POTD: Earthshine

Mojave National Preserve, California

The earthshine (the sunlight reflected from the earth’s surface that illuminates part of the moon not directly lighted by the sun) during the crescent moon was quite visible when we were out on the Mojave Desert last month. It looked great so I thought it worth trying to capture it with my camera. This is an o.k. image but how I got it was pretty much a textbook example of how not to do it.

With the human eye (aided by binoculars or a long telephoto lens of course) it’s easy to see both the craters on the sunlit part of the moon as well as some of the detail on the moon’s night side which is much less brightly lit by the reflected light from the earth. But a single exposure with a camera will generally either result in the sunlight part of the moon being way overexposed or the earthlit part being way underexposed. There is no real middle ground for the exposure settings that will give a decent single result.

To address this issue is pretty easy if you use the kinds of advanced camera and computer tools available to the modern photographer. First of course you should really shoot with a tripod. I have two nice tripods, both safely stashed at home in Montana, so I was shooting handheld. Secondly, you should take advantage of the high dynamic range (HDR) settings available on many cameras and/or the appropriate computer software. But that approach only works well if you’re using a tripod.

So I did it the old fashioned kludgy way–I took one image exposed for the sunlit part of the moon and one exposed for the earthshine part and laboriously combined them in Photoshop. I say laborious because for a number of reasons it was much more difficult to get a decent looking image than I thought it would be. I easily spent a couple hours tweaking what I had to get what you see here. It’s not perfect but gives a good representation of what I could see with my eye looking through my telephoto camera lens. And it was a good lesson in being better prepared in the field next time!

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