Tom, your explanation differs with what I have read in many places. For
example, Burian and Caputo, in the National Geographic Photography Field
Guide (p. 137), write:
"Scientific studies now indicate that an average scene actually reflects 13%
(not 18%) of the light that falls on it. For the sake of consistency, grey
cards have continued to be 18 percent grey, as is the one in this book.
When using any 18% grey card for substitute metering, increase exposure by a
half stop."
Your explanation of the way meters are calibrated makes good intuitive
sense, and, as you say, it's not relevant. However, in your example, a scene
of foliage reflects approximately the same amount of light as an 18% grey
card. This fact can only be used to deduce that the foliage reflects 18% of
the light that falls upon it, not that foliage is an "average" scene.
As I have understood things, the 13% standard simply indicates that "they"
(bless their hearts, whoever they are) have decided that the average scene,
whatever that is, actually reflects 13% of the light that falls upon it.
Of course, as long as one knows how to meter, this is all kind of academic,
but I am keen to know what the real story is.
Cheers,
Mike
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Tom Rittenhouse
Sent: July 12, 2001 21:36
To: [EMAIL PROTECTED]
Subject: Re: 18% Gray (again)
Sorry, I didn't know what I was talking about here. See "Ah
ha (was 18% gray) for the answer.
--Tom
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