As you further your skills in photography, you find yourself spending as much time concentrating on backgrounds as the subject itself. A background can compliment or detract from your central subject - it is up to you to take control.

Controlling the sharpness of the foreground and background in a photograph requires an understanding of a term known as ‘depth of field’. Depth of field is the actual depth of sharpness in a photograph extending from the foreground to the background. Simple non-adjustable cameras are designed to give you a very large depth of field where everything is in focus. For an amateur photographer, this is great and no thinking is required. However, the more critical photographer wants to have total control of the final image.

This control requires that you start working with cameras that are adjustable and have interchangeable lenses. In this article we will explain three ways to control depth of field and how you can consistently capture more exciting images. Also, keep in mind that the procedures outlined are easy to do.

The first way to control depth of field is by varying the camera-to-subject distance. The closer to your subject you get, the less your depth of field. In other words, your backgrounds and foregrounds get more and more blurry.

For example, if you were to take a vertical head and shoulders portrait of someone at a distance of one meter from your subject, you would not be able to have distant objects in the background appear in sharp focus. So, one very simple and inexpensive way to control your depth of field is to simply move close to your subject. Nothing complex about this. On the other hand, if you want a larger depth of field, you can accomplish this by moving further back. Have you ever seen a scenic picture taken with the foreground and background blurry? Probably not. When taking pictures of distant objects, everything is in focus.

The nice thing about moving close to your subject is that you not only control your depth of field, you also simplify your composition by eliminating a lot of unwanted details. One hard lesson to teach students is to get them to walk up to their subjects as they can be a little reserved and take pictures from too far away. Encourage them to move in closer and you will be impressed with the great improvement in composition.

Look at the two images to the right.

Image One was taken from about three meters away while Image Two below was taken from about 5 meters away. Note that the background in Image Two, although still a little blurry, is sharper than that in Image One.. A greater distance has increased the depth of field.

Okay, now on to the third way to control depth of field. If you have a camera that allows for the interchanging of lenses, you have even more control at your disposal. The most common film format is 35mm. Cameras that take this film format use a ‘normal’ lens that is usually about 50 mm. in length. The length may vary from 45 to 55 mm depending on the camera you are using. The length of the lens is normally written on the inner flange of the lens. Lenses that are shorter than 50mm are called wide-angle lenses while lenses longer than 50mm are called telephoto lenses. All you have to remember is that the longer the lens, the less your depth of field. For head-and-shoulder portraits and pictures of small groups, my favourite lens is 105mm. This lens gives you just a beautiful control of depth of field under these conditions. If you have a zoom lens, 80mm to 150mm is a great focal length range to work with in portraiture. The two pictures illustrating this article were taken with a 105mm lens. As you can see, this length coupled with an aperture of f/4 and short distances has resulted in excellent control of depth of field.

So, that’s it. Move in close, use a large lens opening, and attach a lens with a longer focal length. Combining all of these controls when taking pictures will give you dramatically improved images.

The next time you are taking pictures, experiment with the above suggestions and critically view your results. It doesn't do any harm to jot down a few notes when the pictures are taken so you don’t forget what you have done.

The second way to control depth of field is with the aperture found on the lens itself. The aperture controls the size of opening that light passes through when a picture is taken. Apertures have numbers like 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, and 22. The bigger the number, the less the light that enters the lens. When you move by one number, referred to as a one-stop change, you either double or half the light reaching the film. For example, if you move the aperture from f/8 to f/11, you half the light. Conversely, going from f/11 to f/8 would double the light. Oh, by the way, an aperture is usually expressed as “f/8’. The ‘f’ denotes a fraction of lens focal length divided by the diameter of the lens opening. Don’t worry about this technical detail.

What is important to understand is that large lens openings like f/2, f/2.8 and f/4 give a very small depth of field where foregrounds and backgrounds are blurry. What I like to do when I am taking a tight head-and-shoulder portrait of someone, is to simply open my lens up to the largest opening. Not only do you get great control of your depth of field, you also let in a lot more light and this requires a faster shutter speed to provide proper exposure on your film. The great thing about faster shutter speeds, is that if you or your subject move a little while the picture is being taken, blurriness of the subject resulting from motion will be minimized. Both pictures above were taken with an aperture opening of f/4, the largest opening on the lens used.