Interesting. I too have found that foliage, trees, mountains, which are
all typical of an Ansel Adams photograph, are very close to 18%. On the
other hand, typical caucasian skin is at about zone VI or 13%. And since
most cameras are used to take snapshots of the rug rats, a meter
calibrated to that value serves the average point and shooter quite well.
Paul
Tom Rittenhouse wrote:
>
> Gee whizz, wowie!
>
> Well I must be old then because I do remember why 18% was
> chosen. Go out and meter a field of foliage and compare that
> to your gray card reading. Average reflectance of scenes is
> 18% If you meter that as 13% reflectance you will over
> expose it. It is simple the average scene reflects 18% of
> the light that hits it. It is not an arbitrary value. It is
> a fact of the real world out there.
>
> As for Ansel Adams 12.5% would give zone VI, so 13% would
> fit the zone system exactly. However, photography goes back
> 160 years, according to you guys no one knew what they were
> doing for the first 159 of them. You quote "Shutterbug" to
> me as proof that I and every one else have been doing it
> wrong for all those years.
>
> As for checking my meters, the four of them are with in 1/3
> stop of each other, and the incident meter matches the
> reflected reading from a gray card. BTW, why does an
> incident light dome for a meter transmit 18% of the light?
>
> I have heard that meters, especially built in meters, are
> calibrated with a 4 stop neutral density filter from a
> calibrated standard bulb. That explains why they would say
> their meter is calibrated to 13$, but that does not change
> the average reflectance of the real world. What that means
> is that the meter is off by a certain percentage for all
> exposures made with it even when you use an accurate
> metering technique. I had thought that the film manufactures
> were being optimistic about their film speeds but the fact
> that adjusting the film speed that same percentage gives
> excellent exposures tends to indicate the meters are in fact
> off by that much.
>
> --Tom
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