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Re: [OM] Grey card cont.

Subject: Re: [OM] Grey card cont.
From: Garth Wood <garth@xxxxxxxxxxxxxxx>
Date: Wed, 13 Jan 1999 08:50:40 -0700
At 06:42 AM 1/13/99 -0700, Patrick Greenlee wrote:
>>Also, who says it needs to be in focus? As long as it is in the correct
>>lighting for the subject, at a slight angle, it should be fine.
>
>'splain me the slight angle, angle.  I thought you would want to avoid a
>specular reflection (glare) getting reflected at the metering thingy and
>other than that as near broadside as is convenient shouldn't hurt, nicht
>var?

Patrick:

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.

Garth

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