Looney 11 rule

The basic rule is: "For astronomical photos of the Moon's surface, set aperture to f/11 and shutter speed to the [reciprocal of the] ISO film speed [or ISO setting].

"[1] As with other light readings, shutter speed can be changed as long as the f-number is altered to compensate, e.g. 1/250 second at f/8 gives equivalent exposure to 1/125 second at f/11.

Generally, the adjustment is done such that for each step in aperture increase (i.e., decreasing the f-number), the exposure time has to be halved (or equivalently, the shutter speed doubled), and vice versa.

Steps in aperture correspond to a factor close to the square root of two, thus the above rule.

[2] The albedo of the Moon's surface material is lower (darker) than that of the Earth's surface,[3] and the Looney 11 rule increases exposure by one stop versus the Sunny 16 rule.