Understanding Aperture in Photography

Aperture is one of the three pillars of photography (the other two being Shutter Speed and ISO, which are two other chapters in our Photography Basics guide). Of the three, the aperture is certainly the most important. In this article, I go through everything you need to know about aperture and how it works.

What is Aperture?

Aperture can be defined as the opening in a lens through which light passes to enter the camera. It is an easy concept to understand if you just think about how your eyes work. As you move between bright and dark environments, the iris in your eyes either expands or shrinks, controlling the size of your pupil. In photography, the “pupil” of your lens is called aperture. You can shrink or enlarge the aperture size to allow more or less light to reach your camera sensor. Aperture can add dimension to your photos by controlling the depth of field. At one extreme, the aperture gives you a blurred background with a beautiful shallow focus effect. This is very popular for portrait photography. At the other extreme, it will give you sharp photos from the nearby foreground to the distant horizon. Landscape photographers use this effect a lot. On top of that, the aperture you choose also alters the exposure of your images by making them brighter or darker.

How Aperture Affects Exposure

Aperture has several effects on your photographs. Perhaps the most obvious is your images’ brightness or exposure. As the aperture changes in size, it alters the overall amount of light that reaches your camera sensor – and therefore the brightness of your image. A large aperture (a wide opening) will pass a lot of light, resulting in a brighter photograph. A small aperture does just the opposite, making a photo darker. In a dark environment – such as indoors or at night – you will probably want to select a large aperture to capture as much light as possible. This is the same reason why people’s pupils dilate when it starts to get dark; pupils are the aperture of our eyes.

How Aperture Affects Depth of Field

The other critical effect of the aperture is the depth of field. Depth of field is the amount of your photograph that appears sharp from front to back. Some images have a “thin” or “shallow” depth of field, where the background is completely out of focus. Other images have a “large” or “high” depth of field, where both the foreground and background are sharp. One trick to remember this relationship: a large aperture results in a large amount of both foreground and background blur. This is often desirable for portraits, or general photos of objects where you want to isolate the subject. Sometimes you can frame your subject with foreground objects, which will also look blurred relative to the subject.

What Are F-Stop and F-Number?

So far, I have only discussed aperture in general terms like large and small. However, it can also be expressed as a number known as “f-number” or “f-stop”, with the letter “f” appearing before the number, such as f/8. Most likely, you have noticed aperture written this way on your camera before. On your LCD screen or viewfinder, your aperture will usually look something like this: f/2, f/3.5, f/8, and so on. Some cameras omit the slash and write f-stops like this: f2, f3.5, f8, and so on. So, f-stops are a way of describing the size of the aperture for a particular photo. If you want to find out more about this subject, we have a comprehensive article on f-stop that explains why it’s written that way and is worth checking out.

Large vs Small Aperture

There’s a catch – one important part of the aperture that confuses beginning photographers more than anything else. This is something you need to pay attention to and get correct: Small numbers represent large apertures, and large numbers represent small apertures! That’s not a typo. For example, f/2.8 is larger than f/4 and much larger than f/11. Most people find this awkward since it goes against our basic intuition. Nevertheless, this is a fact of photography. This causes a huge amount of confusion among photographers because it’s completely the reverse of what you would expect at first. However, there is a reasonable and simple explanation that should make it much clearer to you: Aperture is a fraction. When you are dealing with an f-stop of f/16, for example, you can think of it like the fraction 1/16th. Hopefully, you already know that a fraction like 1/16 is much smaller than the fraction 1/4. So, if photographers recommend a large aperture for a particular type of photography, they’re telling you to use something like f/1.4, f/2, or f/2.8. And if they suggest a small aperture for one of your photos, they’re recommending that you use something like f/8, f/11, or f/16.

How to Pick the Right Aperture

Now that you’re familiar with large vs small apertures, how do you know what aperture to use for your photos? Let’s revisit two of the most important effects of aperture: exposure and depth of field. If you’ve read the prior chapter in our Photography Basics guide covering shutter speed, you already know that the aperture isn’t the only way to change how bright a photo is. Nevertheless, it plays an important role. In the graphic above, if I didn’t allow myself to change any other camera settings like shutter speed or ISO, the optimal aperture would be f/5.6. In a darker environment, where you aren’t capturing enough light, the optimal aperture would change. For example, you may want to use a large aperture like f/2.8 at night, just like how our eye’s pupils dilate to capture every last bit of light. As for depth of field, recall that a large aperture value like f/2.8 will result in a large amount of background blur (ideal for shallow focus portraits), while values like f/8, f/11, or f/16 will give you a lot more depth of field.

Setting Aperture in Your Camera

If you haven’t guessed it already, I highly recommend selecting your aperture manually as a photographer. If you allow the camera to set it automatically, you are likely to end up with the completely wrong depth of field in your image. There are two modes in photography which allow you to select the aperture manually. These are aperture-priority mode and manual mode. Aperture-priority mode is written as “A” or “Av” on most cameras, while manual mode is written as “M.” Usually, you can find these on the top dial of your camera. In aperture-priority mode, you select the desired aperture, and the camera automatically selects your shutter speed. You can select ISO manually or automatically. Aperture priority mode is great for everyday photography, where you rarely need to worry about any camera settings other than aperture. It’s what I use 95% of the time even for professional landscape and portrait photography.

Minimum and Maximum Aperture of Lenses

Every lens has a limit on how large or how small the aperture can get. If you take a look at the specifications of your lens, it should say what the maximum and minimum apertures are. For almost everyone, the maximum aperture will be more important, because it tells you how much light the lens can gather at its maximum (basically, how dark of an environment you can take photos – and how much of a shallow focus effect you can achieve). A lens that has a maximum aperture of f/1.4 or f/1.8 is considered to be a “fast” lens, because it can pass through more light than, for example, a lens with a “slow” maximum aperture of f/4.0. That’s why lenses with large apertures usually cost more. By comparison, the minimum aperture is not that important, because almost all modern lenses can provide at least f/16 at the minimum. You will rarely need anything smaller than that for day-to-day photography. The maximum aperture of a lens is so important that it’s included in the name of the lens itself. Sometimes, it will be written with a colon rather than a slash, but it means the same thing.

Everything Aperture Does to Your Photos

Ever wondered how else aperture affects your photographs aside from brightness and depth of field? In this part of the article, we will go through all other ways aperture impacts your images, from sharpness to sun stars, and tell you exactly why each matters. Diffraction is actually quite simple. When you use a tiny aperture like f/32, you literally squeeze the light that passes through your lens. It ends up interfering with itself, growing blurrier, and resulting in photos that are noticeably less sharp. At what aperture does diffraction start to become an issue? It depends upon several factors, including the size of your camera sensor and the size of your final print. Personally, on my full-frame camera, I see hints of diffraction at f/8, but it’s not enough to bother me. I actually use even smaller apertures like f/11 and f/16 all the time when I have a close foreground in landscape photography. However, I try to avoid f/22 or smaller, since I lose too much detail at that point. Diffraction isn’t necessarily a huge problem, but it exists. Don’t be afraid to take pictures at f/11 or f/16 just because you lose a little bit of sharpness. In many cases, the added depth of field is worth the tradeoff. In macro photography, diffraction can be a bit more of a problem close-focusing actually makes your effective aperture a lot smaller than it really is. Although the math behind that gets a bit complicated, basically, shooting at f/11 at macro distances will show diffraction a lot more compared to if you’re shooting a landscape at f/11. In other words, keep an eye out for diffraction when shooting macro.

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