photokaboom

Learn Photography

Beecher's Handouts >

12 – Set the Exposure

1 – The Light Meter

We've looked at how aperture and shutter speed are used to control the amount of light reaching the sensor.

How do we measure the amount of light?

Your camera contains a light meter for that purpose.

The light meter measures the amount of light that will strike the sensor.

When you depress the shutter release slightly, the light meter turns on.

You're taking a light reading.

You're measuring the light with the light meter.

Once the amount of light is known, the aperture and shutter speed can be set.

2 – More About Light Meters

Beginners should come back to this section later.

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 aperture 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.

For example, let's say 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 Nikon cameras and others, asterisk-icon button on Canon cameras).

Then, recompose your photograph in the frame.

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 Nikon cameras and others, asterisk-icon button on Canons).

Then, recompose your photograph in the frame.

3 – Exposure Modes

q

Your camera has exposure modes.

Exposure modes are often located on a knob on the top of the camera.

The modes are designated by letters and icons.

We'll look at the letters here, and then the icons below.

Exposure Mode Letters

Nikon Cameras & Others

On Nikon cameras, and many other cameras, the exposure modes include the following.

Auto

Auto

P

Program

A

Aperture priority

S

Shutter priority

M

Manual

Canon Cameras

On Canon cameras, the exposure modes include the following.

Auto

Auto

P

Program

Av

Aperture priority

Tv

Shutter priority

M

Manual

What does each of the above exposure modes do?

Auto

The Auto exposure mode does two things.

1) It uses the program exposure mode (described below).

2) Sets many defaults on the camera.

You can't change any of these settings yourself.

For example, let's say you need to use flash to brighten the shadow under someone's hat.

You won't be able to pop the flash up.

You need to use the following exposure mode to have control of your camera.

Program

Program, P, is the most convenient exposure mode.

You don't have to do anything.

You can ignore aperture and shutter speed.

That's a problem.

If we don't have to use these tools, our photographs won't be as good.

Aperture-priority Exposure Mode

Aperture-priority exposure mode, Av or A, is used for changing the depth-of-field.

You set the aperture, the camera sets the shutter speed.

By changing the aperture, you can change the depth-of-field.

We'll explore depth-of-field later.

Shutter-priority Exposure Mode

Shutter-priority exposure mode, Tv or S, is useful for freezing or blurring movement.

You choose the shutter speed, and the camera selects the aperture.

Manual Exposure Mode

Manual exposure mode, M, is useful if you want to bracket your exposures.

Bracketing is the taking of several photographs of a scene at different exposure settings.

Many photographers now use automatic bracketing or use exposure compensation.

Exposure Mode Icons

q

Here's what the most useful icons do.

Face

Use the face icon for portraits.

The camera may select a physically large aperture (less depth-of-field) to blur the background.

The camera may also select a color balance that's optimized for skin tone and may reduce the contrast as well.

Mountain

Use the mountain icon for landscapes.

The camera may make the color more vivid.

Flower

Use the flower icon for close-ups.

The camera may select a physically small aperture (more depth-of-field) so more of the subject is in focus.

Jogger

Use the jogger icon to freeze motion.

The camera will select a fast shutter speed to freeze the subject's motion.

Figure w/ Moon or Star

This icon is for night portraits.

The flash will illuminate the person.

The shutter will stay open longer to gather light from the dimmer background, so it is also well-exposed.

Movement in the background may be blurred.

Scene Modes

Your camera may have scene modes.

Scene modes are for:

o The above situations.

o For tricky exposure situations, such as candlelight, fireworks, and so forth.

4 – Bracketing

Bracketing is the taking of several photographs of a scene where different amounts of light reach the sensor.

Normally, as you change the shutter speed, the aperture will change as well.

Or, as you change the aperture, the shutter speed will change.

In both situations, the amount of light reaching the sensor is the same.

Each photograph will have the same brightness as the others.

However, when bracketing, the amount of light is varied to produce exposures each with a different brightness.

