What is Aperture in Photography? A UK Guide

This post may contain affiliate links. If you make a purchase through these links, we may earn a commission at no additional cost to you.

Ever taken a photo you thought would be brilliant, only to find it a bit… meh? Maybe you were trying to capture your dog’s goofy expression, but the garden fence behind him is annoyingly sharp. Or perhaps you wanted a grand, sweeping photo of the Cornish coast, but the whole thing looks a bit soft and blurry. Chances are, the culprit wasn’t your camera, but a little setting called aperture.

It sounds terribly technical, doesn’t it? Like something you’d need a degree in physics to understand. But honestly, it’s not. Aperture is one of the three superhero sidekicks of photography—along with its mates, Shutter Speed and ISO—and it’s arguably the most creative of the bunch. It’s the secret sauce behind those professional-looking portraits with dreamy, blurred backgrounds, and the magic ingredient for landscapes so sharp you feel you could step right into them.

Think of this guide as your friendly chat down the pub about photography. We’re going to unravel the mystery of aperture, piece by piece. We’ll ditch the baffling jargon and explain everything in a way that just makes sense. By the time you’ve finished reading, you’ll not only understand what aperture is, but you’ll be itching to grab your camera and use it to transform your photos from simple snaps into something you’d be proud to hang on your wall. So, grab a brew, get comfy, and let’s get started.

What on Earth is Aperture? The Simple Explanation

Before we get bogged down in numbers and settings, let’s start with a brilliantly simple idea. Think about the pupil in your eye.

When you walk out into the bright summer sun, your pupil gets tiny, shrinking to a little pinprick. It does this to limit the amount of light hitting the back of your eye so you aren’t blinded. Then, when you walk into a dark room or a dimly lit pub, your pupil opens up wide, becoming a big black circle. It’s trying to let in as much light as possible so you can see where you’re going.

In a nutshell, that’s exactly what aperture is.

Inside every camera lens, there’s a clever little mechanism called a diaphragm, which is basically a set of overlapping metal blades that form a hole in the centre. The aperture is simply the size of that opening.

A wide-open aperture (like your pupil in the dark) creates a large opening to let in lots of light.
A closed-down aperture (like your pupil in the sun) creates a small opening to let in very little light.

That’s it. That’s the core concept. It’s just a hole that can change size. This simple action does two incredibly important things: it controls the brightness of your photo and, more excitingly, it controls how much of your photo is in sharp focus. Let’s look at both.

Getting Technical: F-Stops and the Numbers Game

Okay, so we know aperture is a hole. But on your camera, you don’t see settings like “big hole” or “tiny hole.” Instead, you see numbers that look like this: f/1.8, f/4, f/11, f/22. These are called f-stops or f-numbers.

And here’s the first slightly odd thing you need to get your head around. It feels a bit backwards, but once you’ve got it, you’ve got it forever.

A small f-number (like f/1.8) means a large aperture opening.
A large f-number (like f/22) means a small aperture opening.

It’s confusing, right? Why would a smaller number mean a bigger hole? The ‘f’ stands for ‘focal length’, and the number is actually a fraction. Think of it like this: f/2 is like the fraction 1/2. And f/16 is like the fraction 1/16. We all know that 1/2 is much bigger than 1/16. So, f/2 is a much wider opening than f/16.

Here’s a simple way to remember it:

F-Stop Number	Aperture Size	Amount of Light	Great For…
f/1.4, f/1.8	Very Large	Lots of light	Portraits, low light, blurry backgrounds
f/4, f/5.6	Medium	Medium light	Everyday photos, small groups, street scenes
f/11, f/16	Small	Little light	Landscapes, architecture, sharp details
f/22	Very Small	Very little light	Extreme detail (but can make images softer)

Each full ‘stop’ you move up or down (e.g., from f/2.8 to f/4, or from f/11 to f/8) either halves or doubles the amount of light coming into the camera. You don’t need to memorise the exact numbers, but understanding this relationship is key to taking control of your camera.

The Exposure Triangle: Aperture’s Best Mates

Aperture doesn’t work alone. It’s part of a team of three known as the Exposure Triangle. Exposure is just the technical word for the total brightness of your photo. The three members of the team are:

Aperture (The Size of the Hole): Controls how much light gets in at once.
Shutter Speed (The Speed of the Blink): Controls how long the light is allowed in for.
ISO (The Sensitivity): Controls how sensitive the camera’s sensor is to the light it receives.

