Matrix-metering adds computer analysis to the
averaging process. Its programming breaks up
the scene into regions and then tries to identify
the best exposure based on the patterns of
intensity.
The computer in the camera has a
library of standard scenes, like sunsets and portraits.
For example, a very bright overall scene
with one dark area might be flagged as being
backlit. The metering system would then suggest
(or automatically adjust) the exposure to give
the dark region more light, at the risk of washing
out the bright background.
That scenario is a generalization. Matrix-meter
programming is the heart of most of the modern
DSLR’s automatic modes. Each vendor developeds
its own algorithms (computerized mathematical
formulas), and the finer points are proprietary
secrets. Some cameras come with tens of thousands
of resident sample scenes, which the computer
uses to arrive at its suggestions. Be sure to
study the options and controls available for your
built-in meter; each model has its own quirks
that can only be understood by using them.
Matrix-metering is a major improvement over
the coarse results provided by a basic averaging
system. If you wish to rely on either, practicing
to the point of familiarity is in order. It’s also a
good idea to check the results, if the image is
important. That is especially true if the picture
contains an unusual mix of light and dark areas
or has high contrast.
The better DSLRs also offer a spot meter mode.
This design limits the meter’s action to a very
small area. Hand-held spot meters can read
very small circular areas. The size will depend
on the distance from the meter to the subject.
In-camera meters vary; the best ones measure
about 4mm directly off the sensor.
This image
shows a picture that I took using a spot meter.
The large areas of black, coupled with the very
bright stage lights, would have challenged any
other metering system.
This image was taken under extremely contrasty lighting
conditions; it was exposed, and then processed, to
allow the center of interest, the actress, to be presented
in normal contrast.
Spot meters, like averaging meters, read the target
and assume it is reflecting 18-percent gray.
I used a hand-held spot meter when choosing
an exposure for the above image. I pointed it at the
actress’ tights, which were very close to the right
tone. The night was dark, except for the big
stage lights, and the exposure was 1/15th of a
second at f/1.2 with an ISO of 1600. It helps to
practice holding the camera very still.
Incident meters still use 18-percent gray as a reference,
but they average the light falling on a
side of the primary subject facing the camera.
This type of meter is especially handy when
photographing a scene with multiple lighting
sources. The dome can be aimed at each source
to gauge its effect on the exposure, and then at
the camera to find the total effect on the picture. The better models, like the Sekonic L-758dr, also
can measure flash output. If you decide to get
serious with advanced lighting effects, an incident
meter is a nice addition to the gadget bag.
To hone your skills, start taking pictures in more
challenging lighting conditions. Use the meter
and experiment with its different modes. Your
camera should offer a way to rapidly set an
exposure compensation.
This adjusts the effective
exposure in small amounts, usually equal to a
one-third f/stop value, while leaving the actual
exposure-value setting the same. Examine the
results, paying particular attention to the way
very bright and very dark areas are recorded.
The goal is to find the settings that hold the
most detail. | 
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