photokaboom

Learn Photography

Beecher's Handouts >

16 – Depth-of-field

1 – Introduction

Depth-of-field is a valuable composition tool.

When you focus on your subject—that's where the focus is the sharpest.

However—there's a zone in front and behind the subject that's acceptably sharp.

This acceptably sharp zone is the depth-of-field.

Compare the two photographs below.

In each, the camera was focused on the crystal paper weight.

The top photograph has very little in focus.

The depth-of-field is shallow.

There's more in focus in the bottom photograph.

It has more depth-of-field.

q

Shallow Depth-of-field

q

Deep Depth-of-field

The amount in focus, the depth-of-field, depends on three factors.

1) Lens opening

2) Distance from the subject

3) Sensor size

We'll look at each of these factors.

2 – Lens Opening

In both photographs below, the camera was focused on the bottom edge of the book.

q

f/4.5

q

f/22

Note how the title is out-of-focus when the lens opening is at f/4.5.

Wide lens openings, such as f/4.5, have less depth-of-field.

Not as much is in focus.

The book is more in focus in the right photograph.

The small lens opening, f/22, has more depth-of-field.

Think Before You Press!

Learn to ask yourself if you want the background in focus or not.

A good way to ensure that you consider depth-of-field is to use aperture-priority exposure mode.

If you have to set the lens opening, you'll think about depth-of-field.

Frustration

You can't always use the lens opening that you would like to use.

Sometimes there's too little, or too much, light.

If this occurs, Lo or Hi will blink in your viewfinder, letting you know that you have to adjust the lens opening.

Let's look at another factor that determines depth-of-field.

3 – Distance from the Subject

Depth-of-field also depends on how close you are to the subject.

If you're more than, say, fifteen feet from your subject, different lens openings will have about the same amounts of depth-of-field.

As you get closer to the subject, depth-of-field becomes more evident.

As you get closer and closer, the depth-of-filed decreases.

In the photograph below, very little is in focus because of the wide lens opening, f/4.5.

And, the camera is close to the marigolds.

q

f/4.5

Click Photograph to Enlarge

In the next photograph, much more is in focus.

That's because the small lens opening, f/22, produced more depth-of-field.

q

f/22

Click Photograph to Enlarge

If you're close to your subject, consider using a small lens opening, such as f/22.

4 – Sensor Size

In addition to aperture and how close you are to your subject, the size of the sensor affects depth-of-field.

FX & DX Cameras

Full frame (FX) cameras have less depth-of-field than APS-C (DX) cameras.

Their sensors are bigger, hence, less depth-of-field.

That's good if you want to blur the background, such as a portrait.

That's bad if you're doing a close-up and need lots of depth-of-field.

Point-and-shoot Cameras

If you use a point-and-shoot camera, you can ignore the discussion about depth-of-field.

Your camera has a sensor that's very small.

Therefore, your camera has lots of depth-of-field—even at wide lens openings.

Having lots of depth-of-field is both good and bad.

The Good

The #1 complaint of photographers is unsharp photographs.

With lots of depth-of-field, your photographs will be sharp.

This is especially useful when doing close-up (macro) photography, where there is less depth-of-field because you're close to the subject.

The Bad

You're less able to blur the background behind the subject.

Why Does Sensor Size

Affect Depth-of-field?

Go to 4 – Depth-of-field & Sensor Size.

5 – How to Get Less

What do you do if you want less depth-of-field?

Use a 50mm film lens on your digital SLR or mirrorless camera.

The lens becomes about a 75mm lens on most cameras.

If you use a 50mm lens that has a aperture of f/1.4, you'll have three stops less depth-of-field than your zoom lens.

You can blur backgrounds more completely.

In the photograph of the grape leaf below, taken at f/4, note how the background is sharper than the photograph taken at f/1.4.

q

f/4

q

f/1.4

Caveat

When using a wide aperture like f/1.4, be sure to focus carefully.

6 – A Reason for Poor Backgrounds

This section applies to digital SLR cameras, not to mirrorless cameras.

One reason for poor backgrounds is the fact that when you're looking through your camera, the background is apt to be out-of-focus.

So, you don't pay much attention to the background.

Why is the background out-of-focus?

When you're looking through your viewfinder, the aperture is physically large.

The aperture stays wide open, until you press the shutter release.

With the lens wide open, you can see what you're photographing easily.

The aperture may be at f/4, for example.

Yet, when you press the shutter release, the aperture may be different.

If it's a sunny day, the photograph may be taken at f/22.

The background will be much sharper in the photograph than what you saw in the viewfinder.

For example, the photograph below is what was seen in the viewfinder.

The photograph further down is how the photograph looks.

Because it was a sunny day, the camera chose f/22 for the aperture.

Therefore, far more was in focus than what was seen in the viewfinder.

q

f/4.5

What Was Seen in the Viewfinder -

With Less Depth-of-field

Click Photograph to Enlarge

q

f/22

The Actual Photograph - With More Depth-of-field

Click Photograph to Enlarge

Solutions

Depth-of-field Preview Button

A few cameras have a depth-of-field preview button.

When you press the button, the lens opening moves from wide-open, say f/4.5, to where it will be when the shutter is released.

This feature is handy for judging depth-of-field.

When you press the button, the viewfinder may become quite dark.

You may not be able to see your subject clearly, but you can see the outline of the subject.

Press the button and release it, back and forth, to compare the depth-of-field.

DEP on Canon Cameras

Canon cameras have a feature called DEP which allows you to more easily adjust the aperture for more depth-of-field.

 7 – A Myth

There's a rule for depth-of-field that's set in stone.

The depth-of-field zone is 1/3 in front of the subject—and 2/3 behind the subject.

It's correct only at a few settings, however.

Don't use the myth.

Enter different values in the DOFMaster Online Depth of Field Calculator to see how the rule is wrong.

8 – Diffraction

When photographers first learn about depth-of-field, they often become small-aperture enthusiasts.

They use the smallest possible aperture—all of the time.

Their photographs may, unexpectedly, not be sharp.

While small lens openings have more depth-of-field, they also have more diffraction.

Diffraction degrades the sharpness of the photograph.

What's Diffraction?

Let's say you're photographing an apple.

Light reflects off of the apple, goes through the lens opening, and strikes the sensor.

However, some of the light waves also hit the edge of the lens opening.

These light waves reflect off in new directions.

The light waves coming directly from the apple are degraded by the waves that are coming from the edge of the lens opening.

The two sets of waves interact with each other, reinforcing and canceling each other.

This interaction degrades sharpness.

At large lens openings, the amount of the diffracted light is a small portion of the total amount of light reaching the sensor.

At small lens openings, the percentage of diffracted light increases.

How to Avoid Diffraction

For photographs that will be enlarged greatly, avoid using lens openings smaller than the focal length of the lens divided by four.

For example, let's say you're using a 50mm focal length.

50mm / 4 = 12.5

The closest lens opening to 12.5 is f/11.

Do not go smaller than f/11 when using a 50mm focal length, for optimum results.

Point-and-shoot Cameras

Point-and-shoot cameras often have f/8 as the smallest lens opening.

At a focal length of 6mm, the physical size of the lens opening at f/8 is .75mm.

.75mm is a tiny lens opening.

If the camera had smaller lens openings, such as f/11 and f/16, diffraction would become evident at these smaller lens openings.