dosk wrote:
> May be quite simple, but I still don't understand it ...
OK, I'll try We start with a cone of light ...
(no, wait just a "flashback" :^)
an analogy might be to consider spot metering to be similar to
a long telephoto lens and centerweighted more like a normal to
semi-wide lens. the telephoto (& spotmeter) gives a much smaller
field of view (metering).
here's the deal : in centerweighted, the meter "sees" the
entire frame and meters the overall, tending to read "more"
toward the low center of the frame in its averaging. A, more
or less, simple weighted average.
A spotmeter will restrict its metering to a small section of
the viewfinder, much like selectable AF points do. With a tele
lense, this area will be a much narrower field of view than w/
a wider lens, of course - but either will "limit" the metering
to a particular small section within the frame.
This way one can meter a particular part of the scene, such as
an 18% grey substitute, and let the rest fall into line from there.
Or one can do "semi-zone system" placements of this tone via
the exposure compensation dial. I say semi-zone, because rarely
will one shoot an entire 35mm roll in a single exposure/development
zone system arrangement
---------------------------------------------------------
Bill D. Casselberry ; Photography on the Oregon Coast
http://www.orednet.org/~bcasselb
[EMAIL PROTECTED]
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