Imagine you’re filling a bucket with water from a rain butt. The ‘exposure’ is a full bucket of water. You can achieve this in a few ways:

You could use a wide hose (wide aperture) and fill the bucket very quickly (fast shutter speed).
You could use a narrow hose (small aperture), meaning you’d need to leave the tap on for longer (slow shutter speed).
If the water pressure is low (like a dark day), you might need to increase the pressure (higher ISO) to help fill the bucket faster.

All three settings are in a constant balancing act. If you change one, you usually have to adjust one of the others to keep the exposure the same. For example, if you make the aperture smaller (e.g., from f/4 to f/8) to get more of a scene in focus, you’ve just reduced the amount of light. To compensate and keep your photo from being too dark, you’ll need to either use a slower shutter speed or increase the ISO.

Don’t panic! Modern cameras are brilliant and can handle most of this for you, especially when you use a mode like Aperture Priority.

The Magic of Depth of Field (DoF): From Blurry Backgrounds to Pin-Sharp Views

Right, we’ve covered how aperture affects brightness. But now we get to the really fun bit: its effect on what photographers call Depth of Field (DoF).

Depth of Field is simply the amount of your photo that is in acceptably sharp focus. It’s the difference between a photo where only the subject’s eyes are sharp, and one where every blade of grass from your feet to the distant mountains is crystal clear.

And it’s all controlled by your aperture. The rule is just as wonderfully backwards as the f-numbers:

A large aperture (a small f-number, like f/1.8) gives you a shallow depth of field. This means only a very small slice of the scene will be in focus, and the background (and foreground) will be beautifully blurry.
A small aperture (a large f-number, like f/11) gives you a deep depth of field. This means much more of the scene will be in focus, from the front all the way to the back.

Shallow Depth of Field in Action

This is the secret behind professional-looking portraits. By using a wide aperture like f/1.8 or f/2.8, you can focus on your subject’s face and let everything behind them melt away into a soft, creamy blur. This makes your subject pop from the background and removes any distracting elements, like your messy living room or a crowded street.

When to use a shallow DoF:

Portraits: To isolate your subject and create a beautiful, artistic look.
Wildlife Photography: To make that robin in your garden stand out from the jumble of branches behind it.
Food Photography: To focus on one delicious part of a dish and blur the rest.
Creative Shots: To draw the viewer’s eye to a specific detail in a scene.

Deep Depth of Field in Action

This is your go-to for epic landscapes. When you’re standing on a hill in the Peak District and you want to capture the stone wall in front of you, the sheep in the middle distance, and the rolling hills far away, you need it all to be sharp. By using a small aperture like f/11 or f/16, you can achieve exactly that.

When to use a deep DoF:

Landscape Photography: To get everything from foreground to background in focus.
Architecture: To capture all the details of a magnificent cathedral or a sleek modern skyscraper.
Group Photos: To make sure everyone, from the people at the front to those at the back, is sharp.

Understanding and using Depth of Field is probably the single biggest step you can take towards more creative and intentional photography. It’s how you, the photographer, decide what’s important in your picture.

Aperture Priority Mode: Your Secret Weapon for Creative Control

At this point, you might be thinking, “This is great, but do I have to juggle aperture, shutter speed, and ISO all at once? That sounds like a faff.”

Well, you don’t. Say hello to your new best friend: Aperture Priority mode.

On most cameras, you’ll find it on the main mode dial, usually marked as ‘A’ or ‘Av’ (for Aperture Value).

When you switch to this mode, you are in charge of two things: the aperture and the ISO. You choose the aperture you want based on the depth of field you’re after (e.g., f/2.8 for a blurry background portrait, or f/11 for a sharp landscape). The camera’s clever brain then automatically selects the correct shutter speed to give you a perfectly balanced exposure.

It’s the perfect halfway house between full automatic mode and scary full manual mode. It lets you take creative control over the most important artistic element—depth of field—while the camera takes care of the technical heavy lifting. For many professional photographers, Aperture Priority is the mode their camera lives in 90% of the time.

