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Shooting pictures of the moonin Tutorials |
By pgauthier/Philippe (1,803) 
on May 11, 2002 10:53:55 AM CDT
The moon is bright! The moon is bright!The moon is an object hit by direct sunlight. The sunny 16 rules should therefore apply: the correct exposure would be one divided by your ISO rating @ f/16. For ISO 125 film, this would amount to 1/125 of a second @ f/16.But the moon is a bit darker than the average grey card; you should therefore open one more stop to compensate; the correct exposure would then be 1/125, f/11 in the example above. Because the night is so dark, the human eye sees the moon a bit brighter than it really is. Some photographers open one more stop (1/125 @ f/8) to get a slightly overexposed moon in their shots. This simulates the apparent brightness of the moon to the human eye. These values are correct for the full moon. When the moon is not full, it is still a sun lit object, but the light hits it with an angle, creating long shadows. The moon becomes dimmer and you should take that into account. For a half moon, open two stops from the values suggested above. For a thin crescent, open five stops. Don't forget that the moon is MUCH brighter than the average night scene. If the moon is included in a composition exposed for 15 or 30 seconds (a typical value @ ISO 100 in the city) it will appear like a pure white blotch of light, a bit like taking direct pictures of the sun. This can or cannot be cool, according to your tastes.
The moon is small!The sky, from one side of the horizon to the other, is 180 degrees wide. The moon is only half a degree wide. It is therefore a very small target, relatively speaking. Our eyes don't see it that way, because it attracts the attention so much; but the camera does.This smallness is aggravated by the wide angle of view of most lenses. A normal 50 mm lens sees a 46 degrees wide section of any scene. If you point it at the sky, the moon will only take half a degree of these 46, meaning or 1/92th of the width of the picture. In short, the moon will be about 1.5 millimeter wide on a 4x6 inches (10x15 cm) print.
Here are the angle of view of some typical focal lenghts: To get a moon of any significant size on a picture you'll therefore need a very long lens. With a 300 mm tele, the moon will be 1/16th of the frame wide, or about one centimeter on a 4x6 print. Moonscapes are usually taken with very long (1000 or 1200 mm) lenses, or with cameras attached to telescopes.
The moon moves fast!There might be reasons why you'd like a long exposure of the moon, even if you know it would result in a badly overexposed shot. If you go for such a long shot, be aware that you'll probably get some motion blur.The moon goes around the earth in 24 hours; this means that it does a 360 degrees circle in 1440 minutes, or that it travels one degree in four minutes (this is not 100% exact as far as astronomy is concerned, but for photography purposes, its a good approximation). As was said above, the apparent size of the moon is about half a degree. This means that during a one minute exposure, the moon will move a distance equivalent to about half it apparent size. Result: a moon that looks strangely elongated. Astronomers use motorized telescopes to track the moon and the stars. Some short of fitting such a small electric engine on your tripod, there isn't much you can do to prevent motion blur on long exposures of the moon. If you found this article useful, please rate! I have other subjects in mind and popular support will help me overcome my laziness!
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