Aperture Explained: How to Control Depth of Field

TLDR: What Will You Learn

• Aperture is the adjustable opening in your lens that controls light and background blur.
• F-stops are the numbers you set, and a smaller number (like f/1.8) means a wider opening and more blur.
• Depth of field is how much of your shot is in focus, and aperture is your main lever to control it.
• Open wide for portraits and blurred backgrounds; close down for landscapes where you want everything sharp.
• Your lens, sensor size, and distance to your subject all affect how strong the blur looks.

What Aperture Actually Is

Let me start with the simplest way I know to explain this. Aperture explained in one line is the adjustable opening inside your lens that controls how much light reaches the sensor.

Think of it like the pupil of your own eye. When you walk into a dim room, your pupils widen to let in more light, and when you step out into harsh sunshine, they shrink to a pinhole.

Your lens does exactly the same thing, and once you understand this one control, I promise your photos start to look intentional rather than accidental.

The Iris and Blades Inside The Lens

Peer into the front of a camera lens and you will see a ring of overlapping metal blades. That is the iris, and together the blades form the opening we call the aperture.

When you set a wide aperture, the blades pull back to create a large hole. When you set a narrow aperture, they close in to leave only a small opening in the centre.

We measure this opening in f-stops, written like f/1.8 or f/16. The tricky part for beginners is that a small number (f/1.8) means a wide opening, and a large number (f/16) means a narrow one, so hold on to that, and it will click quickly.

How Aperture Affects Brightness

The size of that opening decides how much light floods onto your sensor, and that directly changes how bright or dark your image looks.

Picture yourself shooting a bowl of laksa at a dim hawker centre in the evening. The light is poor, so you open the aperture wide, say f/2.8, to gather as much of it as you can without a flash.

Now picture midday at Marina Bay, the sun bouncing off the water and the buildings. Here the scene is so bright that you narrow the aperture, perhaps to f/11, to stop the photo from blowing out into a washed-out white mess.

Same camera, same lens, two very different openings, all because the amount of available light changed.

How It Fits The Exposure Triangle

Aperture never works alone. It is one leg of what photographers call the exposure triangle, sitting alongside shutter speed and ISO.

Here is how I describe the three to my beginners:

• Aperture controls how much light comes in through the opening.
• Shutter speed controls how long the sensor is exposed to that light.
• ISO controls how sensitive the sensor is to the light it receives.

Change one, and you usually adjust another to keep the overall brightness balanced, like tuning a set of three sliders.

The good news is you do not need to master all three at once. Get comfortable with aperture first, because it is the control that shapes both your brightness and, as we will see, your depth of field, and the rest falls into place from there.

Making Sense of F-Stops

The single thing that trips up almost every beginner I teach is the f-number. It runs backwards from what your brain expects, and until it clicks, aperture feels like a cruel joke.

Let me sort that out for you here, because once you get it, everything else about aperture falls into place.

Why Smaller Numbers Mean Bigger Openings

Here is the counterintuitive bit. A small f-number like f/1.8 means a wide, open aperture that lets in loads of light. A large f-number like f/16 means a tiny opening that lets in very little.

Small number, big hole. Big number, small hole. Say that to yourself a few times.

The reason it works this way is that the f-number is actually a fraction of your lens focal length. That slash in f/1.8 is a real division sign.

So if your lens is 50mm and you set f/2, the aperture opening is 50 divided by 2, which is 25mm across. Set the same lens to f/16, and the opening is 50 divided by 16, which is barely 3mm.

Once you see it as a fraction, the maths stops being strange. A bigger denominator gives you a smaller result, which is why f/16 is a smaller hole than f/2.

The Full F-Stop Scale

Camera makers standardised a scale of aperture values so photographers everywhere speak the same language. The classic full stops run like this: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.

These numbers look random, but each one is roughly 1.4 times the one before it. That odd multiplier exists because the area of a circle scales with the square of its diameter, and 1.4 is close to the square root of 2.

You do not need to memorise the maths. You just need to know that stepping from one number to the next is a meaningful, consistent jump.

