> I went and double-checked the setting, and I have it at centre-weighted
> averaging. I set it up this way after getting the E-500 so that it would
be
> similar to the OM-1 metering, which I had become used to.
Interesting! This brings up an oddity that I've noticed, but haven't given
much thought to. It seems that if there is a bright spot of light in the
scene, the averaging meter will get overly driven down. Where averaging
normally takes into account and "averages" the entire pattern area, with my
E-1 and DMC-L1, the image will frequently underexpose. For example, if I
photograph an automobile, but the sun is reflecting off of a bit of chrome,
the picture underexposes. In ESP mode, it does find. With the OM series, it
does fine.
Here is my theory--take it strictly as a theory being submitted for peer
review:
1. Traditional center-weight metering system uses a single sensor
(detector). The pattern is of a single coverage zone and does not use any
segments to isolate portions of the zone out for other purposes. It is an
"averaging" meter in every sense of the word in that it averages the
brightness values of all light falling in that zone to come up with the EV.
In digital camera terms, it's a one-pixel camera. If half the scene was
black and half was white, the sensor would only know of the combined values
which average to a gray. It can't see the black or the white, only the mixed
light.
2. Modern metering systems use a multi-zone detector with multiple "pixels".
This is frequently combined with the AF sensor to get another pinpoint
source of light measurement. So, to achieve an "average" exposure for
"center-weight averaging", the camera combines the values from all pixels
(detectors) within the coverage pattern. In my black/white scene, some of
the detectors see black, some see white and the ones at the transition point
average them together.
3. Multi-segment detectors in modern cameras are weighted in the mix-matrix
per the size in proportion to the whole of the coverage pattern. If there
are three detectors (left surround, center spot, right surround), the
camera's fuzzy logic will mix the values of the three detectors together
based on the percentage of the area of coverage. If the left surround is 40%
of the total, right surround is 40% of the total, the center spot is 10% of
the total.
4. When one of the surrounds (in my 3-detector array) encounters a bright
object (chrome reflecting the sun), it will drive the exposure value of that
particular detector up high. Inotherwords, the average EV of that particular
segment is far higher than the average EV of the entire scene.
5. As the fuzzy logic averages the EV of all detectors together based on the
percentage of coverage area for each detector, the surround, which may have
40% of the coverage will be heavily weighted in the overall average.
6. What this will do is swing the center-weight averaging EV value too far
in one direction as it isn't a true averaging of the entire coverage zone,
but an averaging of the average EV of each detector's coverage areas.
7. Cameras with far more detector segments than three will combine the EV
values in a manner which a computer programmer wrote the code. Most of the
work is devoted to ESP or Matrix metering, little regard is given to
center-weight averaging. It is possible that an engineering flaw in the way
the detectors are averaged is present in the camera. This is probably a
given, because Olympus had stated how the ESP metering in the E-3 was
revised and updated.
Dr. Schnozz
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