Aperture

We've been slowly moving away from "taking photographs" to "making photographs, what do I mean by this?

Moving from automatic settings to manual settings in order to create the photograph you want.
Together, shutter speed, aperture and ISO are called "the Exposure Triangle" and each affect the final photograph. You can choose to set only one of these at a time in different camera modes: "Aperture Priority Mode", "Shutter Priority Mode" and "Manual".
Exposure Triangle YouTube Video

What is aperture?

The aperture refers to the size of the opening in the lens through which the light enters the camera. The size of this opening can be adjusted and the aperture size is measured in f-stops. The image on the right shows you exactly what the aperture on a lens looks like.

When you change the f-stop value, you change the size of the opening. Here’s the weird thing though. The higher the f-stop, the smaller the opening.

Take a look at the chart below to see what different apertures look like at different f-stops. On the far left, you can see that setting an aperture of f16 will result in a small opening. Choosing an aperture of f1.4 will result in a very wide opening.

How does your choice of aperture affect the photograph?

The most noticeable effect your choice of aperture has on the photograph is the depth of field. What do we mean by this exactly? In very simple terms, depth of field refers to the amount of the image that is sharp. What does this mean in practice?

If you use a wide aperture, the depth of field will be shallow. Only part of the image is sharp and the rest will be out of focus or blurred. Look at the picture on the left below. The cat is perfectly sharp but the background is blurred. Using a wide aperture works well for portrait style photographs as it makes the subject of the shot really stand out against the blurred background.

In this case, the depth of field extends from about the tip of the cat’s nose to just behind its head, no more than a few centimeters (from point A to point B in the diagram). Anything not in this range, either in front of it or behind will not be sharp. For this shot, I used a wide aperture of f/3.5.

When you use a narrow aperture, the depth of field is deep. When the depth of field is deep, all of the photograph from foreground to background is sharp.

Take a look at the photo below taken in the Dublin Docklands. Everything from the dock cleat in the foreground to the bridge in the background is sharp. In this case the depth of field is several hundred metres, extending right from the foreground to the background of the scene. In this case, I used a narrower aperture of f/11.

Most of the time, we want to achieve a deep depth of field when shooting landscapes. We want all of the image to be pin sharp.

The mid range apertures (around f/8) are good for shooting handheld for example when doing street photography. You get a good balance between having enough depth of field and fast enough shutter speeds to shoot hand held. We’ll discuss shutter speeds in more detail later.

The chart below gives you a good idea how different apertures will affect the depth of field in your photographs. You can see that as the aperture gets wider, the pyramid in the background becomes more blurred.