Introduction to Aperture in Photography

Many photographers struggle with some of the most basic and fundamental concepts of exposure in photography, getting frustrated with not being able to take good pictures. Unfortunately, some get stuck in automated modes, preferring to let their cameras decide everything for them. In order to help our readers explore the full potential of their camera gear, we will start by exploring one of the pillars of photography – aperture (the other two being ISO and Shutter Speed). Without a doubt, Aperture is the most important of the three, simply because it affects so many different variables of an image. It can add dimension to your photographs by blurring the background, and it also alters the exposure of your images by making them brighter or darker. In this article, we will cover everything you need to know about aperture, all in very simple language.

By adjusting your Aperture, you can change the depth of field in an image, as shown here.

What is Aperture?

Aperture is a hole within a lens, through which light travels into the camera body. 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 your aperture. You can shrink or enlarge the size of the aperture to allow more or less light to reach your camera sensor. The image below shows an aperture in a lens:

Aperture is like the “pupil” for your camera system, which can open and close to change the amount of light that passes through. Note the nine aperture blades in this lens, which form a diaphragm to block any light that tries to pass, except through the center.

The technical definition of aperture is: “The opening in a lens through which light passes to enter the camera.”

Effects of Aperture: Exposure

Aperture has several effects on your photographs. One of the most important is the brightness, or exposure, of your images. As 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. Take a look at the illustration below to see how aperture affects exposure:

In a dark environment – 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 your pupils dilate when it starts to get dark.

Effects of Aperture: Depth of Field

The other critical effect of aperture is something known as 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 “deep” depth of field, where both the foreground and background are sharp.

This photograph has a thin depth of field – a “shallow focus” effect.

In the image above, only the word “Cougar” is in focus due to my careful choice of aperture. Specifically, I used a large aperture here, which naturally results in a shallow focus effect. If I had chosen a much smaller aperture, the entire photo from front to back might have appeared sharp, without any clear out-of-focus background.

One trick to remember this relationship: a large aperture results in a large amount of background blur. This is often desirable for portraits, or general photos of objects where you want a blurry background. For example, one reason why the photo below works well because it has a blurry background (and pleasing bokeh):

Taken at a large aperture with a portrait lens.

On the other hand, a small aperture results in a small amount of background blur, which typically is ideal for things like landscape and architectural images. In the landscape photo below, I used a small aperture to ensure that both my foreground and background were as sharp as possible from front to back:

Taken at a small aperture to avoid background blur as much as possible.

And here is a quick comparison to show the two side by side – a large aperture and a small aperture:

If you’re wondering, I adjusted my shutter speed to equalize the brightness of these two images.

What Are F-Stop and F-Number?

So far, we have only discussed aperture in general terms like large and small. However, every aperture can also be expressed as a number known as an “f-number” or an “f-stop.” Whenever you see an aperture value, the letter “f” will appear before the number, like f/8.

Most likely, you have noticed this on your camera before. On your LCD screen or viewfinder, your aperture will 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. For example, the camera below is set to an aperture of f/8:

Aperture is labeled in f-numbers. In this case, I’m using an aperture of f/8.

So, f-stops are a way of describing the size of the aperture (how open or closed the aperture blades are) for a particular photo.

Size of Aperture: Large vs Small Aperture

There’s a catch – one important part of aperture that confuses beginning photographers more than anything else. This is something you really need to pay attention to and get correct: Small numbers are large apertures. And large numbers are 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 we are used to having larger numbers represent larger values. Nevertheless, this is a basic fact of photography. Take a look at this chart:

As you can see, an f-stop like f/16 represents a much smaller aperture opening than something like f/2.8.

This causes a huge amount of confusion among photographers, because it’s completely the reverse of what you would expect at first. However, as strange as it may sound, there is a reasonable and simple explanation that should make aperture much clearer to you: Aperture is a fraction.

When you are dealing with an f-stop of f/10, for example, you can think of it like the fraction 1/10th. Hopefully, you already know that 1/10th is clearly much smaller than a fraction like 1/2. For this exact reason, an aperture of f/10 is smaller than an aperture of f/2. Looking at the front of your camera lens, this is what you’d see:

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 some specific examples of f-stops, how do you know what aperture to use for your photos? Let’s jump back to exposure and depth of field – the two most important effects of aperture. First, here is a quick diagram to demonstrate the brightness differences at a range of common aperture values:

Or, if you’re in a darker environment, you may want to use large apertures like f/2.8 to capture a photo of the proper brightness (once again, like when your eye’s pupil dilates to capture every last bit of light):

As for depth of field, recall that a large aperture like f/2.8 will result in a large amount of background blur (ideal for shallow focus portraits), while apertures like f/8, f/11, or f/16 will help you capture sharp details in both the foreground and background  (ideal for many landscapes).

Don’t fret if your photo is too bright or dark at your chosen aperture setting. Most of the time, you’ll be able to adjust your shutter speed to compensate – or raise your ISO if you’ve hit your sharp shutter speed limit.

Here is a quick chart that lays out everything we’ve covered so far:

Setting Your Aperture

If you want to select your aperture manually for a photo (which is something we highly recommend), there are two modes which work: aperture-prioritymode and manual mode. Aperture-priority mode is written as “A” or “Av” on most cameras, while manual is written as “M.” Usually, you can find these on the top dial of your camera (read more also in our article on camera modes):

In aperture-priority mode, you select the aperture, and the camera automatically selects your shutter speed. In manual mode, you select both the aperture and shutter speed manually.

 Lens Limitations: Which Apertures Are Available?

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 capture at its maximum (basically, how dark of an environment you can take photos). A lens that has an aperture of f/1.4 or f/1.8 as the maximum aperture 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.

The minimum aperture is not that important, because almost all modern lenses can provide at least f/16 as the minimum aperture. You will rarely need anything smaller than that for day-to-day photography.

With some zoom lenses, the maximum aperture will change as you zoom in and out. For example, with the Nikon 18-55mm f/3.5-5.6 lens, the largest aperture shifts gradually from f/3.5 at the wide end to just f/5.6 at the longer focal lengths. More expensive zooms tend to maintain a constant maximum aperture throughout their zoom range, like the Nikon 24-70mm f/2.8. Prime lenses also tend to have larger maximum apertures than zoom lenses, which is one of their major benefits.

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 (like the Nikon 50mm 1:1.4G below).

Conclusion

Aperture is clearly a crucial setting in photography and it is possibly the single most important setting of all. That’s because depth of field and exposure have such major effects on an image, and your choice of aperture changes both of them. Aperture also has a number of other effects that are too extensive to fit in this article. So, we have another article that covers every single effect aperture has.

Knowing how important aperture is, it shouldn’t be a surprise that, at Photography Life, we shoot in aperture-priority or manual mode 100% of the time (with aperture-priority mode most of all). We never want the camera to select the aperture for us. It’s just too important, and it is one of those basic settings that every beginner or advanced photographer needs to know in order to take the best possible images.