Understanding Depth of Field

How your image looks and feels depends a lot on one of the most important elements of photography, and this is depth of field (DoF). Many of today’s photographers that alternate from using a digital SLR camera to a simple point-and-shoot tend to overlook this very important aspect in photography. The more recent models and range of cameras out in the market and almost all of the ultra zooms have remarkable control on depth of field, but not all photographers utilize the full extent of this feature.

Depth of field is simply defined as the distance or depth from a certain point that a photograph will be sharp to where the rest of the background in the shot is blurry. A broad or extensive depth of field will have a larger portion of your image clearer or in focus. A narrower or lesser depth of field will make more of the area look out of focus. This is not a sudden transition from sharp to blurry, but rather it is a gradual change:

Notice in this pebble image that the foreground and the background are gradually getting more blurred the further away they are from the middle ground which is the focal point, which is the area that is the sharpest and most clear.

Both techniques can create polar effects that can add to the impact of your shot depending on what effect you want to create. The use of narrow or broad depth of field is a type of approach the photographer can use to keep attention on the focal point or to create artistic impressions.

Four main factors contribute in controlling depth of field;

1.) Aperture Control – the lens aperture directly affects depth of field. Big apertures (small f/numbers) result in a narrow or shallow depth of field while smaller apertures (large f/numbers) result in a broader depth of field. To draw a viewer’s attention more to the subject, create an effect that blurs the background (more commonly known as selective focus) by using f/numbers such as f/2.8 or f/4. To have a clear and focused shot without the blurring effect, use f/numbers such as f/16 or f/22.

2.) Focal Length – When parallel light rays enter a lens that is focused at infinity, they converge to a point called the focal point. Focal length would be the distance from the middle of the lens to the focal point. The three main types of lenses, namely wide-angle, telephoto, and normal lens, can be described by their focal lengths. More info can be found in the article Explaining the Various Camera Lens Types.

3.) Subject Distance – the closer the camera is to the focal point or the subject, the less available depth of field.

4.) Sensor Size – the smaller the sensor size, the greater the depth of field. They are organized by their crop factor, which uses the frame of a 35mm film as a comparison.

The sensor is already set to a standard function, so it can’t be altered. The focal length and distance from your subject is largely reliant on what type of composition will be used in the photograph. The lens aperture then primarily controls the depth of field.

For more information on the relationship between aperture and DoF, check out our article, Aperture and Its Impact on Depth of Field.