>Maybe someone could do the math and report back BUT I don't think the exact
>angle of the grey card to the incident light (which may not have a
>perfectly defined direction) and the angle of the meter to the card is
>hyper-critical. What error in stops would be introduced by less than
>perfect alignment, say 5 or 10 degrees from optimum for both card and meter?
>
>Patrick
>
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I believe you are correct in this statement. Notice that Ansel
said "angle to THE light source". No doubt had in mind the
Sun and assumed the subject was in direct sunlight which
is the dominant light source as opposed to skylight that
is integrated from all other directions. This probably gives
the closest agreement for a reflected light meter off of
18 0rey with an incident light meter's hemispherical dome
that integrates the light from hemisphere that defines all
the light sources that are illuminating the subject.
Should all be within a fraction of an F-stop with either method.
This could be verified by going outdoors and using the
spot meter reading from an OM-2S, 3(ti) or 4(t[i]) and
trying different angles on the grey card and seeing if
more than a 1/3 stop difference is even noticed.
Mark Hammons
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