Monday, January 14, 2008

Expose Yourself (II)

Last month I took pictures of a nearly full moon and found the best exposure (on my camera) was 1/800 second to keep the grays on the lunar surface from being overexposed.

I was curious whether the same would apply when taking pictures of a crescent moon. Same object, same light source: You’d figure the same settings would give you the same exposure, even if it’s for a smaller part of the same subject.

You’d be wrong.

The picture above was taken at 1/100 second, which turned out best. The ISO film speed equivalent was set to 200 instead of 100, which means not only was the exposure eight times as long, but the sensitivity to light was twice as high.

This is the picture I took using the same settings I had used for the full moon.

This is last month’s picture of the full moon, for comparison.

I don’t think most of us consciously adjust our eyes so we can see the moon properly in different phases. We look up on a clear night, and there’s the moon. We see craters; we see light and dark; some of us see faces.

Cameras aren’t quite so clever yet as our eyeballs, so there’s still some manual adjustment required when we want to use a camera to show other people what our eyes saw so easily.

Next project is to see whether I can tweak the camera so it’ll pick up the very slight—but visible—image of the part of the moon’s face that is in shadow when the moon is reduced to a crescent.

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