I have wanted to photograph star trails, but we live in an area with frequent clouds and significant light pollution. However, last week we were in Meteora, Greece (there will be more about that in other posts), staying in a room with a balcony which was directly adjacent to the massive rock pillars that make this area a tourist attraction. After dark the first night, we saw the stars and they were magnificent. This was clearly a photographic opportunity.
We selected Canon 100D cameras for this trip because of their small size and weight. I mounted one on a travel tripod and attached a 10-18mm EF-S wide angle lens to make some test shots. It was totally dark, so autofocus wouldn’t work. It was so dark, in fact, that it was not possible to focus through the viewfinder. Taking a good photo would involve trial and error.
I wanted to take my photograph at ISO 100 to minimize sensor noise and to make as long an exposure as was practical to accentuate the star trails. The camera was put in manual mode with the ISO at 12800 to find feasible exposure times and apertures. Even though the sensor noise at this ISO would render the photos unusable, test shots taken at this ISO allow equivalent exposures at ISO 100 (the best on my camera) to be computed.
A second of exposure time at ISO 12800 is the same as 128 seconds of exposure time at ISO 100. Since the Canon 100D has a relatively small battery, I decided to limit the final exposure time to one hour, which meant the ISO 12800 exposure needed to be around 30 seconds. The exposure time on the camera was set to 30 seconds and a series of test shots was made at varying apertures. Using the display on the back of the camera to evaluate shots, I decided that f/5 gave me the best results. (I actually would have preferred at least f/8 but that would require me to take a longer shot or increase my ISO and I didn’t want to do either.)
Having determined the exposure parameters, the next problem was focusing the camera. I wanted the rock pillars to be in sharp focus to give a clean edge for the star trails. However, since it was pitch black except for the starlight, it was impossible to focus. An attempt to illuminate the rock pillars with a flashlight — a trick which sometimes works — failed because the pillars were too far away for sufficient illumination.
Since we had the room for one more night, we waited for daylight and carefully focused the camera on one of the pillars. To keep this setting, I taped the focus ring in place with gaffer’s tape (no sticky residue when it is removed) to keep the focus from changing. That night, the camera was set up in the same spot and an intervalometer was used to control the exposure time. The photograph shown here was the result.
Settings summary: Canon 100D, f/5, ISO 100, 3540 seconds, 10mm focal length