Depth of Field

Depth of Field (or DOF) is the amount of a picture that is in focus.

A picture where only part of the subject is in focus is said to have a “narrow depth of field”. This technique can be used to draw attention to a specific detail of a subject or to separate the subject from an otherwise distracting background.

This is an example of shallow depth of field. The frog is in focus but the background is not. This helps focus the viewer’s attention on the intended subject.

Typically a large depth of field is used for landscape scenes or any image where objects at varying distances from the camera need to be in focus.

Depth of field is affected by three factors.

1. Lens aperture 2. Distance to the subject 3. Focal length

Larger lens apertures (represented by smaller f-stop numbers) will give a smaller depth of field. Smaller apertures give a larger depth of field and will cause more of the picture to be in focus. The most extreme example of this would be a pin-hole camera which can produce images where almost everything is in focus regardless of how far it is from the camera.

Distance to the subject also affects depth of field. The closer you are to your subject the more pronounced will be the effect of your aperture. So using a large aperture at very close range will give you an extremely small depth of field - sometimes of the order of milimetres on a good quality lens.

The longer the focal length, the narrower the depth of field.

Point and shoot cameras often have difficulty reproducing small depth of field due to their small focal lengths. This is usually a benefit because it means that more of your picture will be in focus. Achieving shallow depth of field with a point and shoot usually means getting very close to your subject.