Why is the moon exposure rule f/11 instead of the sunny 16 rule?
Asked 2/17/2019
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The sunny 16 rule says that in bright sunlight you can use f/16 with a shutter speed near the reciprocal of ISO. But the looney 11 rule for photographing the moon suggests f/11 at the reciprocal of ISO.
Since the moon is illuminated by the sun, I expected sunny 16 to apply. Why does the moon usually need about one stop more exposure? Is it because the moon reflects less light than a typical sunlit scene?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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The moon's surface is relatively darker than Earth's, with an average albedo of 11% (our gray cards are 18%). Moon phases other than full moon are side lighted, and darker still. Yet we seem to prefer too-bright pictures of the moon, thinking that captures it shining up there against the black sky background. So f/11 more nearly captures that sensation for us.
Originally by user38978. Source · Licensed CC BY-SA 4.0
user38978
7y ago
0
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Yes. The main reason is that the moon is not as bright, reflectively, as a typical sunlit subject assumed by the sunny 16 rule.
The lunar surface has a relatively low average albedo, around 11%, which is darker than the 18% gray reference commonly used for exposure. So even though the moon is lit by the same sun, it reflects less light back toward the camera than a typical bright daytime scene. That pushes exposure toward about one stop more light, which is why f/11 often works better than f/16.
Also, moon phases other than full are side-lit, which makes them appear darker still.
In practice, many photographers also prefer a slightly brighter moon exposure because it matches how we expect the moon to look against a dark sky. So “looney 11” is a useful rule of thumb rather than a strict physical law.
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