Sometimes a photo only focuses on the subject and everything behind and in front of it is out of focus. Other times, things behind and in front of the subject are also in focus. You can see two examples below.
In the picture on the left you can see that not only the cat (our subject for this photo) is in focus, but also the table, the fruit, the curtain, and so on. This is called having a deep depth of field. Now, the picture on the right is focused only on the cat. Everything else is out of focus. This is called having a shallow depth of field.
So which is better? The answer is sometimes one sometimes the other. Landscapes are usually taken with a deep depth of field, so that you get the feeling that you are staring deep into the photo (like a nice painting). On the other hand, when you take photos of things close up (including the cat above), you might want the picture to just highlight your subject. Most people would agree that the photo of the cat on the right is better than the one on the left.
So how does depth of field (DOF) work? It is the distance between the nearest and farthest points in a photograph which are in focus. Depth of field is mainly controlled by making the hole through which light enters the camera bigger or smaller; this hole is called the aperture.
The bigger the aperture the shallower the depth of field. Some cameras let you control this; other cheaper ones do not. The aperture control is called f-stop. Just remember, the larger the f-stop number, the smaller the aperture. So, to get a shallow depth of field you need a small f-stop number and to get a deep depth of field you need a large f-stop number.
You can also affect depth of field by how far or close you are to the subject (the farther you are, the shallower the depth of field) and different lenses also affect how the picture comes out.
Try experiment with your camera and equipment to see what kind of pictures you can take.
by Simon James Allanach, edited by Alan Frost
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