Even when you break it down to the simplest terms, the relationship between aperture and depth of field can seem confusing. Whenever I teach a class, or try to explain the manual settings on a friend's camera, this is the always topic we have to go over again and again. The good news is that with practice and concentration, the aperture/depth of field relationship will finally 'click' for you. The bad news is, there is more to understanding depth of field than just using your aperture.

But let's get back to basics. What is depth of field?

In simple terms, the depth of field is the area behind and in front of your main point of focus, that is also acceptably in focus. So if you focus on a subject one metre away, you might look at your photo and find that everything from 0.9 to 1.2 metres is in focus. In this case, your depth of field is 0.3 metres (30 centimetres).

The very first thing a new photographer learns about depth of field is that it is controlled by the aperture on your lens. Very simply, a smaller aperture creates a larger depth of field, and a larger aperture creates a narrower depth of field. So if we go back to our previous example, let's say the 30cm depth of field was captured with an aperture of F-8. You could narrow the depth of field considerably by adjusting the aperture to F-2.8, a much wider setting.

Sound confusing? It is hard to explain it any more simply, especially without showing you photos as examples. If this is your first time working with depth of field, don't worry. Go outside right now and take some shots just as I have described, and you should be able to see the results right away.

So if it is that simple, why do so many people struggle with depth of field? As I wrote earlier, there is more to depth of field than just the aperture.

Depth of field is also affected by how close the subject appears in your photo. That means either how close you are to the subject, or how much you magnify or reduce the subject using different sized lenses.

The closer you are to your subject, or the closer you make the subject appear by zooming in with your lens, the smaller the depth of field becomes. Let's say you are photographing a person five metres away. At this distance, a standard or wide-angle lens will not only show a lot of background, but the wide depth of field could make the background quite distracting. However, if you walk much closer to the subject and re-focus, the depth of field will become much smaller. As a result, the well-focused person will stand out clearly from a blurry background. You can maximize the effect by opening the aperture to its widest setting.

Now imagine your subject is posing in front of a beautiful waterfall. If you stand close to the subject and photograph them with a wide aperture, you could get a great shot of the person but the waterfall will be an out of focus blur. You could improve the situation slightly by closing the aperture a few stops. However, the most effective way to improve the depth of field is to stand a few metres further back, and/or zoom back to a wider angle with your lens. Not only will more background be visible, it will also be sharper (thanks to the increased depth of field) than if you adjusted the aperture alone.

So there you have a quick look at not one, but three factors than can make it easier to master depth of field; aperture, distance from the subject, and the size of the lens. This really is a topic that needs to be illustrated with a few photos, but hey - you have a digital camera. Why not go and try out these ideas at the next opportunity? It won't cost you anything, and you can see the results right away. With practice and patience, you will get a 'feel' for depth of field, and how to use it to improve your photography.