Selective Focus Technique

A detailed image of sunlit flowers in the grounds of the Palace of Versailles, France.

Selective Focus is a great technique that helps you ensure you're able to direct the viewer to the primary focal point (e.g., subject) within the frame, rather than to similar elements which might otherwise compete for their attention. I made the above photo, to demonstrate this technique, in the gardens of Versailles on a warm summer day. Let's look at how to apply the selective focus technique to your images.

  • Ensure the lens is focused on your primary focal point. You can employ focus peeking, where possible, to achieve more critical focus.
  • Employ a shallow depth of field to de-emphasize the surroundings and, thereby, make your primary focal point stand out against a de-focused background.

Achieving a Shallow Depth of Field

Folks often complain to me that they're unable to blur the surroundings to the degree they'd like to. The reasons for this are a little complex, although the solution is, sometimes, quite straightforward. Let's work through the three factors that determine depth of field.

Aperture

  • A physically wide aperture, such as f3.5 (or wider), will produce a relatively shallow depth of field
  • A narrow aperture, such as f22, will produce a large depth of field

Lens Focal Length

A wide-angle lens (e.g. 18mm) will produce a larger depth of field, at a given aperture, than a more powerful focal length (e.g. 55mm) would at the same aperture and camera to subject distance.

Camera to Subject Distance

The closer you get to your subject the more quickly the surroundings (i.e., foreground and background) will fall out of focus. Conversely, moving further away from your subject will increase the depth of field.

One of the problems folks have achieving a shallow depth of field is due to the fact that the lens they use (probably a kit lens) does not have a particularly wide maximum aperture. Whilst f3.5 is relatively wide, apertures of f2.8, f2 or f1.4 will produce significantly shallower depth of field.

Furthermore, the maximum aperture associated with most kit lenses varies with the focal length. As you zoom in, to bring the subject or scene closer, you loose the ability to gather light. As a result the lenses maximum aperture is reduced from, for example, f3.5 to f5.6. While zooming in should, in theory, create a more shallow depth of field the resulting loss of maximum aperture, from f3.5 to f5.6, will likely mitigate that from occurring.

In such case you're probably best just moving in closer. It's a great solution which, to all intensive purposes, appears non-technical. And who wouldn't like that.

Glenn Guy, Travel Photography Guru