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15 – Light Meters Are Stupid

1 – Introduction

The light meter in your camera is stupid, some of the time.

For example, this white hydrangea in the sun, is too dark.

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The flower actually more looked liked this.

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Light meters "think" everything is average toned.

So, when you photograph something that doesn't have an average tone, the exposure will be too bright or too dark.

If your light meter "sees" this white square . . .

. . . it will "think" there's lots of light.

It will darken the square.

Similarily:

If your light meter "sees" this black square . . .

. . . it will "think" there's little light.

It will brighten the square.

Here's a photograph taken from a cliff of a snowy valley.

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Click Photograph to Enlarge

The light meter measured lots of sunlight reflecting off of the snow.

The light meter set the exposure to make the snow look average—gray.

The valley actually looked like this.

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Click Photograph to Enlarge

Here's an example of photographing a dark subject.

The gloves are too bright.

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Click Photograph to Enlarge

The gloves looked like this.

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Click Photograph to Enlarge

2 – Why Are They Stupid?

If you wish, you can skip this explanation.

However, if you read on, you'll be one of the few photographers who understand completely how their light meters work.

Measuring Reflected Light

Causes Errors

Light meters in cameras measure light that's reflecting off of the subject.

Camera light meters can't measure how much light was absorbed by the subject.

White snow in sun absorbs very little light, and reflects a lot of light.

So, the light meters "sees" a lot of light, and makes the exposure too dark.

Black gloves absorb lots of light.

So, the light meters "sees" very little light, and makes the exposure too bright.

Example

In the example below, there are seven stops of light falling on the scene.

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Not all of those seven stops are reflecting back to the camera, however.

White Bowl

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Six stops of light are reflected back to the camera light meter from the bowl.

One stop of light is absorbed by the bowl.

Two stops of light are reflected back to the camera light meter from the bowl.

Black Velvet

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Five stops of light are absorbed by the black velvet.

Two stops of light are reflected back to the camera light meter from the black velvet.

What the Light Meter Sees

So, there are seven stops of light illuminating the scene.

But, if you take a light reading from the bowl, the light meter will see six stops of light.

Or, if you take a light reading from the black velvet, the light meter will see two stops of light.

What's a Light Meter to Do?

Pity the poor light meter.

There are six stops of light from the white bowl.

There are two stops from the black velvet.

How can it correctly decide what to do when there's such a big difference in light reflecting from the scene?

If You Use the Bowl to Set the Exposure

If you use an exposure setting made from the light coming from the bowl, this is what you get.

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The light meter "sees" that there's lots of light reflecting off of the bowl.

The light meter "says:"

Wow, it's bright out there. I better turn down the exposure.

If You Use the Velvet to Set the Exposure

If you use an exposure setting based on the light from the velvet, this is what you get.

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The light meter sees that there's very little light reflecting off of the velvet.

The light meter says:

Wow, it's dark out there. I better turn up the exposure.

How do you get the correct exposure?

3 – Getting the Correct Exposure

How do you photograph subjects that are bright or dark?

There are four methods.

Method #1 – Use

Exposure Compensation

This method uses the exposure compensation feature of your camera.

Light Colored/Toned Subjects

You need to overexpose light colored/toned subjects that are in bright light.

Set the exposure compensation feature on your camera to +1.7.

Be sure to set the exposure compensation back to 0.0 when you're done.

Dark Colored/Toned Subjects

You need to underexpose dark colored/toned subjects that are in bright light.

Set the exposure compensation feature on your camera to –1.7.

Take a photograph.

Be sure to set the exposure compensation back to 0.0 when you're done.

Method #2 – Measure

Something More Average

In this method, you look around the scene for something that's average colored or toned.

This object must be in the same light as the subject, of course.

1) Find something in the scene that is average colored/toned.

For example, in the snowy valley scene, this tree bark was medium toned.

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In the photograph of the gloves, the picnic table was medium toned.

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2) Fill the viewfinder with the average colored/toned part of the scene, and set your exposure.

Lock in this exposure by using the automatic exposure lock feature (AEL button on Nikon cameras and others, asterisk-icon button on Canon cameras).

3) Then, point your camera at the scene you want to photograph, and press the shutter release.

Method #3 – Gray Card

You can use an 18% gray card.

Hold the gray card in the same light as the subject.

Measure the light by pointing your camera at the card.

The photograph below is of a gray card held in front of the hydrangea.

The camera light meter measured the light reflecting back from the gray card.

The light reading was 1/500th at f/8.

This exposure was locked in using autoexposure lock.

Method #4 – Incident Meter

You can use a separate light meter.

The light meter in your camera is measuring the light reflected from the scene.

As we have seen above, this can confuse the light meter.

A separate light meter can take incident measurements.

An incident light reading is of the light falling on the scene—not the light reflecting back at the camera from the scene.

Therefore, an incident light reading is not confused by how much light gets absorbed and reflected from the scene.

To take a light reading, place the meter in the scene, and point it back at the camera.

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4 – Be Careful with Backlighting

As discussed in the Lighting Contrast section, most digital sensors cannot record scenes that have both dark and light areas.

You have to choose which part of the scene to record properly, the bright area or the dark area.

Light meters don't know what is important in a scene.

You have to decide.

In the example below, the light meter won't know whether the sky is more important to you—or the parrot.

Example

Let's say you're on the dock at Key West and the sun is setting.

You're taking a picture of a man with the parrot on his shoulder.

You expect the colors of the parrot will look good with the colors of the sunset behind the bird.

When you look at the photograph, however, the sunset looks great, but the parrot is a dark silhouette.

The above situation is called backlighting.

Backlighting can confuse even sophisticated light metering systems.

How do you measure the light better than the light meter?

Take the light reading from the parrot, not the bright sky.

There are three methods.

Method #1 – Walk Closer

Walk up to the parrot, and measure the light on the parrot.

Lock in the exposure with the auto exposure lock button (AEL).

Then, step back, and take the photograph.

Method #2 – Spot Metering

Switch your light meter to spot metering, if your camera has this feature.

When your camera is set for spot metering, it is measuring the light in a small portion of the viewfinder.

Set your exposure by pointing the spot metering zone at the bird.

Lock in the exposure with the auto exposure lock button (AEL).

Then, take the photograph.

Method #3 – Add Light

You can also add more light to the man and bird.

Use fill flash or a reflector.

Then, the sensor can record the scene properly.