In this lesson: Discover how to limit your focus range with a wide aperture setting

Using a large aperture setting like f/2.8 or f/4 minimizes the depth of field of an image. The result is a subject that is in sharp focus, with a background that is nicely blurred.

Widening the aperture on your lens creates a shallower depth of field, also known as narrow focal range. Opening the aperture to a setting of f/5.6 or lower can create extremely shallow depth of field, giving you opportunities to isolate a subject with selective focus. Put simply, by focusing carefully on one element in the frame at a wide aperture setting, other elements will be left out of focus, drawing attention to the subject. This technique is commonly used in portraiture.

Look at the sample image above. Note how the little boy’s face is perfectly in focus. Then note how the background is blurry. This is what a shallow depth of field looks like. You can see how this technique brings additional focus to the subject – the sharpness of the boy’s eyes, for example, draws more attention than the soft, blurry background behind him.

In addition to enabling selective focusing, a wide aperture setting can have the following benefits:

• Allows for faster shutter speed settings in low light conditions: The larger the aperture you use, the more light that’s allowed into the lens. As a result of that added light, a faster shutter speed can be dialed in, even if you’re shooting at dusk or indoors.
• Allows for the creation of bokeh effects: The larger the aperture, the greater your ability to create bokeh, which refers to the quality of blur of the background. Note in the image above how the lights in the background are round, indicating a high-quality bokeh.
• Allows blurring of distracting backgrounds: As noted above, the wide apertures commonly used in portraits allow you to selectively focus on the subject while putting the background into blur. This minimizes distractions in the background while forcing the viewer’s eye toward the primary subject.

A Word About Exposure

Widening the aperture allows more light to enter the lens in the same amount of time. In order to maintain proper exposure, the shutter speed and/or ISO sensitivity will need to be adjusted accordingly. For example, if a scene will be correctly exposed at f/8 and 1/60 of a second at a given ISO setting, and you widen the aperture to f2.8, then you will need to set your shutter speed at 1/500 of a second or adjust both the ISO setting and shutter speed to achieve the same exposure.

Challenge Activity

This challenge activity will help you better understand the concept of using shallow depth of field as a method of drawing attention to a particular subject. As in the image above, your task is to find a scene in which there is a subject in the foreground that you can keep in sharp focus while blurring everything in the background.

Step 1: Position your camera very low in a field of grass or a scene of plants, as was done in the image above.

Step 2: Set your aperture to approximately f2.8 to maximize your ability to shoot with a shallow depth of field. Note that you will need to experiment with the shutter speed and/or ISO settings to ensure you get a well-exposed image.

Step 3: Focus on a single blade of grass, a leaf, or a flower, and take a photo. Then, repeat the same process, resetting the focus on a different element of the scene. After taking several exposures, compare the results in terms of how you were able to use aperture to selectively focus on different aspects of the same scene. Note that you can use this procedure to create blur in the foreground as well. Looking at the sample image above, notice how both the foreground and background are blurred, yet the boy remains in sharp focus. This is an ideal example of how selective focus can be used to draw more attention to your subject.