In message ,
Jeremy Nixon wrote:

wrote:

You misunderstood; there is nothing wrong with the metering in this
scenario. The scene had the approximate reflectivity of a grey card.

No, there was; if the meter indicates one stop underexposure, but you can
increase three stops and end up with a proper exposure,

What is "proper exposure"?

then the meter was
actually off by two stops.

No, the meter is dumb, and it puts the mid-key scene at middle grey,
which is not *optimum*, unless your goal is to use a JPEG as-is, or
print directly from the camera. In terms of RAW capture, it is a
relatively poor digitization and/or exposure.

You're comparing "trust the meter" at ISO 200
with "don't trust the meter" at ISO 800, and that's not a useful
comparison, because if you trusted the meter in the first situation
you'd trust it in the second and still underexpose by two stops, but if
you weren't going to trust the meter in the first place (and thus be
willing to go up two more stops from what it said at ISO 800) then you'd
have been willing to do so at ISO 200, too, if you could -- leaving the
choices being either underexpose at 200 or expose properly at 800.

I clearly stated that we were a stop under because of *NEEDED* f-stop
and shutter speed! You're going to blur the image now?

Let me try another way. Let's pretend the camera is greyscale (no CFA),
to simplify matters. The camera meters a grey card (or the ~18% grey
scene) as if to wind up with an average RAW value of 400 (fairly
typical) out of about 4000 possible levels. At ISO 100, you fall a stop
short of that with your needed f-stop and shutter speed, so the RAW
output would be 200. Using the same aperture and shutter speed (as
needed), with ISO 800, the average now is a RAW value of 1600. If you
used ISO 1600, the average RAW value would be 3200, and you might have a
few brighter spots clipping past 4095.

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John P Sheehy