This issue, our expert at large explores why depth of field is so crucial, and how to use it more creatively
Michael Freeman takes an in-depth look at depth of field: how you can control it, and how to use it more creatively
As everyone knows, depth of field is defined as the range of distance in front of the camera in which everything looks
acceptably sharp. It can be deep, covering the entire scene, or it can be shallow, with only a narrow band sharp. It’s a term that we trundle out as if it explains everything there is to know about aperture, but ‘why’ is much more important than ‘what’.
And the reason why it needs explanation is that depth of field is a visual effect that we have very limited experience of with our own eyes. Healthy, adjusted eyes simply see everything as normally sharp. If you’re short-sighted or long-sighted (as more than a third of us are) then without glasses you’ll have some sense of blur, but it’s unlikely to come anywhere near the smooth blur in a selective-focus shot, or in almost any macro background. That’s why well-managed blur can be so appealing – it’s beyond our usual visual experience.
You change the depth of field by changing size of a lens’s aperture (see below). Depth of field does not change with focal length, but using a telephoto to magnify a small part of the scene gives the impression of shallower depth of field. With a wide-angle lens depth of field might be, say, a metre at f/4, so everything within a metre of your subject will be acceptably sharp; with a long lens, foreground and background are typically over a metre away from your subject, so will be blurred out.
At its most mechanical, depth of field is used to keep the important parts of a subject sharp, but there are many more interesting ways to use it to your advantage. You can use it to direct the viewer’s eye, but equally, by throwing some things unexpectedly out of focus, you can disrupt the viewer’s expectations. Using depth of field creatively means playing with the contrast between sharp and blurred areas.
Using depth of field creatively is a great way to direct the viewer’s eye to precisely what you want them to look at