Depth of field and photojournalism

Depth of field is a holy grail for some, a mystery for others. A few keys to mastering it.

Photography is an artistic discipline in which physics plays a major role. Like any machine, a camera has characteristics governed by physical laws — and, with those characteristics, trade-offs. To photograph well you have to learn to play with those trade-offs. Depth of field is one of the characteristics with a direct visual impact on a photo. We're going to give you a few keys to managing your depth of field during a photo assignment — meaning, managing it quickly.

Definition of depth of field

First, a definition. Depth of field is the zone considered to be in focus. So it's a zone of sharpness on the image. To grasp depth of field properly, let's take a few lines to revisit, in simplified terms, what "sharpness" means. We can consider three broad families of blur in photography:

Camera shake: caused by the photographer's movement during the shot.
Motion blur: caused by movement of the subjects photographed.
Focus blur: linked to the focusing distance setting (manual or via autofocus).

For completeness, let's also mention diffraction blur, the last family. But we won't dwell on it. We'll only look at focusing here. Still keeping things simple and practical: the focusing distance is the distance between the camera and the subject. It's set automatically by your camera's autofocus, or manually (and often empirically) by turning the focus ring on your lens. So a subject at the focusing distance is in focus. But the focusing distance is a finite physical quantity. For example: your dog is 2.4 m from the camera, focus is set to 2.4 m, your dog is sharp. Except your dog isn't 0 cm or 0 mm thick. Yet your dog still looks sharp in the photo. He sits inside the zone of sharpness. That's an example of depth of field. The zone of sharpness extends in front of and behind the focusing distance, the blur increasing progressively before and after that distance. Depth of field is large (or even infinite) when the zone of sharpness is big, and small in the opposite case. The tricky thing about depth of field is that it depends on:

The focusing distance
The aperture
The focal length

To clear things up a bit, you can download .

Depth of field in reportage

Let's be plain: in reportage, depth of field has to be handled with care. Too shallow and it can play tricks on you if your AF points are misaligned; too deep and it often results in a flat-looking image. The particularity of reportage photography is that time is rarely on your side. Actions are fleeting, fast, and often unique. A focusing mistake or a too-shallow depth of field, and a successful — even brilliant — frame becomes a beautifully botched photo! It's therefore practically impossible to use a depth-of-field app or consult a depth-of-field table before shooting. So you have to store the rough orders of magnitude of depth of field in your head, based on the shooting parameters you use most often. To do this I regularly use the following workflow: 1/ For a given assignment, I review the best frames. 2/ I use a depth-of-field calculation app that works on both PC and Android, DoF (download links at the end of this post), to determine the depth of field. 3/ Depending on image quality and any imperfections, I deduce whether I worked at the smallest acceptable aperture or whether I should change it. This way, without knowing the exact depth-of-field value, I know when I can work at f/2.8, when it's a bit borderline, and so on. The advantage of DoF is that it offers the same interface on desktop and on smartphone. That gives you a single interface for the field and for cool-headed post-production work. Plus the interface is both numerical and graphical.

Depth of field — learn more

Rather than copy-paste Wikipedia, I encourage you to read the page on Depth of field and in particular the Theoretical Approach section. DoF Windows version DoF Android version