Tips /
Take Control - Change 3 Defaults /
3 - Matrix or Evaluative Metering
Your camera has a light meter that measures the amount of light
in a scene.
What this light meter "sees" can be changed.
There are three light metering patterns:
• Matrix (Nikon) and evaluative (Canon)
• Center weighted
• Spot
Matrix/Evaluative Metering
When using matrix/evaluative metering, the light meter measures
many areas, or zones, on the frame.
The Nikon D70s measures 1,005 points, using a color sensor separate
from the imaging sensor.
The Canon Digital Rebel XT measures 35 zones.
Before the shutter opens, the data from these many points or
zones, is compared to thousands of patterns, called algorithms,
stored on your camera's computer.
If there's a match between the pattern of the scene you're photographing,
and one of the algorithms, the computer will base the exposure setting
on the matching algorithm.
The reading at the focus point will be given greater weight,
as this is probably the subject of the photograph.
Therefore, when you're using matrix/evaluative metering, set
your focusing system to where the focus point is decided by the
camera (see
Automatic Focus Area Selection).
Matrix/evaluative metering works well—but not all of the time.
Where setting the best exposure may be tricky—compare matrix/evaluative
metering with center-weighted or spot metering.
When is setting the exposure tricky?
Contrasty scenes and backlighted subjects can confuse matrix/evaluative
metering systems.
Your judgment may be better than that of your camera's computer.
Use center-weighted or spot metering.
Center Weighted Metering
With center-weighted metering, the light meter measures most
of the light (60 to 75% depending on the camera) in the central
area of the frame.
For example, if you're photographing a landscape, and you don't
want a bright sky throwing off the exposure, point the central area
of the frame down, removing the sky from the frame.
Lock in the exposure using the autoexposure lock button (AEL
button on Nikons, star icon button on Canon Digital Rebel XT).
Then, recompose your photograph in the frame.
Go to
AEL/AFL.
Spot Metering
With spot metering, the light meter measures a small area in
the center of the frame.
This area may be from 1% to several percent of the entire area
of the frame.
On some cameras, you can adjust the size of the area.
For example, if you're photographing an eagle nest against a
bright sky, point the center of the frame at the nest.
As described above, lock in the exposure using the autoexposure
lock button (AEL button on Nikons, star icon button on Canon Digital
Rebel XT).
Then, recompose your photograph in the frame.
Go to
AEL/AFL.
None of the Above Work for this Situation
If you're photographing a subject that's very light colored or
toned, or dark colored or toned, all of the above metering systems
will fail.
Your judgment will be 100% better.
For example, if you're photographing snow in the sun, all of
the above metering types will underexpose (too dark) the snow.
Similarly, if you're photographing the face of a gorilla, all
of the above metering types will overexpose (too light) the gorilla's
face.
You have to measure the light in the scene on a surface that's
medium colored or toned.
Go to
Light Meters Are Stupid.
