DP Review Needs a Lesson (or I do)

Started Apr 13, 2014 | Discussions thread
bruxi Regular Member • Posts: 318
Re: DP Review Needs a Lesson (or I do)

In an article on the upcoming lunar eclipse, DPReview explains why a photo of a lit moon at night will overexpose the moon's features:

The moon is very bright, even during an eclipse. If you rely on the internal exposure settings in your camera you’ll likely get a picture that’s overexposed and has no detail. That’s because the exposure meter in the camera expects everything to be neutral gray and the moon is bright white.

Sorry, but unless I'm mistaken, this is incorrect. A meter that expects gray will underexpose a bright white subject. The intuition is that the meter, expecting gray and seeing brightness provides a reading that corresponds to a very bright gray, rather than a merely bright white, and reduces the exposure accordingly, correctly for a gray with that brightness, but too much for white. (This, anyway, is the account given in any standard explanation for photographing in snow or white sand.)

Don't get me wrong.  I have no doubt that a shot of a bright moon against a black sky will blow the moon's highlights under standard settings that average the light in a frame. But that's just because the dynamic range is unmanageable. Spot metering the moon solves that problem (though not the one that cuts in the other direction, namely that the moon is white, not gray).

I get what the DP Review writer is saying. He's saying the camera will meter properly if everything in the frame is neutral grey (ie. like an 18% grey card). That is true. Shooting the moon is different, since it's not a uniform grey card, it's typically mostly black with a bright subject (the moon). So unless you use and nail spot metering, you are using average metering and the dark sky causes overexposure of the moon. Anyway, he's not wrong, I just don't think you understood what he was saying.

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