Aperture is very similar to the “pupil” of your camera lens. Just like the pupil in your eye, it can open or shrink to change the amount of light that passes through. This is how the aperture blades look on a typical lens:
Your lens probably looks something like this. The shape in the middle is called the aperture. It is made up of several blades – nine of them in this case, but your lens may differ.
Aperture blades work a lot like the pupil in your eyes. At night, your pupils dilate so you can see things more easily. The same is true for aperture. When it is dark, you can open the aperture blades in your lens and let in more light. Aperture is written as f/Number. For example, you can have an aperture of f/2, or f/8, or f/16, and so on.
It is very important to remember that aperture is a fraction. This is the biggest mistake beginners make when they talk about aperture. If you get this wrong, it will be difficult to remember how aperture works or use it yourself to capture the right exposure in the field.
Which aperture is larger? f/2 or f/16?
Because aperture is a fraction, all you need to do is remember some elementary math. 1/2 is larger than 1/16, which means that f/2 is the larger aperture.
Typically, the largest aperture you can set will be something like f/1.4, f/1.8, f/2, f/2.8, f/3.5, f/4, or f/5.6. It changes from lens to lens. The smallest aperture on most lenses is something like f/16, f/22, or f/32. This diagram demonstrates the relative sizes of various aperture settings:
So, which aperture setting is best for photography and capturing the proper in-camera exposure? It depends upon the photo. Aperture influences many parts of an image, but it has two effects that are more important than anything else: exposure and depth of field.
Aperture and Exposure
The larger your aperture, the brighter your photo – the more light you capture. Again, your pupils work just like this, too; they open or close to let in different amounts of light. So, when you are trying to expose a photo properly, it is crucial to pay attention to your aperture setting.
A large aperture lets in more light. Apertures like f/1.4 and f/2 practically let you see in the dark. On the flip side, a small aperture like f/16 (with nearly closed aperture blades) lets in far less light. If you try to photograph Milky Way at f/16, your final image will be essentially black.
By changing your aperture and shutter speed settings, you can capture exactly the amount of light you want – resulting in a photo with the proper exposure. That is what makes aperture so powerful.
Aperture and Depth of Field
The other important effect of aperture is on depth of field.
Depth of field is the amount of your scene, from front to back, that appears sharp. In a landscape photo, your depth of field might be huge, stretching from the foreground to the horizon. In a portrait photo, your depth of field might be so thin that only your subject’s eyes are sharp.
Aperture changes your depth of field, which makes a big difference if you want to capture the best possible photographs. Changing the depth of field in an image will alter the way it looks completely.
To be specific, small apertures (like f/11 or f/16) give you a large depth of field. If you want everything from front to back to appear sharp, those are good settings to use. Large apertures (like f/1.4 or f/2.8) capture a much thinner depth of field, with a shallow focus effect. They are ideal if you are trying to isolate just a small part of your subject, making everything else blurred.
In practice, the effects are quite clear. As your aperture gets smaller and smaller, your exposure will grow darker and darker, and your depth of field will increase. (Remember, too, that you can expose the photo back to normal by using a longer shutter speed.) The more photos you take, the less you will have to think about these effects. They will become second nature.
The Aperture Scale
The shutter speed scale is easy to remember. An exposure of 1/100 second lets in twice as much light as an exposure of 1/200 second, because it is twice as long. Unfortunately, aperture is not as intuitive. This is the scale it follows instead:
From f/1.4 to f/2.0 (or any other one-stop jump) you will capture half as much light. You also will increase your depth of field. Also, keep in mind that you might be able to set values beyond this chart, like f/32, as well as apertures between these stops, like f/6.3, depending upon your lens.
Typically, the sharpest apertures will be somewhere in the middle of the range. On most lenses, f/4, f/5.6, and f/8 are three of the sharpest apertures. However, this varies from lens to lens. In addition, sharpness should not be your main concern. It is better to have a photo with the proper depth of field, even if it means that some low-level pixels have a bit less detail.