Friday Photography Tips #6 - Shallow Depth of Field

Musician Bobby Aherne - Thomas David Kavanagh

One of the most popular photography techniques, especially in portraiture, is creating a shallow depth-of-field. That is where only a small portion of the image is in focus, usually a person's face (most importantly their eyes!). The background of the image becomes blurry and dreamlike, lights that are some distance away from the subject appear like orbs - commonly referred to as 'bokeh'.

The image above is of the incredibly talented Iona Fyfe (MG ALBA Scots Singer of the Year 2018) accompanied by the wonderful Charlie Grey (Violin) and Luc McNally (Guitar). Captured from a balcony, this composition includes lights in the foreground that become 'bokeh' as the area of focus if much further away.

There are two ways of achieving a shallow depth of field in an image:

1. Focal Length

The Focal Length of a lens is measured in millimetres and in very simple terms describes the angle of view which the lens provides. Generally, focal lengths below 50mm are considered 'wide' and are likely to give you an angle of view greater than your eyes can naturally see - but also gives you a greater depth of field.

Focal lengths above 50mm are considered 'telephoto', showing a narrow angle of view and much like a telescope magnify whatever appears in the distance. Telephoto lenses also decrease the depth-of-field. The image above from a St. Patrick's day parade in Birmingham is taken at 200mm, focusing on a spectator in an oversized Leprechaun hat. The shallow area of focus means the background and foreground are out of focus.

Many standalone cameras offer a zoom lens (typically 18-55mm), zooming in with these lenses will decrease the depth-of-field.

2. Aperture

The aperture is an opening in the lens that determines how much light is let in. The smaller the F value is, the greater the aperture opening is and more light means more of it will be out of focus. Conversely, a high F value such as f16 means less light enters the lens but more of the image will be in focus - this is often used in landscape photography to capture detail in most of the scene.

The portrait above is taken at f1.4, creating a very shallow depth-of-field. Once more we see bokeh in the image, this time from Christmas lights in the background.

3. When to Avoid...

While this technique is very effective in capturing single subjects in isolation, it is best avoided when attempting to photograph multiple subjects or for environmental portraiture (where you want to show more of the subjects surroundings).

When photographing a group of people for example, unless everyone standing precisely in line it is likely one or more of the group will be out of focus. In such an event, try to use a wider focal length or a higher aperture value.