How to use Aperture Priority:

Turn your camera’s mode dial to ‘A’ or ‘Av’.
Use one of the control dials (check your camera’s manual) to change the f-number.
Set your ISO. A good starting point is 100 or 200 for a bright day, and 400-800 for an overcast day or indoors. You can also set it to Auto ISO.
Point your camera, focus, and shoot! The camera will do the rest.

Choosing Your Weapon: How Lenses Affect Aperture

You might have noticed that not all lenses can achieve those super-wide apertures like f/1.8. The aperture range is a physical characteristic of the lens itself.

The lens that probably came with your camera—often called a kit lens—is a marvel of engineering, but it usually has a variable maximum aperture. It might say something like 18-55mm f/3.5-5.6 on the side. This means that when you’re zoomed out at 18mm, the widest aperture you can use is f/3.5. But when you zoom in to 55mm, the widest you can go is f/5.6. An aperture of f/5.6 won’t give you that super blurry background you might be dreaming of.

Lenses that can open up really wide (to f/2.8, f/1.8, or even f/1.2) are known as “fast” lenses. They’re called this because their large aperture lets in so much light, allowing you to use a faster shutter speed, which is brilliant for freezing action and shooting in dark conditions without a flash.

These lenses are often prime lenses, meaning they have a fixed focal length (they don’t zoom). A classic example is the “nifty fifty,” a 50mm f/1.8 lens. They are relatively cheap, incredibly sharp, and the perfect first step into the world of creative aperture control. More expensive zoom lenses often have a fixed maximum aperture (like a 70-200mm f/2.8), meaning you can use that wide f/2.8 aperture no matter how much you zoom in.

Creative Aperture in Action: A Practical Guide for British Scenes

Theory is all well and good, but let’s put it into practice. Here are some starting points for different situations you’re likely to find yourself in here in the UK.

1. The Classic Portrait (Outdoors)

You’re taking a photo of a friend in the park. You want them to be the star of the show, not the dog-walker in the background.

Goal: Shallow depth of field.
Mode: Aperture Priority (A/Av).
Aperture: Set it to the widest your lens can go (the smallest f-number, e.g., f/1.8, f/2.8, or f/4).
Tip: Get closer to your subject and make sure there’s some distance between them and the background. This will maximise the blur. Focus carefully on their eyes.

2. The Sweeping Landscape

You’re on holiday in the Lake District or walking the Seven Sisters cliffs. You want everything sharp, from the flowers at your feet to the clouds on the horizon.

Goal: Deep depth of field.
Mode: Aperture Priority (A/Av).
Aperture: Set it to f/11. This is often called the “sweet spot” for landscape lenses, giving great sharpness across the frame. You could use f/16, but sometimes image quality can soften a little.
Tip: Use a tripod! A small aperture means a slower shutter speed, especially on a classic grey British day. A tripod will keep your camera perfectly still and your photo pin-sharp.

3. Bustling Street Photography

You’re in the heart of London or Manchester, trying to capture the energy of the city. You might want to isolate a single interesting person, or you might want to capture the whole busy scene.

For isolating a person: Use a wider aperture like f/2.8 or f/4. This will help them stand out from the chaos.
For the whole scene: Use a smaller aperture like f/8. This keeps most of the street in focus, telling a bigger story.
Tip: Street photography is fast-moving. Aperture Priority lets you set your desired depth of field and then forget about it, allowing you to react quickly to moments as they happen.

4. The Gloomy Day or Cosy Pub Shot

Let’s face it, we get a lot of low light in Britain. Whether it’s an overcast sky or the warm glow of a pub, you need to let in as much light as possible.

Goal: Avoid a dark, blurry photo.
Mode: Aperture Priority (A/Av).
Aperture: Set it as wide as possible (e.g., f/1.8). This lets in the most light, allowing the camera to use a faster, safer shutter speed to avoid camera shake.
Tip: You’ll probably need to increase your ISO too. Don’t be afraid of this! Modern cameras handle high ISOs brilliantly. A slightly grainy photo is much better than a blurry one.

Beyond the Basics: Advanced Aperture Tricks

Once you’ve mastered depth of field, there are a few other cool effects you can create by controlling your aperture.

Bokeh

You’ll hear photographers talk about bokeh a lot. Bokeh is not the blur itself, but the quality of the blur. Is it smooth and creamy, or is it messy and distracting? Good bokeh is soft and pleasing. The shape of the blurred highlights in the background is determined by the number and shape of the aperture blades inside your lens. Lenses with more (and more rounded) blades tend to produce more circular, pleasing bokeh. You achieve it by using a very wide aperture.

