This article is the first of a series dedicated to the concept of Depth of Field (DoF). It is a technically complex topic that scares many photographers including the experienced ones, and caries many popular misconceptions. The aim of these articles is to explain ‘how to control the DoF in your photographs’ in an understandable, but accurate way.

Essentially the articles will elaborate on the parameters that influence the DoF :
– Image format and viewing distance
– Aperture
– Focal length and distance to subject
– Sensor dimension or crop factor

But they will also provide useful  tips and tackle some popular misconceptions such as :
– DoF is not 1/3 in the front and 2/3 behind the focus point.
– Aperture is not the dominant parameter to control DoF.
– It is possible to make a group shot of 120 people with an aperture of f1.2 and have everyone in focus.
– A blurred background is not the same thing as a shallow DoF.
– It is possible to estimate the DoF at a glance.

Let’s start by recalling the definition of DoF from wikipedia :
”depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image” –  Wikipedia

A photograph is exactly sharp only on the focus plane, but it is still reasonably sharp within a certain distance around the focus plane. This distance defines the Depth of Field.

The graph below is plotted from the formula of DoF, it gives an idea of how the near and far limits of DoF varies with the distance to the subject. It puts in evidence that for a given aperture the DoF can be extremely small when focusing very close, or extremely large or even infinite when focusing far away.

It is also visible that DoF is not 1/3 in the front and 2/3 behind. It varies from 1/2 behind to infinity behind, the only certainty is that there is always more DoF behind than in front of the focus plane.

Now to further understand the DoF, we need to clarify what is an ”acceptable sharpness” ?  This will be the topic of the next article.