On Wed, 13 Jan 1999, Garth Wood wrote:
> I believe the original poster had the following in mind.
> All "real" subjects are composed of a set of reflective surfaces (say, a
> human face) in a large variety of planes with respect to the taking lens --
> almost infinite, in fact, and an averaging meter, "looking" at all these
> planes, integrates them.
> Metering off of a grey card in front of your "real" subject presents you with
> a subject in a single plane. If you hold the card vertical (i.e., parallel
> with respect to the longest axis of your subject), your meter reading off the
> card may be slightly biased to reflections perpendicular to the focal axis of
> your taking lens. Tilting the card slightly (and it's always a "by guess and
> by golly" operation) *may* produce a value which is closer to 18 0rey
> integrated across the range of planes which the true subject (rather than the
> card) presents to the taking lens.
> In my opinion, this is a harmless thing to do, but the amount of extra
> precision it's attempting to incorporate in the integration of an average
> reading is probably lost. After all, your "guesstimate" of just how far to
> tilt the card could be wrong. In any case, I'd be willing to bet that, for
> practical purposes, it doesn't make much difference to the final exposure.
I disagree. Take a simple shot of a person sunbathing at noon. If you
want to place your exposure based on their front (the side facing up),
you would be best served by angling the card on that plane. If you want to
assess the difference between the light falling on their face as opposed
to their sides (the one facing you and the lens axis) a quick check by
angling (card or hand) will tell you very quickly. This can be done in
seconds (and with a camera with some
sort of exposure lock or display panel (like the OM2SP) without
drawing attention by bringing the camera up to your eye.
This only provides the user with extra information. The precision is then
left up to the user.
*= Doris Fang =*
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