Depth-of-field

Preview

Depth-of-field

First, what's depth-of-field?

If you focus on the light on your desk, the light is sharp.

But, what's in front of the light, and behind, may or may not be acceptably sharp.

The zone of what's in focus is called the depth-of-field.

Depth-of-field Preview

Many digital SLR (DSLR) cameras have a depth-of-field button.

The depth-of-field preview button helps you determine the size of the zone of what's acceptably sharp.

The button is usually located near the lens.

Try This

1) Set your exposure mode dial to A or Av.

2) Set the aperture to f/16 by turning the control knob.

3) Focus on something that's about eighteen inches away from you.

4) Looking through the viewfinder, note how the more distant objects are not in focus.

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f/4

In the above photograph, the paper weight is sharp.

That's where the lens was focused.

Because the aperture was at f/4, the plant in the background is blurry.

This photograph has little depth-of-field.

5) Press the depth-of-field preview button and hold it down.

The more distant objects are now sharper.

That's because you're now looking through the lens at f/16, not at f/4.

Yes, the viewfinder is dark.

However, with a little practice, you can become more adept at using this feature.

For example, you'll learn to look at the edge of the subject, to see if it's in focus.

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f/4

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f/16

In the second photograph, with an aperture at f/16, the plant in the background is sharper.

Which photograph is better?

In this example, the paper weight stands out from the blurry background in the photograph taken at f/4.

A Reason for

Poor Composition

The aperture is always wide open (physically big, but with a small number, like f/4), until you press the shutter.

This feature allows lots of light to enter the viewfinder, making it easier to see the scene.

But, whenever you're looking through your viewfinder, you're looking with the least depth-of-field.

Yet, when you press the shutter release, the photograph may taken at f/16, especially if you're out in the sun.

There'll be lots of depth-of-field.

That difference in depth-of-field can create visual havoc.

An ugly background will not attract your attention in the viewfinder—because it's blurry at f/4.

But, if your camera takes the picture at f/16, the ugly background will be obvious in the photograph.

Become aware of what f/stop you're using, and use the depth-of-field preview button.

How to Set the Aperture

For Depth-of-Field

Use the A or Av setting on your exposure mode dial.

This setting allows you to set the aperture, while the camera sets the shutter speed for you.

Use f/4, say, for very little depth-of-field.

Use f/22, and thereabouts, for more depth-of-field.

For more depth-of-field, you can also use the flower icon setting on the exposure mode dial.

When set at this icon, the camera will use the smallest possible aperture for more depth-of-field, such as f/22.

For less depth-of-field, when doing a portrait, use the face icon setting on the exposure mode dial.

The camera will select the largest possible aperture, such as f/4.

Sometimes, You Can't

Do What You Want

You need lots of light when the aperture is set at f/22 for more depth-of-field.

If there's too little light, you're camera will blink Lo.

Likewise, if you want very little depth-of-field, you need an aperture that's physically big, such as f/4.

If you're in Death Valley at noon, too much light will be coming through the lens at f/4.

You're camera will blink Hi.

You can switch to a different ISO setting.

You can also block unneeded light with a Polarizing filter or a neutral density filter.

Distance

As discussed, depth-of-field is determined by aperture.

It's also determined by how far away you are from the subject.

For example, if your subject is more than, say, fifteen feet away, you will see no difference in depth-of-field at different apertures.

However, depth-of-field becomes increasingly important as the subject gets closer to the camera.

Learn More

Lens Opening

Depth-of-field