Must Be Art Weblog

The Moon is dark during an eclipse. The Moon is small. And the Moon is moving. This is a bad combination.

A small subject means a long focal length lens. I don’t currently own any supertelephoto lenses, which tend to be big, heavy, and expensive. My longest lens is a 70-200 f/2.8 zoom, with a 2X teleconverter. That makes a 140-400 f/5.6. Long enough to show the half-degree-wide Moon in context with some landscape, but slow.

Dark subject + slow lens = long exposure

Long exposure + moving subject = blur

The really dumb part of this story is that I had taken the trouble to calculate the longest exposure that would result in minimal blur. I had even posted my results on a web forum. The answer is that shutter speeds have to be faster than about 1/4 second. But I did this calculation five or six weeks before the eclipse, and then forgot the answer. By the time I was out in the field trying to photograph the eclipse, I mis-remembered the answer as 8 seconds.

With a digital camera, getting a reasonable exposure is never a big mystery. You just look at the histogram display and adjust the exposure until it shows something usable. Using this procedure, I ended up with exposures ranging from 6 to 30 seconds. Unfortunately this resulted in so much motion blur that the resulting images are useless.