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Trailing the Night Sky

Star Trails

I’ve always been fascinated with star trail photography. Having the ability to capture the movement of the stars helps us to remind that everything around us is relative. Another somber reminder is that the light we capture from our sky is a snapshot from millions of years in the past. Many of the stars in our night sky pictures no longer exist. In one second, light travels about the length of the circumference of Earth six times! When we look at the Sun setting on the horizon, we are actually looking at the sun eight minutes into the past, meaning that the sun has actually already set.

Capturing images of the night sky is the closest thing to time travel we will ever experience withing our short lifetime.

There are two methods to capturing star trails: Shutter dragging and image stacking.

Shutter dragging is the method of setting the exposure for long periods of time – usually by setting your camera to bulb and exposing the image from 30 seconds or longer. A long exposure will produce noise (or grain) caused by the camera sensor as it becomes hot. Conversely, on cold winter days you will notice less noise from long exposures.

So how do we combat noise from extra long exposures if we want to capture a long star trail?

Image stacking is the method of taking several photos and merging them together to produce the illusion of one long exposure.

In this tutorial, you will learn how to create star trails using the image stacking method.

You will need:

  • camera
  • tripod
  • intervalometer
  • a clear night sky

An intervalometer is a device that triggers the camera’s shutter within set intervals. This prevents you from having to touch the camera to trigger the shutter button which may cause your exposures to be misaligned. Some cameras may have an intervalometer built in. An alternative is to use a mobile intervalometer mobile app that is compatible with your camera. I shoot with a Canon 6D that has a WIFI broadcast that I use with an app (qDSLR Dashboard) on my phone to wirelessly trigger the shutter.

It is recommended to use a wide angle lens – preferably with a very low f-stop. The settings I used for all exposures are set to 25s, f/1.4, ISO 100. These settings allowed me to get a good exposure of the foreground while still getting a clear shot of the stars. Your setting may be different depending on your lens and desired foreground exposure.

In order to get a decent trail of the stars, you will need a least 750 seconds of exposure. 25 seconds a frame times 30 exposures will get us a good 750 second merged exposure.

After you have taken all of your exposures, you will need to import them into a photo editing suite such as Photoshop or GIMP. Load each frame into the same file as layers.

For each layer, you will need to set the layer mode to “lighten”.

Finally, merge all layers.

It’s that simple! Below is the result:

Udall Star Trail

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