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The Making of Star Trails over Old Faithful

Updated: Feb 14, 2021

Star trails over Old Faithful, Yellowstone National Park, Wyoming
Star trails over Old Faithful, Yellowstone National Park, Wyoming

I began planning my image Star Trails over Old Faithful about five months in advance. First, I booked four nights at the Old Faithful Snow Lodge during the period surrounding the February 2016 full moon. Next, I began solving the shoot’s technical challenges. The first was exposure. I wanted to capture the geyser at its full height, lit only by moonlight. Too short an exposure, and the geyser would be under-exposed. Too long, and the geyser would only be at full height for a fraction of the exposure time. The National Park Service Yellowstone website said that a typical Old Faithful eruption lasted from 1 ½ to 5 minutes – a rather broad range. With eruptions occurring only every hour and a half, an exposure strategy of guess-and-check sounded very inefficient. Then I remembered that I had snapped a few frames of an Old Faithful eruption during a brief family vacation the previous summer. By looking at the time stamps on the photos, I was able to determine that Old Faithful’s peak height lasted only 10 seconds or so.

That gave me an exposure time; what about the aperture? I wanted to keep the ISO to a minimum to keep noise under control. That dictated an aperture of f/2.8, the widest aperture on my Canon 16-35mm lens. The final parameter was ISO. I knew that the geyser would be white, as would the snow surrounding the geyser. That meant that I could shoot test frames before the eruption to determine the correct ISO to properly expose snow at 10 seconds, f/2.8, and use the same settings for the eruption. Testing once I was on location showed that an ISO of 1250 would give me correctly exposed snow under a full moon. I confirmed that exposure for the geyser with test shots taken during a partly cloudy night when it was impossible to shoot satisfying star trails.

My normal approach to shooting star trails is to use an exposure of four minutes, f/4, ISO 200. Using that approach for Star Trails over Old Faithful posed a problem, however. An exposure of four minutes would probably turn the geyser into an amorphous blob of steam, which meant I would have to shoot the geyser and star trails separately, then combine them in Photoshop in a believable way – a difficult task. I decided that a better approach would be to shoot back-to-b