Minimize Depth of Field for Selective Focus

A lot of depth of field is a great thing if you want everything in your pictures to be in sharp focus. But there are times when you might want to limit or restrict depth of field so that only your main subject is sharply focused and the background and/or foreground is less sharp. The main reason for doing this is to accent your primary subject--in a head-and-shoulders portrait, for example--where you want your subject's face in sharp focus but want to toss the background into a soft blur.

You can reduce the amount of depth of field by simply reversing the things we talked about in the previous tip. Again, here are the primary factors:

• Lens focal length: The longer the focal length of the lens, the less depth of field you will have at any given aperture (f/stop) and at any given distance. As you zoom a lens from wide to telephoto, for example, you quickly lose depth of field (provided you are keeping the aperture the same, see below). I used a 70-300mm Nikkor AFS lens at the 300mm position (450mm in 35mm terms) to shoot this horse on the King Ranch in Kingsville, Texas partly because I needed the long lens to bring the wild horse close, but also so that I could throw the foreground scrub and background out of focus.
• Lens aperture: The wider the aperture (again, assuming focal length and subject distance are constant) the less depth of field. You will get significantly less depth of field at f/4 than at f/16, for example. Think "smaller" f/stop numbers = larger lens openings = less depth of field. Remember, this does not affect how sharp your subject will be if you focus carefully, the larger aperture only reduces the near-to-far sharpness.
• Subject distance: The closer you are to your main subject, the less that will be in sharp focus in front of and behind the subject. Want less depth of field? Move closer. Want more? Get farther away from your subject.
  

So, if you were shooting a portrait of a friend sitting on a bench near a harbor and just wanted the person sharply focused with the boats in the background recorded as a soft impressionistic blur, you could choose a wide aperture and a long lens. You'll be able to see the results of your depth of field experiments on the LCD when reviewing the shot, but you won't see them if you're composing on the shot live on the LCD because the lens is not stopped down to its shooting aperture until you actually shoot the photo. (If you're using a DSLR with a depth-of-field preview button, you can use that feature to check it, but the viewfinder gets so dark that it's often hard to tell the difference.)

Keep in mind, if you're shooting with a point-and-shoot camera, you'll have less control when it comes to restricting depth of field because they tend to have inherently smaller apertures which (you knew this already!) creates more depth of field.

Finally, if you're shooting in bright light and the camera won't allow you to use a wide aperture, even at a high shutter speed, you can use a neutral-density filter in front of the lens to reduce the light. These filters won't affect color but reduce the amount of light entering the lens. I'll write a tip of "ND" filters in the future.

Focus Selectively

While there are many photo situations, such as a landscape, where you goal is to make the entire frame sharp, there are other times when you might want to limit focus to a very shallow area of the frame. This technique is called selective focus and it requires restricting what is called the depth of field, or the near-to-far area in a frame that is in acceptably-sharp focus. Selective focus is particularly useful in outdoor portraits (human or animal) because it enables you to subdue distracting backgrounds and focus attention on just your subject. In this shot of a wild horse that I photographed on the King Ranch in Kingsville, Texas, I used the technique to "pull" the horse out of somewhat distracting surroundings.

There are three primary things that affect how much will be sharp: aperture, focal length and your distance to the subject. All other things being equal, using a wider aperture (f/5.6 instead of f/11, for example) will create a much more shallow depth of field. Longer focal length lenses also limit sharp focus. In order to separate this horse from the dense underbrush, for example, I combined using a long (300mm) lens and a wide (f/5.6) lens aperture to limit sharp focus to just the horse. Also, because I was relatively close to the horse, the depth of field was even more shallow.

Depth of field is not as complex or scary as most books make it sound. Just remember that to limit depth to a narrow zone, use a wider aperture, a lens with a relatively long focal length (longer than normal, at least) and get as close to your subject as you can. For a very thorough look at depth of field, check out my book Exposure Photo Workshop.