Depth of field

No camera, however sophisticated, will always see what the eye sees. Nothing illustrates this better than depth of field. In simple terms, depth of field means what's in focus in an image and what isn't. A more precise definition is that depth of field is the zone—extending both before and behind the point of focus —in which objects appear to be sharp.

The human eye scans the world dynamically. Whatever we're looking at, near or far, normally appears

Depth of field preview

When you look through the DSOOO's

viewfinder, the lens is set at its

widest aperture; if a smaller aperture

is selected, it will stop down at the

moment the picture is actually taken.

This means that what you see in the

viewfinder may have much less depth

of field than the final image.

Unlike Nikon's professional DSLRs, the

D3000 does not have a depth-of-field

preview button. This was essential on

35mm SLRs: pressing the button stops

the lens down to the selected aperture,

giving a sense of the depth of field in

in focus (assuming you have good eyesight, or appropriate glasses or contact lenses). This gives us a sense that everything is in focus, which photographs often fail to match. In landscape photography it is traditional to emulate this all-in-focus view of the world by maximizing depth of field. However, we can choose to take a different approach—creative intent or necessity may lead us to take photos with much narrower depth of field.

the final image. Unfortunately, it also

darkens the viewfinder image. With

digital SLRs there is an alternative,

whenever time allows, by taking a

test shot and checking images on

the monitor, perhaps zooming in

for a closer look. We could call it

depth-of-field review. This can give

a better sense of depth of field than

the preview button ever did, but it is

significantly slower. Still, many people

would argue that it's good to slow

down and take a little more time—

even just a few seconds—to think

about what you're doing.

114 NIKON D3000

Three main factors determine depth of field: the focal length of the lens, the aperture, and the distance to the subject. Because focal length and subject distance are often determined by other factors, aperture is key. The simple rule is small aperture = big depth of field, and vice versa.

Remember that aperture numbers are really fractions, so f/16 is a small aperture, while f/4 is large. The Nikon DSOOO's Information Display, when set to Graphic format, includes an illustration corresponding to the lens aperture (see page 33).

Long lenses (telephotos) produce less depth of field than wide-angles. To increase depth of field, then, you would naturally think of fitting a wide-angle lens. However, this changes other elements too, making the situation more complex. For example, suppose your main subject is a tree. To make sure that every branch and t̂ vig is sharp you need good depth of field, so you might fit a wide-angle lens. Then, however, you have to move in closer to keep

DEPTH OF FIELD The same setup, focused on the near edge of the toothed cogwheel, taken at f/2.8, f/8, and f/22, shows the effect on depth of field. Which version you prefer is, of course, subjective.

THE EXPANDED GUIDE 115

the tree the same size in the frame— and moving closer reduces depth of field, losing at least some of the benefits of the change of lens.

Moving closer will change your perspective and the apparent shape of the subject. And if you're shooting a broad landscape, rather than a single tree, you may already have decided on the viewpoint and angle you want, so changing the lens may not be an option anyway.

Apparent sharpness The definition of depth of field refers to objects appearing to'be sharp. In a small image, subjects may appear sharp but begin to look fuzzy when the image is enlarged. Depth of field is a relative value rather than an absolute. It's easy to forget this and become obsessed with using the smallest apertures and determining the hyperfocal distance. All this may be overkill unless you are planning

Hyperfocal distance

When you really need an image to

be sharp throughout, remember

that depth of field extends both in

front of and behind the point of

exact focus. If you focus at infinity,

there's nothing beyond that, so

you are in effect wasting half your

depth of field. In fact, depth of field

extends to a greater depth behind

the point of focus than in front of it.

To exploit this, you'll frequently see

advice to "focus one-third of the

way into the picture," although this

doesn't really help: what's one-third

of the way from here to infinity? This

is clumsy shorthand for focusing

at the hyperfocal distance.

The hyperfocal distance is the point

on which you need to focus in order to

ensure that depth of field extends to

infinity. It is not a fixed distance, but

varies with focal length and aperture.

There are tables and calculators you can

use to work it out, but there are also

rough and ready ways to establish

hyperfocal distance in the field. One

simple method goes like this: start by

focusing on infinity—in practice, the

most distant object in the scene. Play

back the image and locate the nearest

objects that appear sharp: they are at the

hyperfocal point. Refocus at this distance

for maximum depth of field. Remember

that if you change the aperture, the

hyperfocal distance also changes.

