Depth of Field

Whenever you take a picture, an area extending in front of and behind the point which you actually focus upon will also come out sharp in the image. This area is known as 'depth of field', and it is one of the most important variables in photography, because it allows you to control what will be in- and out-of-focus in your pictures.

There are three basic factors that determine how much - or how little - depth-of-field there will be in a photograph, as follows.

1. The aperture set on the lens

The smaller the lens aperture (the bigger the f/ number), the greater the depth-of-field, and vice versa, for any given lens.

2. The focal length of that lens

The shorter then focal length (the wider the lens), the greater the depth-of-field is at any given aperture.

3. The focusing distance

The further away the main point of focus is from the camera, the greater the depth-of-field will be for any given lens and aperture setting.

Maximising depth-of-field

If you want to achieve maximum depth-of-field so that everything is recorded in sharp focus from the immediate foreground to infinity - which is normal when shooting landscapes - use a wide-angled lens such as 28mm or 24mm and set it to a small aperture such as f/16 or f/22.

Remember that the smaller the aperture is, the slower the shutter speed will be and the risk of camera shake is increased - so try to keep your aperture as large as possible at all times. Ideally you should also focus your lens roughly a 1/3rd into the scene, as this will help accentuate the sense of depth-of-field in the image.

Minimising depth-of-field

If you want minimal depth-of-field - which would result in little more than the main point you have focused on coming out sharp and everything else in the image being thrown out-of-focus - use a telephoto lens in the range of say 200mm to 300mm set to a wide aperture such as f/4 or f/5.6.

This is common practice with subjects like portraits, candids and sports action, in which you want the background to be out-of-focus so that it does not compete with your main subject.

Minimising depth-of-field also creates a strong three-dimensional feel, as it makes the main subject stand out in the image.