Aperture and Its Impact on Depth of Field

One of the three elements that control image exposure is aperture. Aperture is the size of your lens opening as the shot is being taken. When the shutter release is pressed, the aperture would be the size of the hole where the light passes. While shutter speed is measured by time, aperture is measured by size, called an f-stop. If you notice, the bigger the lens hole, the smaller the f/stop number. For example, an f/2.7 setting has a larger lens opening compared to an f/8. This may seem confusing at first but you will get soon get the hang of it.

Aperture has a direct impact on depth of field (DoF). When you change the aperture setting, the span of area that is in focus also changes. The bigger the f/stop, the larger the depth of field, and the more light you will need to illuminate the subject, and vice versa.

When shooting landscapes, you might want to have as much of the scene in focus, if possible. You would need a large aperture to get a bigger DoF. On the other hand, if you shooting close up or macro photos, a shallower DoF will keep a specific part of the subject in detail while blurring the rest of the background.

Here is a simple photo comparison:


Photo 1 was shot using an aperture of f/2.7 which provided a large lens opening (which let in more light). Shutter speed was at 1/40s. The tomato at the foreground is clear while the two in the background are blurred. Photo 2 had an aperture of f/8 which allowed for a larger DoF but less light to be captured. I had to compensate with the shutter speed which I adjusted to 1/8s.

One way to learn when to use certain aperture sizes is to let your camera teach you. Most digital cameras have a built in light meter that will suggest what settings to use based on the light being reflected on the scene. Use the given aperture size as a guide if you want to override and adjust the exposure settings manually.

When you are completely familiar with the aperture setting and know when to use a particular f/stop in relation with the shutter speed and ISO, when being aware of what impact each makes on depth of field has become second nature to you, then will you have control over how your image comes out and its intended effect.