Bracketing is done when you're unsure of the best exposure.

How to Bracket

Many cameras have automatic bracketing.

You can set your camera to take several different exposures.

You can also use exposure compensation, which is described below.

5 – Exposure Compensation

Exposure compensation allows you to override the light meter's exposure setting.

Let's say you're changing the exposure settings using the following exposure modes:

• Aperture-priority exposure mode (A or Av)

• Shutter-priority exposure mode (S or Tv)

The brightness of each exposure stays the same, even though you change the aperture or the shutter speed.

When you change one, the camera changes the other, to keep the exposure brightness the same.

You have to use exposure compensation to make a photograph lighter (overexposed) or darker (underexposed).

Uses for Exposure Compensation

Richer Colors

Let's say you're photographing red petroglyphs on a canyon wall in Nevada.

You want the photograph to be a little darker, underexposed, to make the colors richer.

Set the exposure compensation feature to -1.0.

The petroglyphs will be a deeper red.

Bracketing

Let's say you're photographing the sunset in Lugarno.

Sunsets can look good lighter and darker.

So, you photograph the sunset at different exposure compensation settings.

How to Use Exposure Compensation

To use exposure compensation, hold down the +/– button, and turn a knob on your camera to adjust the compensation.

A plus setting makes the photograph brighter.

A minus setting makes it darker.

A Few Canon Cameras

With a few Canon cameras, you have to switch the on/off switch on the back of the camera to the slash icon.

Then, do the following.

1) Fill the frame with the part of the scene that you want to photograph.

2) Turn on the light meter (depress the shutter release slightly).

3) Turn the knob on the back of the camera to adjust the exposure compensation.

Warning

When using exposure compensation, most cameras display a +/– icon on the LCD screen.

Check periodically to make sure the exposure compensation icon is absent—unless you're using the feature.

Let's say you photographed a 1950s car.

You set the exposure compensation to –2.0 to make the chrome bumper stand out from the aqua paint of the car.

That was yesterday.

Today, you're photographing a friend's baby, Hunter.

You remember to check for the +/– icon.

You change the exposure compensation to 0.0 from –2.0 before photographing Hunter.

6 – Autoexposure Lock

You can point your camera at part of a scene-measure the light-and can lock in that exposure.

Let's say you're photographing the Matterhorn from the village of Zermatt.

The mountain is in the sun.

The village is in the shade.

Your camera may set the exposure for the shady part of the scene, Zermatt, and not the Matterhorn.

If so, the Matterhorn would be too bright.

Use the autoexposure lock button to make sure the camera sets the exposure for the mountain, and not the village.

Do the following.

How to Lock in the Exposure

Nikon Digital SLRs

Look for the AEL button.

It's near where your right-hand thumb can reach it.

When you press and hold the AEL button, the exposure is locked in.

1) Press the shutter release slightly to turn the light meter on.

2) Fill the frame with the part of the scene that you want to use to set the exposure.

In the example, point the camera away from the bright window.

3) Press the AEL button and hold.

4) Recompose the scene in the frame.

5) Press the shutter release.

Canon Digital SLRs

Look for the button with an asterisk icon.

It's near where your right-hand thumb can reach it.

When you press and release the asterisk-icon button, the exposure is locked in until the light meter shuts off.

1) Press the shutter release slightly to turn the light meter on.

2) Fill the frame with the part of the scene that you want to use to set the exposure.

In the example, point the camera away from the bright window.

3) Press and release the asterisk-icon button.

4) Recompose the scene in the frame.

5) Press the shutter release.

Make sure the light meter doesn't turn off before you've pressed the shutter release.

If it does, start over.

Autofocus Lock, Too?

The autoexposure lock button often does double duty as an autofocus lock (AFL) button.

In your camera menu, you can set the button to:

" Lock in both the exposure and the focus.

" Lock in only the exposure.

" Lock in only the focus.

You may want to set the button to

lock in only the exposure.