Saturday, 21 December 2013

Star Trail Tutorial

The photo given below was taken in the Moroccan Atlas mountains while on a hiking trip. The total exposure time is 56 minutes, the photo consists of 28 2-minute images stacked using startrails.exe.

Star Trail Tutorial
Star Trail Tutorial

The map position is very approximate.

Here's my tutorial:

To capture the movement of the stars at night, you'll need to have a very, very long exposure, 5 minutes as a minimum, but usually more like an hour. To do so, you could just produce one ultra-long-exposure frame using your camera's bulb mode, but there are several problems with that. First of all, if any problem occurs during this time (ie your camera shuts down, the memory card has a write issue) you will lose all the information, which can be a tremendous annoyance if you had a three-hour exposure underway. In addition, if your picture has any other elements that might be brighter than the stars, such as the tent in my shot, (which it should have to make it an interesting image) these will be very; very overexposed if you use a shutter speed such as 60 minutes. Therefore, almost everyone doing star trail pictures uses the so-called stacking method, in which a number of images are taken, and then stacked to simulate a very long exposure.

Below, a step-by-step guide:

Startrail Tutorial
Startrail Tutorial  - This photo was taken in the  Moroccan Atlas
 mountains while on a hiking trip. The total exposure time is 39 minutes,
 the photo consists of 13 3-minute images stacked using startrails.exe.

1. Set your camera up on a very sturdy tripod, and frame your composition. If possible, frame your shot before nightfall, since when the stars appear it will be very difficult to compose because of the lack of light.

2. Decide how long you want your total exposure to be. Keep in mind that the stars will be moving along concentric circles centered on the northern star. Therefore, if you point to the north, you will need a much longer exposure for your trails to be a of a given length, and conversely, it you will need a shorter exposure as you point more to the south.

3. Now, you will divide this total exposure time you chose into many shorter exposures. I like to use 2 minutes, but use anything that does not overexpose any parts of the frame, while trying to stay under 8 minutes or so. So say you wanted a total exposure time of 56 minutes, which would be 28 2 minute exposures. You will achieve this by setting your camera to the bulb setting in manual mode and then connecting an intervalometer (50$ online). The intervalometer will send the signal to your camera to open and close the shutter every two minutes. The only reasons cameras are not able to do this natively, as well as many other features, is because manufacturers purposefully limit their functionality. So set your intervalometer to the desired exposure time and number of frames, and set the interval between frames to 0. (in my case: exposure time:2 min; number of shots: 28)

4. Set the focus to infinity manually and start the intervalometer. Wait until all the shots are taken.

5. Now the stacking: you will need to use a program that stacks the images by choosing the brightest pixel when there is a conflict. This will make sure the little pieces of star trails are all combined in the final image. I recommend startrails.exe for windows, but you can just google star trails stacking and you’ll find lots.

Have fun: Thomas Sittler

Related Reading

  1. How to Photograph the Sun
  2. How to Photograph the Milky Way
  3. How to Photograph Rain Drops
  4. 22 Tips for Photographing Stunning Seascapes
  5. Forest Photography Tips