The Exposure Trinity - The 3 Components of Exposure

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How to Control Aperture

Like shutter speed, aperture is one of two factors that determine how much light your camera's sensor is exposed to when you take a picture (exposure.) Controlling your aperture gives you more control over exposure and more control over how your image looks. The simplest way to begin experimenting with aperture is to put your camera in "aperture-priority" mode. To accomplish this, rotate your camera's control dial (indicated below) to "A" if you have a nikon camera like the D40 or "Av" if you have a canon camera.

In shutter priority mode, winding the command dial (indicated below) will change your shutter speed and your camera will do the rest of the work to produce a correct exposure. (If you have a camera with two control wheels, then the one on the front may control aperture in this mode.) As you peer through your viewfinder, you will see a number with an "f" in front of it changing as you wind. That number indicates your aperture. Remember that as that number gets larger, your aperture gets smaller.

Aperture and Depth of Field

While there are different reasons to take control of your lens' aperture, the most common reason to control your aperture is to affect the depth of field. Depth of field (DOF) refers to how much of your image appears sharp or in focus. Controlling DOF allows you to make background or foreground elements appear blurry to focus attention on your subject like this:

Most people are fond of the above affect, particularly for portraits. However, there are also times when you might want as much in focus as possible, like this:

Controlling aperture gives you the most direct control over DOF. Observe the differences in the following images.

This gives you a taste of what you can do with aperture. Will explore it more and talk about how to control it over the next few days.

What is Aperture?