What One Stop of Light Means in Practice

Here is the payoff of that scale. Moving one full stop either halves or doubles the light hitting your sensor.

Go from f/8 to f/5.6, and you have doubled the light. Go from f/8 to f/11, and you have halved it. That is a full stop in each direction.

Picture a hobbyist at East Coast Park on a Sunday afternoon. She wants a soft portrait of her friend with the sea blurred behind, so she opens up to f/1.8 for a wide aperture and a shallow, dreamy background.

Later, the whole group gathers for a photo. Now she stops down to f/11 so everyone from the front row to the back stays sharp, accepting the smaller opening and adjusting her other settings to keep the exposure right.

Same lens, same park, two completely different looks. Understanding the f-stop scale is what lets you make that choice on purpose rather than by accident.

Understanding Depth of Field

Before we go deeper into settings, let me clear up one idea that trips up almost everyone I teach: depth of field.

Depth of field is the zone of your photo that appears acceptably sharp, stretching from just in front of your focus point to just behind it. Everything inside that zone looks crisp. Everything outside it softens into blur.

Think of it as a band of sharpness that hovers around whatever you focused on. Sometimes that band is razor thin. Sometimes it is wide enough to cover a whole street. Photographer Jeff Carlson sums it up simply: shallow depth of field is “having a plane that’s in focus, and everything else is out of focus.” This is where aperture explained properly starts to click. The size of that sharp band is controlled largely by how wide or narrow your aperture is.

Shallow Versus Deep Depth Of Field

A shallow depth of field means only a slim slice of the scene is sharp, with a soft, creamy blur in front of and behind your subject. A wide aperture, something like f/1.8 or f/2.8, produces this look.

A deep depth of field means far more of the scene stays in focus, from the foreground right through to the background. A narrow aperture, such as f/11 or f/16, gives you this.

Picture a visit to the National Orchid Garden at the Botanic Gardens. Open your aperture wide, focus on a single orchid, and that one bloom pops in sharp detail while the crowd and greenery behind it melt into gentle colour. That is shallow depth of field doing its job.

Now walk into a Chinatown street. Stop the aperture down to something narrow, and you can keep the shophouse facades, the lanterns overhead, and the hawker stalls all sharp at once. That is deep depth of field, and it works beautifully for scenes where the whole environment tells the story.

The Plane Of Focus

Here is a detail I want you to hold onto. Your camera focuses on a flat plane at a specific distance, not on your subject as a whole object.

The depth of field extends a certain distance in front of and behind that plane. So if you focus on the front petal of an orchid at a wide aperture, the back of the same flower may already be soft.

This matters most when you shoot close up or with wide apertures, because the sharp band gets very thin. Nailing focus on the exact spot that carries your message becomes the whole game.

How Depth Of Field Guides The Viewer's Eye

Depth of field is not just a technical setting. It is one of the most powerful storytelling tools you have.

When you blur a busy Chinatown background, you are telling the viewer where to look and what matters. Their eye goes straight to the sharp subject, because our eyes naturally rest on what is in focus.

Use it deliberately. Shallow depth of field to isolate and celebrate one thing, deep depth of field to show relationships and context. Every choice you make about that sharp band is really a choice about what story the photo tells.

Creating Beautiful Background Blur

That creamy, out-of-focus background you see in professional portraits has a name: bokeh. It refers to the aesthetic quality of the blurred areas in your photo, and getting it right is what separates a snapshot from something that looks intentional.

Now that we have covered aperture explained in the earlier sections, let me show you how to actually create that blur on purpose, not by accident.

The Three Factors Working Together

Here is the part most beginners miss. A wide aperture on its own does not guarantee dreamy blur. Three factors work together, and when you stack all three, the effect becomes dramatic.

The three levers are a wide aperture (a low f-number like f/1.8 or f/2.8), getting physically close to your subject, and increasing the distance between your subject and whatever is behind them.

Think of them like sliders. Push all three, and the background melts. Ignore two of them, and even an expensive lens will give you a busy, distracting shot.

