April 16, 2013

Tutorial - The Moon and the Land


The Moon and the Land

The recent full moon I witnessed over Death Valley and the eastern Sierra was a good teaching moment for me.

We get into habits, some of them dating back decades, and sometimes it takes awhile for those old habits to be challenged and supplanted by new and better ways of doing things.

The brightness difference between the full moon, which is very bright, and the rather dimly lit landscape below, can be a real photographic challenge. Although our eyes and mind rapidly adjust as we glance between the ever so slightly different locations in our gaze, the camera cannot. Timing a day before or day after the actual full moon can give you more light on the ground for exposures that are more manageable. But when confronted with what to do at a given moment, we witnessed a real challenge of extremes this past week.

In the days of film, we would have likely calculated how bright the moon was, assumed a N minus 2 or 3 development, and seen how much exposure we could capture of the ground. Then in printing, a really good job of burning in the moon would have probably also been necessary for the print. Some examples from photographic history do come to mind.

Last week, I instinctively just hand bracketed the exposures assuming I would put them together after the fact, as digital can often allow. But with the 600mm lens I had borrowed from Canon, the magnification was such that the time lag of manually adjusting the shutter speed and taking the second exposure allowed the moon to drift. Consequently, small differences in feature location between the exposures emerged with the long magnification that the lens provided.

The result was that very few of my photographs line up well. And this might be ok, but there were other factors I ran into, the glow around the moon itself that needed to be preserved as well as the color coming through in the sky around it.

My manual exposure changes were simply too different in moon location to do a standard HDR integration after the fact, although I'm still thinking that one through.

Doing a standard HDR integration should have been obvious to me at the time, and not unlikely what my students were already doing with their auto bracketing habits. I simply should have set up a bracketing sequence on the camera for a very wide range, and had the camera do a continuous stream of exposures to encode the range as automatically and as independently from any human jiggle and as close in time as possible. That would have minimized any difference in location of the moon relative to the proper exposure and the over-exposure of the image designed to record some ground detail. Then a standard HDR integration might have worked well.

In other words, I should have simply done an HDR set, and a standard HDR integration after the fact.


The moon exposure was f8 at 1/400 of second, the mountains below f8 at 1/8, six stops of exposure difference which is not an unusual spread for HDR at all.

The two images were opened into Photoshop Layers, aligned, and the moon shot masked to only let the moon through, with considerable work on the still imperfect mask. The lens exhibited some chromatic aberration not completely eliminated by the Adobe RAW controls, which had to be hand tweaked.

Although it seemed worth including here as an example, it is still very much a work in progress.

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