116 NIKON D3000

SCHATZALP, DAVOS, SWITZERLAND I wanted everything from the nearest foliage to the distant peaks to be sharp, and focusing at the hyperfocal distance helped make it so.

Note Nikon's documentation is not

entirely clear, but it looks as if the

DSOOO's Landscape mode uses the

hyperfocal principle, or something

like it, to keep both foreground

and background in focus as far as

possible. However, it clearly does

not always set the smallest possible

aperture; for full control over this,

use (A) Aperture priority mode.

THE EXPANDED GUIDE

to make big prints or submit your images for magazine reproduction. A quick full-screen review on the LCD monitor is often all that's needed, and certainly one or two presses on the ® button is sufficient to check sharpness and depth of field for images which will be printed small or viewed on screen.

For various reasons, images shot with the D3000, or any DX format camera, will have greater depth of field than comparable images shot on a 35mm or "full-frame" camera. This gain is only partly offset by the extra enlargement needed in printing.

117

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There is a point near the camera at which objects come into focus. The measurement from this point, all the way to the point where things begin to fall out of focus (some­times infinitely far away) is known as a shot's depth of field.

Depth of field (d.o.f.) is determined by lens-type, the aperture setting that has been selected, and how far away the subject is. Some lens/aper­ture combinations result in a shal­low d.o.f.—others deep. The d.o.f. of most advanced digital cameras can be manually controlled (the degree to which depends on the lens that is being used). Control over d.o.f. is a good reason to consider upgrading to something more advanced once you've gotten a handle on the basics (few pocket digi-cams offer more than inciden­tal control over their d.o.f.).

The samples on this spread provide a simple demonstration of the effects of manually adjusting the d.o.f. while taking a series of shots.

Look at photos in galleries, maga­zines, advertisements and web sites. Notice how a shallow depth of field is often used to confine the focus to certain essentials. Look for samples of a deep d.o.f. as well. Take note of which effect seems to work best in support of what type of message and stylistic result.

These samples demon­

strate how changing a

camera's depth of field

affects its view of a

scene.

In technical terms, the

"f-stop" number (dis­

played to the right of

the images, opposite)

reveals how far open

the camera's aperture*

was manually set for

each shot The lower

the number, the wider

the aperture opening,

and

the shallower the

depth of field.

Conversely, reducing

the aperture opening

(represented by a

higher f-stop number)

increases the lens's

depth of field. This nar­

rower aperture opening

also means that the

amount of light getting

to the camera's image-

sensor is reduced.

Therefore, when shoot­

ing with a deep d.o.f.,

more light

or longer exposures

may be needed to

properly capture

the image.

*The adjustable

iris-like opening inside

the lens.

307

F2.8

The photos on this

page were each

taken using a digi­

tal SLR fitted with

a 100mm macro

lens. Changes to

depth of field affect

different types of

lenses to varying

degrees, SEE LENSES,

PAGE 322.

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F32

308 DEPTH OF FIELD

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Another depth of field demonstra­tion: this one con­ducted outdoors.

Digital cameras make ideal photo­

graphic learning tools since you can review your images

on the spot and make adjustments to your technique

accordingly.

The lens is focused on the grass in the •

foreground using a shallow depth of field.

As a result, the lighthouse in the back­

ground is a barely distinguishable blur.

Here, the d.o.f. has been increased. More

of the grass in the foreground has been

brought into focus and the lighthouse is

now recognizable. This shot is a fairly good

representation of the way the human eye

would view the scene.

Here, the camera's primary focus is still on

the grass, and the lens' maximum d.o.f. can

almost, but not quite, bring the lighthouse

into focus. Note: If I had wanted a shot

where everything was in sharp focus, I

could have moved the camera back a few

feet so that the grass in the foreground was

not so near to the camera's lens.

The f-stop setting used for this image

is the same as it was for the above

example. The only difference is that

the primary focus is now on the light­

house rather than the grass. Using a

camera with manual depth of field

control puts a great deal of artistic con­

trol in the hands of the photographer.

•

309

F2.8

The photos on this

page were each taken

using a digital StR fit­

ted with a

70-300mm

telephoto lens.

SEE LENSES, PAGE 322,

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