Ansel Adams knew about this long ago and has an excellent discussion about
it relatively early on in Book 2, "The Negative" of his classic
trilogy. IIRC, he (Adams) found that most light meters overexpose by an
average of about 1/3rd f-stop . . . which correlates to a slightly darker
than 18% gray (something slightly less than that) . . . and calls the
over-exposure shift built into the meter as the "K-factor."
-- John
At 06:00 PM 3/22/2005, Winsor Crosby wrote:
>One thing noticed by people who are now using histograms on cameras and
>in software is that metering something that is evenly lit puts all the
>exposure to the left of the center of the histogram. I was surprise to
>find that meters are really calibrated to 12 percent gray which is a
>half stop away. Here is a better explanation than I can offer:
>
>http://www.bythom.com/graycards.htm
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