Here’s one of the first exercises I did that helped me understanding how
Aperture influences Depth of Field (DoF).

It’s true that adjusting the aperture changes the size of the opening in a lens letting in more or less light, but its side effect is an important tool that helps in composition. Take a look at the images below and see what happens as the f-value of the aperture increases (i.e as the aperture goes from wide to narrow). The background becomes sharper, right?

Click on the image to see it in a higher resolution.

How to set it up?

Grab your camera and place an object between you and the background. Set your camera on Aperture Priority mode, so you don’t have to worry about the shutter speed to get a good exposure.

How to do it?

Starting at your widest aperture (lowest f-value) possible, focus on any part of the object, frame your shot and shoot. Repeat the process with higher f-values (e.g. going up one f-stop on each photo).

How is this an advantage when applied to my photography?

Our eyes are drawn to what is in focus. So, by changing the Aperture you control the DoF in your image, which gives you the power to isolate your subject from the background or to keep everything in your image sharp. That way you lead people to look into your photograph the way you want. ;)

Hope it helps!