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[OM] Re: The myth of 18 percent gray

Subject: [OM] Re: The myth of 18 percent gray
From: hiwayman@xxxxxxx (Walt Wayman)
Date: Wed, 23 Mar 2005 05:07:14 +0000
I'm surprised some of y'all are surprised by this.  Not only did AA cover the 
subject long ago, but within the last year I, dumb as a box of rocks though I 
may be, posted right here a quote about it from the National Geographic 
Photography Field Guide, which I shall repeat here, since apparently nobody 
paid any attention then.

"Scientific studies now indicate that an average scene actually reflects 13 
percent (not 18 percent) of the light that falls on it.  For the sake of 
consistency, gray cards have continued to be 18 percent gray, as is the one in 
this book.  When using any 18 percent gray card for substitute metering, 
increase exposure by a half stop (+0.5 compensation factor) for most subjects, 
as Kodak recommends.  If the subject is very light -- a snow-covered landscape, 
for example -- decrease exposure instead by a half stop (-0.5 compensation 
factor) from the gray card reading.  This will help maintain detail and 
texture."

Walt, who despite all the BS is occasionally informative

--
"Anything more than 500 yards from 
the car just isn't photogenic." -- 
Edward Weston

 -------------- Original message ----------------------
From: "John A. Lind" <jalind@xxxxxxxxxxxxx>
> 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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