moments” turn into hours. Capturing that perfect hour or two in time is what makes shooting star trails so fun for me. When I look at star trails pictures, they remind me that this big rock we live on is spinning out in space. For such amazing looking pictures the technique is really quite simple.
You will need a few things before you head out into the night especially a camera capable of shooting in “bulb” mode. You will also need a cable release and a location far way from any city lights. I usually look for a place with some foreground interest like some trees or old buildings. You should also make sure you are prepared for the environment and weather.
Before we get started, I suggest getting into your car and driving far away from the city. The amount of visible stars will greatly increase the farther away you get from any town. There are a few ways to go about shooting star trails. We will start with the basics that do not change whether one is using a film camera or digital camera. Before setting up the camera on the tripod it is a good idea to set the focus. In the dark, it is not easy to get the AF to lock on to anything.
I suggest trying on one of the brighter stars in the sky and if that does not work set the focus to infinity. It may seem to be the obvious thing to do from the start but not all lenses are perfectly accurate. If you do manage to get your camera to auto-focus be sure to set it to MF or manual focus before starting your exposure or it will star searching again when you start the exposure. Once you have set focus set up the camera on the tripod and compose the shot.
Try not to include any direct light sources, like streetlights, in the shot. One more thing to think about is white balance. I tend to shoot night skies with the white balance set to “tungsten” which gives a nice blue look. Warmer colors tend to give the sky a dirty look. I now suggest doing a test shot which aids in composing your final shot. A 2-3 minute exposure at high ISO and wide aperture is enough to be able to see which direction the stars are moving and allow one to imagine what the final shot will look like.
For shooting options, one could choose to do it all in one shot or shoot multiple shots and “stack” them after using computer software. I personally find that shooting multiple images and stacking them yields much nicer images than those done all in one shot. If you are going to do it all in one shot then your biggest concern should be noise.
To avoid noise, one could use a narrower aperture and a lower ISO speed but these settings will typically not pick up very many stars. If this is the route you are going to take, and I suggest at least trying it, then focus and compose the shot. Set the time value to “bulb”, the aperture to its widest, and with and ISO at 200, try for a 30-minute exposure with a wide aperture of 3.5 – 4.0. If there is too much noise then drop the ISO to 100 and either shorten the exposure time or try a narrower aperture.
If shooting this way is your only option, there is something that you can do to increase the appearance of the length of the trails in the frame that will be limited due to the short exposure time. The actual length of the trails is determined solely by time but the appearance of the trail length is determined by the focal length you are shooting at. For example, stars over a 30-minute exposure would appear much longer in the frame at 50mm than they would at 10mm. If you find that you are limited to shorter exposure time due to noise, or any other factor, try shooting at a longer focal length to increase the appearance of the star trail length in relation to the frame.
Now on to my preferred way of shooting which is multiple shots that will be stacked later using computer software. Shooting this way means one can shoot with a wide aperture and a faster ISO that will pick up many more stars than the previous method. One can do this because noise becomes much less of a factor.
Noise generally increases with time so you only have to worry about 30 seconds that means even at ISO 800 it is not really going to cause a problem. There is even an option to include dark frames, which are frames shot with the lens cap on, so that even the tiny bit of noise from ISO 800 over 30 seconds will be removed. With the higher end DSLR’s and the improvement of sensor noise reduction in recent models means that the ISO can be bumped even higher that will result in even more stars.
You will need to find the balance for your camera. Now with the evil “noise” taken care of the only thing limiting your exposure time is your battery life. For this method it is necessary to use a cable release and it is also important to make sure there is plenty of space on your memory card. To get started, set your focus and compose your shot. Set the aperture to its widest and the ISO to 800. Dial in 30 seconds for the time value and the drive to “continuous shooting” mode which allows for non-stop shooting when the cable release is locked. I suggest doing a test shot first to see if it looks all right. If anything is too bright then dial the ISO down.
Once you have taken the shots you will need to stack them using software. I recommend a freeware program, startrails.exe, available from www.startrails.de. Simply import the pictures, hit the ‘build’ button and wait for it to finish rendering. Don’t forget to save it when it is finished, as the there is no auto-save function built into this software. This is only available for Windows but there are many free actions for Photoshop if you are using a Mac. Simply search “star trail Photoshop action” and you will find what you are looking for.
Single Image
Stacked Image
To complete the shots, an idea is to include a foreground element, like a structure or tree, and light it with a flashlight or flash. I highly recommend testing out how much light is needed before locking that cable release. Too much light will distract from that beautiful star filled sky you are about to create. For foreground lighting use a warm color if you chose to use the recommended “tungsten” white balance.
If you use LED light with such a cold white balance setting as ‘tungsten’, you will find objects in the foreground look very blue. To avoid this, you could apply an amber gel to a flash or use a tungsten light source like a flashlight that has a ‘regular’ light bulb as opposed to an LED bulb. I also suggest doing the foreground lighting at the beginning and again at the end incase one of those is unsuitable for the final shot. You simply exclude those frames from the stack.
If it was done in the middle and a mistake was made leaving those frames unusable it would create a break in the trail that would take away from the shot. A final note for those with experience in night photography, keep in mind that you are now shooting wide open with your ISO bumped to 800 so adjust your lighting techniques to accommodate for that with low power flashes or less lighting time with a flashlight.
All in all, a rather simple technique that yields captivating results.
