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Setting Exposure /

13.2 - More about Light Meters

What Your Light Meter "Sees"

Your light meter can be set to see different parts of the scene.

Multiple-point Metering

Your light meter can be set to measure many different parts of a scene.

This is called matrix metering (Nikon) or evaluative metering (Canon).

The multiple measurements are compared to exposure algorithms stored in the camera computer.

The lens opening and shutter speed are set according to the best match between the multiple measurements and the algorithms.

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.

Let's say you're photographing a landscape.

You don't want a bright sky throwing off the exposure.

So, 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 Canons).

Then, recompose your photograph in the frame.

Go to Autoexposure Lock.

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.

Let's say 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.

Then, recompose your photograph in the frame.

Go to Autoexposure Lock.

Light Meters Are Stupid

Light meters give you acceptable exposures most of the time.

However, there are several situations where the light meter will give you the wrong exposure.

You'll learn about these situations below.