A Tiong Bahru Cafe Example

Picture yourself photographing a flat white at one of the cafes along Tiong Bahru’s shophouse row. The wooden shelves and hanging plants behind the counter make a lovely backdrop, but only when they are soft.

Set your aperture wide open. Lean in close so the cup nearly fills your frame. Then make sure the shelves are a good few metres behind the cup rather than right up against it.

Do all three, and those shelves dissolve into soft washes of colour that flatter the cup without competing with it. That same recipe works beautifully for a portrait near the colourful Peranakan shophouses in Joo Chiat, where the pastel facades become a gentle blur of pink and green behind your subject’s face.

Bokeh Balls and Night Photography

Bokeh gets even more fun after dark. When you have out-of-focus point light sources in the background, they render as soft, glowing circles- the classic bokeh balls.

Shoot along Orchard Road during the Christmas light-up, place your subject a decent distance in front of the string lights, and open your aperture wide. Those distant bulbs turn into round orbs of light floating behind your subject.

A Recipe You Can Copy Today

Here is a simple sequence to try on your next outing:

1. Set your aperture to the widest your lens allows, such as f/1.8 or f/2.8.
2. Move close so your subject fills a large part of the frame.
3. Position your subject well in front of the background, ideally a few metres of separation.
4. Focus carefully on the eyes for a portrait, or the front rim of the cup for a flat lay.
5. Take the shot, then step back or forward slightly to fine-tune how much blur you get.

Master these three factors, and you can produce professional-looking bokeh with almost any subject in Singapore. Once your images look this polished, it is worth thinking about how you will use them. A solid content strategy helps that effort pay off for your brand.

When to Open Up Your Aperture

Now that we have covered the theory, let me show you exactly when to reach for a wide aperture (a low f-number like f/1.8 or f/2.8). Opening up your aperture is your go-to move whenever you want more light, a softer background, or a subject that pops off the frame.

Once you can recognise these three situations on sight, you will stop second-guessing your settings and start shooting with intent.

Portraits and Subject Separation

When I photograph people, I almost always open up. A wide aperture throws the background out of focus, so your subject stands cleanly apart from whatever is behind them.

Picture shooting a colleague for a LinkedIn headshot in an open-plan office. At f/8, you would see every messy desk and printer behind them, but at f/2.8 that clutter melts into a soft wash, and all the attention lands on their face.

That separation is what makes a portrait look intentional rather than like a random snapshot.

Low-Light Scenes

The second trigger is simple: not enough light. A wide aperture lets in more light, which lets you keep your shutter speed fast enough to avoid blur and your ISO low enough to avoid grain.

Here is a Singapore scenario I see all the time. A food blogger is shooting a beautifully plated dish at a dim, mood-lit restaurant along Keong Saik Road, and the tungsten glow is lovely for the diners but a nightmare for the camera.

Rather than crank the ISO and end up with a noisy, muddy shot, they open up to f/2.8. That extra light lets them expose the dish properly, and as a bonus, the neighbouring tables and hanging clutter behind the plate fall away into a creamy blur.

The plate becomes the hero, and the background stops competing for attention.

The Trade-Off You Must Respect

Here is the catch, and it is the one that trips up most beginners. A very wide aperture gives you a razor-thin depth of field, so only a sliver of your scene is truly sharp.

On a portrait shot wide open, this means you can nail focus on the tip of the nose and leave the eyes slightly soft, which instantly kills the image.

So make this your rule: when you shoot wide open on a person, focus on the eyes. Tap the eye on your phone screen, or move your camera’s focus point directly onto it.

The same logic applies to that plated dish. Focus on the front garnish or the section you want to draw the eye to, because at f/2.8 the back of the plate may already be drifting out of focus.

Open up for light and separation, but earn that shallow look by placing your focus deliberately every single time.

When to Close Down Your Aperture

We spent a lot of time on wide apertures and blurry backgrounds, so now let us flip the whole idea on its head.

Sometimes you want the exact opposite: everything sharp from the flowers in the foreground to the buildings on the horizon. That is when you close down your aperture, which means dialling in a higher f-number like f/8, f/11, or f/16.

