Aperture is often the most difficult concept for people to grasp when they’re learning how their camera works, but it’s pretty simple once you understand it. If you look at your lens, you can see the opening where light comes through. When you adjust your aperture settings, you’ll see that opening get bigger and smaller. The larger the opening, or wider the aperture, the more light you let in with each exposure. The smaller the opening, or narrower the aperture, the less light you let in. Why would you ever want a narrow aperture if a wider one lets in more light? Aside from those situations where you have too much light and want to let less of it in, narrowing the aperture means more of the photograph will appear to be in focus. For example, a narrow aperture is great for landscapes. A wider aperture means less of the photograph will be in focus, which is something that’s generally visually pleasing and isn’t seen as a downside. If you’ve seen photographs with a subject in focus and beautiful blurred backgrounds, this is often the effect of a wide aperture (although that’s not the only contributing factor—remember, telephoto lenses decrease depth of field as well). Using a wide aperture is generally considered the best method for taking in more light because the downside—less of the photograph being in focus—is often a desired result.
Aperture is represented in f-stops. A lower number, like f/1.8, denotes a wider aperture, and a higher number, like f/22, denotes a narrower aperture. Lenses are often marked with their widest possible aperture. If you see a lens that is a 50mm f/1.8, this means it’s widest aperture is f/1.8. The aperture can always be set to be more narrow, but it won’t be able to go wider than f/1.8. Some lenses will have a range, such as f/3.5-5.6. You’ll see this on zoom lenses, and it means that when the lens is zoomed out to the widest position it’s f/3.5, but when it’s zoomed in all the way it can only have an aperture as wide as f/5.6. The middle changes as well, so halfway through the zoom range you’ll end up with a widest aperture of about f/4.5. An aperture range is common with less-expensive zoom lenses, but if you pay more you can get a standard aperture throughout the range.
That’s pretty much all you need to know about aperture. The important thing to remember is that a wide aperture, like f/1.8, lets in more light and provides a shallow depth of field (meaning less of the photo appears in focus). A narrow aperture, like f/22, provides deeper focus but lets in less light. What aperture you should use depends on the situation and the type of lens you’re using, so experiment to see what effects you get and you’ll have a better idea of how your aperture setting affects your photographs.