You see Depth of Field mentioned a lot in magazine articles, books and on websites, but do you really understand what we mean by 'DOF'?
The nearer the subject is that the lens is focused on, the shallower the depth of field (DOF). Anything nearer or farther away than the area defined by the depth of field will appear blurry in the final picture. There are several factors that affect depth of field; so here's a quick list of what you need to know;
[1] DOF is significantly greater with compact digital cameras than any film camera
[2] DOF gets shallower the longer the lens in use; with a wideangle virtually everything is in focus, with a telephoto much less
[3] DOF also gets shallower the nearer the subject the lens is focused on. Subjects 5cm away may only have a DOF of a few millimetres, at 30 feet everything from a few feet to infinity will be sharp
[4] Finally, DOF is affected by the lens aperture setting... the smaller the aperture (bigger the F number) the more the depth of field.
For most scenic shots you want the maximum depth of field, so everything is in focus. This usually means a wide lens, fairly small aperture and distant focus point. But there are times when you want shallow depth of field – either to add emphasis to the main subject of the image or to remove a distracting background from a portrait. As mentioned at the top, digital cameras have a lot of depth of field anyway, so it can be a challenge to reduce it significantly. Use the long end of the zoom and portrait mode (or aperture priority) to set the widest possible aperture (low F number) and you should be able to throw the background out of focus.
