Ever wondered why some backgrounds are pin-sharp and others are out of focus? This is what’s called deep depth of field and shallow depth of field. Find out how to take full control of this in-camera photography effect and answer any of the common photography questions you may have.
Common questions about shallow and deep depth of field
What’s depth of field all about?
Depth of field is a measure of how much of a picture is in focus. A lens can only precisely focus on one plane at a time. However, there’s always a certain amount of the picture in front of, and behind, this plane that also appears to be sharp.
It is this zone of ‘acceptable sharpness’ that is the depth of field. Anything outside of this zone appears blurred or out of focus. The amount of depth of field varies from picture to picture, depending on a number of different factors.
How does knowing this help to improve my shots?
Depth of field is one of the most important creative controls available to the photographer. By learning how to control it, you can ensure that everything from your feet to the horizon appears pin sharp.
Alternatively, you can make sure that depth of field is restricted to such an extent that parts of your picture are thrown anonymously out of focus, for artistic effect or to hide distracting features in a scene.
So what’s the dark secret, then?
It’s not just one factor that affects the amount of depth of field that you end up with, but several working in tandem. Some of these factors, however, are much easier for photographers to control than the others.
What’s the easiest way to control depth of field?
The aperture setting you use is the simplest and most straightforward way of altering depth of field because you can do this without changing equipment or shooting position.
The smaller the aperture you set, the more depth of field you get and the more of your shot appears in focus. So on a typical zoom, a narrow aperture of f/22 will keep more of the shot in focus than a wider aperture of f/5.6.
The aperture can easily be altered by the photographer in a number of exposure modes, including Shutter Priority and Aperture Priority.
So I can set the depth of field precisely for every shot?
Yes and no. You can increase and decrease the amount of depth of field by adjusting the aperture. However, you don’t always have a free choice, because changing the aperture will affect the shutter speed, and some shutter speeds will not suit every situation.
Slow shutter speeds will cause moving subjects to appear blurred, for instance, or will create visible camera shake. More importantly, you only have a limited range of apertures, so often you can’t set the zone of sharpness precisely to suit your needs. But using the other factors can give you more control…
What are these other factors?
The two most significant factors are the focal length and the focused distance. The wider the angle of view of the lens, and the shorter the corresponding focal length, the more depth of field you get.
A wide-angle lens setting, therefore, gives you more depth of field than a telephoto one. The subject distance (or more accurately, the distance the lens is focused at) also has its role; the closer the focused distance, the less depth of field you get.
Is depth of field spread evenly in front of and behind the point you are focused on?
Almost never. In most normal situations, depth of field extends further behind the plane of focus than in front of it. Often the difference will be dramatic.
When shooting with a wide-angle lens and a small aperture, there will typically be a metre of depth of field your side of the focused point, but everything behind as far as the eye can see will also be sharp.
What about photographing macro subjects?
Depth of field at very close distances is evenly spread in front of and behind the focus point (but perhaps just a millimetre or two in each direction).
So what do I have to do to maximise my area of focus for deep depth of field?
First, set a narrow aperture (such as f/22). It may be necessary to use a tripod, or to increase the ISO to make small apertures feasible in anything but bright light.
Next, use the widest lens you can get away with for the subject, and stand as far away as possible. Finally, focus on a point about a third of the way up the frame to ensure as much of the shot as possible is sharp.
And what do I have to do to minimise depth of field and to maximise blur?
Use the longest lens you can get away with, and/or get as close to the subject as possible. Now set the maximum aperture available on your lens.
‘Fast’ lenses with wider-than-average maximum apertures are much better at this effect. Cameras that come with larger sensors also offer more restricted depth of field than those with smaller sensors.
In other words, all DSLRs are better than point-and-shoot digital cameras, but full-frame DSLRs are better than budget-priced DSLRs.
Learning the lingo around depth of field
Depth of field
A measure of how much of a picture is in focus, from the nearest point in the scene to the camera that looks sharp, to the furthermost point that looks sharp.
Depth of Field Preview
A feature on some cameras that enables you to see the viewfinder image at the actual aperture you’ll be using for the exposure. This will give you a visual indication of how much depth of field there is.
Circle of confusion
A point on a subject only appears as a point on the image if it’s perfectly in focus. If it is not, the point appears as a circle in the picture. The more blurred the picture, the bigger the circle.
If the circles are small enough, however, that part of the picture will still look sharp. The largest-sized disk that looks like a point is known as the ‘least circle of confusion’; this scientific measurement is fundamental to accurate calculation of depth of field.
Optical term to describe objects so far away that light from them reaches the lens as parallel rays. It is generally used to describe objects that are on or near the horizon.