Sunstars (or Starbursts)

Ever seen a photo where a streetlight or the sun has sharp, star-like rays coming off it? That’s a sunstar. You create this effect by doing the opposite of bokeh: you use a very small aperture, like f/16 or f/22. The tiny opening causes the light to bend around the edges of the aperture blades, creating the starburst effect. It’s a great trick for cityscapes at night or landscape shots with the sun in the frame.

Diffraction

This is a little warning. While it’s tempting to think that the smallest aperture (like f/22 or f/32) will always give you the sharpest possible landscape photo, it’s not quite true. At these tiny openings, a physical phenomenon called diffraction occurs, where the light waves start to interfere with each other as they squeeze through the hole. This can actually make the whole image a tiny bit softer. For most landscape work, f/11 to f/16 is the perfect balance of getting a deep depth of field without losing sharpness to diffraction.

A Brief History of the Hole: From Pinhole to AI

The idea of using a hole to form an image is ancient. The ‘camera obscura’—literally a ‘dark room’ with a tiny hole in one wall—was described by Chinese and Greek philosophers over two thousand years ago. But it wasn’t until the 1840s that the first camera lenses with a controllable mechanical aperture, called ‘Waterhouse stops’, were made. These were simple metal plates with different-sized holes cut into them that you would slot into the lens.

The big breakthrough was the iris diaphragm, patented in the 1880s. This is the system of overlapping blades we still use today, which allows for smooth and continuous adjustment of the aperture size. For over a century, this was a purely mechanical process. Now, the blades are controlled electronically by the camera’s brain, reacting in milliseconds and even being influenced by AI-powered scene recognition. But the basic, brilliant principle remains exactly the same as it was over 140 years ago.

Common Aperture Blunders (And How to Avoid Them)

As you start experimenting, you’ll inevitably make a few mistakes. Everyone does! Here are some of the most common ones.

The Group Photo Fail: You’re taking a photo of a group of friends. You use f/1.8 because you want a blurry background. The result? The person you focused on is sharp, but the people standing slightly behind them are blurry.
- The Fix: For groups, you need more depth of field. Choose a safer aperture like f/5.6 or f/8 to ensure everyone is in focus.
The Soft Landscape: You took a beautiful landscape photo, but it just doesn’t look as crisp as you’d like. You check the settings and see you shot it at f/4.
- The Fix: Remember the rule: for landscapes, you need a small aperture. Dial it down to f/11 and use a tripod for maximum sharpness.
The “Why Can’t I Get a Blurry Background?” Problem: You’ve got your kit lens, you’ve set it to its widest aperture (say, f/5.6 when zoomed in), but the background is still stubbornly in focus.
- The Fix: A kit lens has limitations. To get more blur, try zooming out (which lets you use a wider aperture like f/3.5), get closer to your subject, and make sure there’s lots of space between them and the background. Or, consider investing in a prime lens like a 50mm f/1.8 – it’s a game-changer.

Conclusion: Mastering Aperture and Finding Your Style

We’ve covered a lot of ground, from the pupils in our eyes to the physics of diffraction. But hopefully, you can now see that aperture isn’t some scary, unknowable concept. It’s a simple tool, but an incredibly powerful one.

It’s the tool that lets you decide what your photo is about. Is it about this one person’s expression? Use a wide aperture and blur the world away. Is it about the epic scale of this incredible place? Use a small aperture and make every detail sharp.

Aperture is the heart of photographic creativity. It’s the difference between merely documenting a scene and interpreting it. The best way to master it is to go out and use it. Put your camera in Aperture Priority mode and leave it there for a week. Take photos of everything. Try shooting the same subject at f/2.8, then at f/8, then at f/16. See what happens. Pay attention to the background. Notice the difference in the final image.

Soon, it will become second nature. You’ll look at a scene and you’ll just know what aperture you need. You’ll be in control. And that’s when photography gets really, really exciting.

The Guide to Aperture in Photography: From Blurry Backgrounds to Pin-Sharp Panoramas

What on Earth is Aperture? The Simple Explanation

Getting Technical: F-Stops and the Numbers Game

The Exposure Triangle: Aperture’s Best Mates