A jet airliner flies past the gibbous Moon. Taken with a Nikon D2H DSLR camera and 80-200mm zoom lens at 1/1000th second exposure at f/4 at ISO 250 at 200mm with JPEG file format.

The Moon is illuminated by the Sun, just as the Earth is during the daytime. Because the Moon is just about the same distance from the Sun as the Earth, it gets just about the same amount of light. Therefore when the Moon is full, the exposure for the Moon is just about the same as for a daytime exposure on the Earth. The rule of thumb for front-lit scenes in the sunshine on the Earth is called the "Sunny 16 rule". It means we should use 1/ISO as the shutter speed at f/16 in the sunshine. This means, for example, if you are shooting at ISO 400, to use 1/400th second exposure at f/16. An equivalent exposure would be 1/1600th second at f/8.

This exposure will record the moon as it really is, which is actually quite dark. Our impression of the Moon is usually quite bright though, because it is normally lit by bright sunshine, but seen in the dark night-time sky. So we can usually overexpose the Moon by a full stop to give it the bright appearance that we expect. This leads to the rule of thumb for the full Moon: the "Looney 11 rule" ("Looney" being a word play on "Lunar"). It means we should use 1/ISO as the shutter speed at f/11 for the full Moon if it is high in a clear sky. However, as the Moon's phases change from full to new Moon, more exposure is required as the Moon is less and less illuminated.

As the Moon goes from full to gibbous to quarter to crescent, it goes from directly front-lit to more side-lit to almost back-lit, and requires more exposure, just as a subject on the Earth does. The rule of thumb is expose the Moon by an additional stop for every 1/8 illumination change in the Moon. This means:

The Full Moon shot with a Canon 20Da and 400mm lens with 1.4x teleconverter. 1/250th second exposure at f/11 at ISO 400.

In the image at the top of the page of the jet flying by the gibbous Moon, shot during the daytime, the exposure for the Moon was almost exactly the same as for the blue sky, about 1/1000th second at f/4 at ISO 250. This is two stops more exposure than is called for by the "Sunny 16 rule" which would be 1/250th sec at f/16 at ISO 250. One of these additional stops of exposure is to make the Moon brighter to fit our perception of it, and the other stop is because the Moon is gibbous and not directly front-lit so not quite as much light is illuminating it. 1/1000th sec at f/4 at ISO 250 (exactly the same exposure as 1/250th at f/8 at ISO 250) exactly fits the Looney 11 rule (1/250th at f/11 at ISO 250), plus one stop more open from f/11 to f/8 for the gibbous phase.

In fact, the exposure was made at 1/1000th second at f/4 at ISO 250 because the camera, a Nikon D1H DSLR, was hand held with an 80-200mm zoom working at 200mm. A faster shutter speed was used to minimize movement and camera shake during the exposure because it was hand held at a long focal length.

In the full Moon shot, the ISO used was 2/3 of a stop higher than what was recommended in the table because the Moon was low on the horizon and dimmed somewhat due to atmospheric absorption.

The lesson in both of these examples is that the correct exposure depends on the circumstances. The data given in the tables is a starting point. The correct exposure should be determined by tests and examining the image and histogram on the LCD on the back of the camera.

Notes on Photographing the Moon

Putting something interesting in the foreground with the Moon in the background can make for a more interesting picture. If you are shooting the Moon when it is lower in the sky, or especially near the horizon, you will be shooting through more of the Earth's atmosphere. Just as the Sun is dimmed when it is viewed through thick atmosphere, so is the Moon, so exposures will have to be increased when the Moon is low in the sky. Local atmospheric conditions, such as haze and humidity, can also affect the brightness, and hence the exposure of the moon.

Trying to use your camera's meter will to get the correct exposure for the Moon may work if you use a long focal length and the Moon is large in the frame, or if your camera has the ability to spot meter. Because the moon is usually small in the frame, unless using about 1,000mm of focal length or more, the meter will read mostly the dark sky background and overexpose the Moon. So try to use the rules of thumb listed above, and most importantly bracket your exposures. Bracketing means to take a series of different exposures centered, or bracketed, around the one that you initially think might be correct. With a digital camera you also have the luxury of examining the image you have just shot to see how well the exposure worked.

Although the Moon can appear enormous when it is near the horizon because of the "Moon Illusion", it is really the exact same size as when it is overhead. It is really quite small, measuring only 1/2 degree in apparent size in the sky. With a 100mm lens on your camera, the moon will only be 1 millimeter in size at the focal plane on your sensor in the camera. If your sensor is 22.5 x 15mm, which is the size of many DSLR sensors, that 1 millimeter is going to seem quite small. To make the full moon fill the frame on the short side of such a digital sensor, you would have to use a 1,500 millimeter focal length telephoto lens or telescope.

Also remember that the Moon is moving constantly, both because of it is revolving around the Earth, and because of the Earth's rotation about its own axis. The Moon moves its own diameter, 1/2 degree, in about 2 minutes. As a general rule of thumb, with a 100mm lens, you can shoot for about 2 to 5 seconds before the Moon's movement becomes objectionable in the final image. With a 500mm lens, you can shoot for about 1/2 to 1 second.

Much more information about rising and setting times for the Moon and Sun can be found at the U.S. Naval Observatory's web site.