Lunar Photography

To obtain an image of the moon large enough to show craters, mountains and other lunar features, use a 500mm or longer lens or telescope. The formula for determining the size of the lunar images on film is: divide the focal length (in millimeters) by 110 to arrive at the lunar diameter (in millimeters) on the film.

It is recommended that the camera be used piggyback or as prime focus on a tracking telescope, however, depending on the size of lens being used, photos can be taken from a tripod. The limiting factor here is to limit the exposure (depending on the lens) to avoid star trails. Example: for a camera mounted on a tripod using a 50mm lens, the exposure can be approx. 12 seconds to avoid star trailing; mounted on a driven telescope, the exposure can be up to 4 minutes. The table listed below shows the maximum exposure times using various lenses with fixed mounts and tracking mounts.

For comparison a penny is approximately 20mm. (Note: this is the size on a 35mm negative not the developed print....)

Exposure Times To Avoid Star Trailing
Lens (in mm)Image Size on Film (in mm)Fixed (tripod)Driven (At Sidereal Rate)
500.4512 sec.4 min.
1000.96 sec.2 min.
2001.83 sec.1 min.
5004.51 sec.20 sec.
100091/2 sec.10 sec.
150013.51/4 sec.7 sec.
2000181/8 sec.5 sec.
2500231/15 sec.3 sec.

The speed (ISO) of the film being used for lunar photography determines the exposure times due to the varying brightness phases of the moon. The higher the speed (ISO) of the fim, the shorter the exposure. The drawback of using super high speed films such as the ISO 3200 is that the finished pictures tend to be very grainy especially when enlarged. The following table gives the exposure times (in seconds) for various speed films at different phases of the moon. Due to atmospheric turbulance and light pollution, it is best to 'bracket' your exposures. Bracketing consists of taking exposures on both sides of the recommended shutter speed.

Lunar Photography Exposure Guide (@f/16)
ISO Film SpeedFull MoonGibbousFirst QuarterThick CresentThin CresentEarthshine
2001/1251/601/301/151/840 to 80 sec.
4001/2501/1251/601/301/1520 to 40 sec.
8001/5001/2501/1251/601/3010 to 20 sec.
16001/10001/5001/2501/1251/605 to 10 sec.
32001/20001/10001/3001/2501/1252 to 5 sec.

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