FWIW, these facts usually get reviewed each time someone asks about
variances in meters. Apparently, different manufacturers calibrate to
different standards. Some use ANSI, others . . . well, whatever they
choose.
John Shaw and Larry West alerted people to the wide variances of
meters years ago and shared their 'Sunny 16' calibration technique in
books and seminars. Of course they weren't talking about calibration
standards but rather sloppy quality control as some meters were 'off'
by 2 to 3 stops!
hth/ScottGee1
On Wed, 23 Mar 2005 05:07:14 +0000, Walt Wayman <hiwayman@xxxxxxx> wrote:
> 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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