Three Exposures Lunar Eclipse

Winter 1996–1997. I was on sabbatical at the University of Michigan, Ann Arbor, and the Hale–Bopp comet was hiding behind an everlasting blanket of winter cloud. It was a typical Michigan snowy winter—freezing cold, especially if your experience of winter is limited to Israel and Arizona. I was frustrated at not being able to see Hale–Bopp, so you can imagine how I felt when I heard there was going to be a total lunar eclipse just above Michigan’s clouds on March 24.

On rare occasions, miracles happen. Early that night the clouds suddenly cleared for the first time in months, revealing a beautiful starry sky, an amazing view of Hale–Bopp, and a full moon. Excited, I took my camera out into the snow, mounted it on a tripod, and set out to photograph the lunar eclipse. At the time I was shooting exclusively color slides. My longest lens was a 200 mm, which is pretty boring for moon shots and leaves no real option for a scenic view. There would be plenty of great images of that eclipse—none of them would be mine. It was the kind of healthy frustration that makes me creative, and it fell on fertile ground: at that time I was experimenting quite a bit with long-exposure photography while moving my camera—either panning or “painting”—as well as with multiple exposures.

However, before even thinking about being creative, I had to solve a purely technical dilemma: how could I meter the light? I had no prior experience photographing the moon at night that I could remember, so I could only make a rough estimate. That is not good enough when you shoot slides. Luckily, there was a street lamp nearby with almost the exact color of the moon. All I needed was to expose for that color, and I knew exactly how to do that using the camera’s spot-metering mode.

Multiple exposures

I shot three or four frames, and I got bored. Then I decided, with freezing hands, to plan a careful three-exposure shot: placing the moon in two corners of the slide, and “painting” a trajectory line with the third exposure. I took the first two shots on the tripod, using a wide aperture, which gave me the fastest corresponding shutter speed I could use for that light in order to avoid vibrations. Then I changed the shutter speed to half a second, which would allow a handheld “painting” exposure. I kept a relatively wide aperture, because the moon’s exposure time at each point along the trajectory would be much shorter than half a second.

The importance of choosing the aperture precisely is shown in the photograph by the fact that the shaded area of the moon is hardly noticeable along the trajectory line: it did not stay long enough at each point to have an impact on the emulsion. A wider aperture would have overexposed the trajectory line made by the illuminated part of the moon.

I intended to paint a half-circle trajectory that began below the moon on the left and ended below the moon on the right. I rehearsed four or five times to make sure I stayed within the boundaries I had planned, knowing that once I pressed the shutter I would effectively be working blind. Then I made the third exposure and hurried back to my safe, warm home.

Another technical note on multiple exposures

Digital cameras that offer multiple exposure usually give a choice between two modes: Average and Additive. Average calculates a per-pixel average across all exposures, most likely by averaging RGB values. Additive more closely simulates multiple exposures on film: pixel values from the different exposures are added together.

In the film days, if I wanted to give equal weight to two exposures while maintaining the intended amount of light on the emulsion, I had to halve the light (i.e., reduce the exposure) in each. On a digital camera, using Additive is the only way to shoot a scene like this; otherwise the moon would be averaged down with the black background of the other exposures and—in a three-exposure shot—would end up with only a third of its intended exposure. In addition, since the background is pitch black, the exposure of the subject should be kept at full value in each exposure on both film and digital, unless the subject is expected to overlap across exposures.

The original slide looked like this:

The result was much better than I had expected, and I preferred the wavy trajectory line over the smooth, precise half-circle that I knew I would never be able to produce. Had the trajectory touched one of the moons—or even come closer than it did to the moon on the right—the image would have been ruined.

Black and White

Years later I decided that I preferred a black-and-white version of this photograph, because it gave it a cleaner look—almost like a precious silver gem. To create the black-and-white version, I simply used Photoshop’s Black & White adjustment tool, with a few slider moves to keep smooth black–gray–white transitions. Finally, I applied sharpening only locally, in some areas of the photograph, to avoid adding noise in others.