The Making of “Immovable”

A summer of learning how to take night sky and Milky Way photos inspired me to think of other ways to expand my skills. One obvious option was to experiment with star trails, arcs inscribed by the stars during a very long exposure. This was a new challenge for a couple of reasons:

• In astrophotography you normally work against the earth’s rotation so that the result is packed with clear detail. Star trails, on the other hand, showcase the earth’s rotation over time.
  
• Leaving the camera alone to take a long sequence of exposures requires its own change in thinking. Will the camera overheat? Do I have to babysit it? How do I know I’m getting good results when I can’t check the screen?

In terms of equipment, my Pentax DSLR has an internal intervalometer, which allows me to tell the camera exactly how many photos to take and how long to wait in between each one. My trusty Rokinon 16mm f/2.0 is great for wide night shots, and I usually put an intensifier filter on it to moderate light pollution.

As for the composition, I already had a shot in mind. On a previous walk along the beach, I’d seen an odd concrete cube nestled in the sand, and it stuck in my mind. I loved how out of context it seemed. What structure did it once belong to? How did it come to rest here? What was its original purpose? It almost looks like it was ejected from an explosion. The mystery of the cube might pair well with the vastness of the night sky.

I started my research with a PhotoPills article that I’d recommend for anyone attempting a star trails photo. Not only does it contain planning tips, but it goes to lengths to help you understand what you’ll be seeing in the sky and why. With a good idea of what my setting should be and how the star trails would look in the frame, one thing remained: scene lighting.

A bright moon is usually the enemy of a crisp, clear night photo, but in my experience it can also give you free lighting on the landscape. The question was how much moonlight I could include without having the sky washed out. On my first attempt, the moon was far too bright, resulting in a blue-tinted sky and fainter stars. A couple weeks later, the moon was out again, but low in the sky as a waning crescent. It was dark enough that I had to take a few foreground shots using a flashlight to paint the subject.

The hollow cube with its large circular openings was perfect for lighting from the inside. A quick stop at Party City and I had a handful of cheap glow sticks to toss in there (it should go without saying that I removed the glow sticks after use).

Results

The first attempt answered some logistical questions, like how much light the glow sticks could emit, how bright the sky was, and how to use the intervalometer. The interval drive mode has some quirks – you set the interval for the length of your exposure plus a second or two to allow the shutter to operate and to keep the camera/sensor from overheating. If you don’t do this, the camera “misses” the exposures that it was unable to start on time. So if you’re taking 15″ exposures, set the interval for 16″. Of course, this introduces a tiny gap as the stars move between shots. I found that, after stacking the images in StarStax, this gap was not exactly smoothed out, but acceptable at most viewing sizes.

Another thing to consider is the length of the interval. Mine was about 40 minutes long, but the final image uses only about 20 minutes worth. It’s up to you how long you want the trails to look, and how you feel that affects your composition.

Your focal length also affects the appearance of the star trails. My 16mm lens captures perhaps too many stars because the field of view is so wide. I need to think of ways to reduce the number of stars – longer focal length, tighter aperture, perhaps. Noise reduction in post-processing did help to eliminate fainter stars and make things easier for StarStaX. I also wonder if it might work to de-focus the sky a bit to get fewer, fatter star trails as opposed to a large number of fine arcs.

My chosen location was sandy. I did my best to stabilize the tripod, but in hindsight it easily could have shifted due to my movements or to those of a passerby. When you pick a location, make sure you can keep the tripod stable for the entire length of the interval.

Capturing star trails was a very different experience than I’m used to. Typically I’m intent on the camera and the scene, analyzing my composition, etc. To leave the camera alone for 45 minutes is very passive by comparison. On the other hand, it lets you truly experience an area by night, watching the sky and listening to the surroundings. I just let my mind wander as the waves crashed on the beach below. I was somehow content doing nothing.

Both excursions out to the cube were valuable learning experiences. My star trails aren’t perfect, but I think they’ll only improve in the future.

Notes