One part of Michael's answer to long exposure caught my eye.

He stated that most camera light meters would find it difficult to meter dimly lit scenes such as a landscape illuminated only by the moon.

Would a handheld meter with a very narrow angle work for determining settings for the moon, by pointing directly at it? How about using the incident / reflected meter against a moon-lit landscape, with no other light pollution?

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    There's a big difference between metering/exposing for a photo of the moon itself, and metering/exposing for a photo of a moonlit scene. – osullic Apr 25 '18 at 21:02
  • @osullic Yup. I know. I want to know if both are possible. – Calyth Apr 25 '18 at 21:05
  • I do not think I said anywhere that in-camera light meters have trouble with the moon. They have trouble with very dim moonlit landscapes. I've edited the original answer and this question to clarify that. – Michael C Apr 26 '18 at 4:50

The moon as seen from the surface of the Earth is lit directly by the sun, unless it is during a new moon. It's very easy to meter the moon with a sufficiently narrow enough light meter. Even built-in camera meters can do it if the lens magnifies the moon sufficiently to occupy the full area of a camera's spot meter. Just remember that an uncompensated reflective meter reading will assume you want the metered area to be halfway between white and black. If you want the moon to appear bright, you'll need to compensate by exposing a stop or two brighter.

Or for photographing the moon itself you could just use the "lunar 11" rule-of-thumb that is similar to the "sunny 16" rule-of-thumb when the moon (or sun) is about 20° or more above the horizon. "Lunar 11" says to use a shutter time that is the reciprocal of your ISO with f/11. As usual, atmospheric conditions can affect how much of the sun and moon's light reaches the surface. The "lunar 11" rule-of-thumb assumes a clear, cloud free sky, just like the "sunny 16" does.

The night time landscape under a moon is not directly lit by sunlight. How bright it will be will depend upon how much of the moon's disc is illuminated as viewed from the location in question. It will depend upon how much of the moon's light is absorbed by clouds, water vapor, and other particulates in the atmosphere. It will depend on how high the moon is above the horizon.

Under a very bright full moon high in the sky on a clear, relatively dry, and cloudless night a moon-lit landscape will typically meter at around EV -2 to EV -3, depending on the reflectivity of the landscape. A desert with white sand or a snow covered plain might meter at EV -1 under perfect lunar conditions.

EV -2 to EV -3 is beyond the capability of the internal light meters of even the top professional camera models today. Although some can autofocus down to EV -2 or EV -3, their light meters are rated only to EV 0 or brighter.

There are a few high end electronic handheld light meters that can measure down to EV -5, but somewhere between EV -2 and EV 0 is much more common. Older analog handheld light meters were even more limited. The popular Sekonic L-208 had a range of EV 3 to EV 17. The Sekonic L-398A Studio Deluxe III had a range of EV 4 to EV 17 for incident metering and only EV 9 to EV 17 for reflective metering. EV 3 is five stops, or 64 times brighter than EV -2.

When the moon is not full, or lower in the sky, or partially or fully obscured by clouds, or diffused by high humidity or dust and other particulates, or any combination of these factors, the landscapes it illuminates are very quickly too dark to be effectively metered by the vast majority of available light meters. Even the top end meters, such as the $600 Sekonic Speedmaster L-858D-U, can't keep up for very long as a night landscape can be significantly darker than EV -5.

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Light meters are calibrated to render a middle gray. Point the meter at target sheet of white paper and expose per the meter reading and that paper will reproduce as middle gray. Point the meter at a charcoal paper and that paper will reproduce as middle gray. Point the meter at a middle gray paper and that paper will reproduce as middle gray. Point the meter at the moon are expose as indicated and the moon will reproduce as middle gray.

Now most would agree that the moon would look weird if it reproduced middle gray. Therefore take a reading of the moon and then open up one f-stop and shoot. Next open up two r-stops and shoot, then thee f-stop. In other words made a series. You will find that one of these "more opened up shots will do this trick.

The meter is calibrated to correctly render a medium gray. You must intervene to get the exposure right.

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