Here is the counterintuitive part of aperture explained in plain terms: a bigger f-number is actually a smaller opening. The smaller the opening, the deeper your depth of field.

Landscapes and Cityscapes

Picture yourself at Marina Barrage at golden hour, trying to capture the whole skyline sweeping across the frame.

You want the grass in front of you, the water, and the towers in the distance all crisp. Shooting around f/11 gives you that front-to-back sharpness without pushing your lens too far.

The same logic applies to the Supertrees at Gardens by the Bay. If you want the pathway near your feet and the illuminated trees behind to both be in focus, a narrow aperture is your friend.

Narrow apertures also open the door to two fun effects. First, long exposures: by letting in less light, you can use slower shutter speeds to smooth out water or blur the light trails of traffic along the ECP.

Second, starbursts. Point your lens toward a streetlight along Orchard Road at f/16, and each light source blooms into a little sunstar. That crisp radiating effect only appears at narrow apertures.

Group and Architecture Shots

If you have ever taken a group photo and found the person in the back row soft while the front row is sharp, your aperture was too wide.

For a family shot of eight people at East Coast Park, close down to f/8 or f/11 so every face lands within the depth of field. The same goes for architecture: capturing the full facade of a shophouse in Tiong Bahru or the interior lines of a building demands edge-to-edge sharpness.

Getting the settings right for these scenes is a bit like planning a shoot list and workflow: you decide the outcome first, then choose the aperture that delivers it.

The Diffraction Limit

Now for the warning. You cannot just keep cranking the f-number to infinity and expect razor sharpness.

Past roughly f/16, an optical effect called diffraction starts to soften your entire image, even the parts that are technically in focus. The sweet spot for most lenses sits around f/8 to f/11.

Remember, too, that narrow apertures let in far less light. You will often need brighter conditions, a slower shutter, or a tripod to keep things steady, especially for those long exposures at Marina Barrage after sunset.

How Your Lens Changes the Result

Here is something that trips up a lot of beginners: you set your camera to f/2.8, your friend sets theirs to f/2.8, and yet your backgrounds look completely different.

That is because aperture, explained on paper, is only half the story. The same f-stop behaves differently depending on the lens you screw on and the camera behind it.

Prime Versus Zoom Lenses

Most people start with the kit lens that came bundled with their camera. These zoom lenses usually have a variable maximum aperture, often something like f/3.5 to f/5.6, meaning the widest you can open up shrinks as you zoom in.

That limits how much background blur you can achieve, which is why so many hobbyists feel their photos look flat compared to what they see online.

Prime lenses tell a different story. A prime has a fixed focal length and no zoom, but in exchange it often opens up to f/1.8, f/1.4, or even wider.

These are the lenses people call “fast primes”, and they are prized precisely because that wide aperture produces creamy, obvious background blur. A common first upgrade for photographers here in Singapore is a nifty fifty (a 50mm f/1.8), which is affordable and immediately transforms portrait shots.

Focal Length and Compression

Focal length matters too, and it works alongside aperture. Longer lenses (say an 85mm or 135mm) do two things: they magnify your subject, and they compress the background, making distant elements appear closer and larger.

That compression, combined with a wide aperture, melts the background into smooth blur far more dramatically than a wide-angle lens at the same f-stop.

Picture shooting a portrait at Gardens by the Bay. Stand back with an 85mm lens at f/2 and the Supertrees behind your subject dissolve into soft colour. Shoot the same scene with a 24mm wide-angle at f/2, and those trees stay recognisable.

Sensor Size and Smartphone Limitations

The biggest hidden factor is sensor size, and this is where many Singapore hobbyists get caught out. A larger sensor produces a shallower depth of field for the same framing, so a full-frame camera blurs backgrounds more easily than a crop-sensor body, which in turn blurs more than a smartphone.

Your phone’s sensor is tiny. That is why, even at a wide aperture, everything from your subject to the buildings behind them tends to stay in focus.

This is the crucial point: smartphones cannot create strong optical blur, so they fake it in software. When you use Portrait mode on an iPhone, the phone detects your subject, then artificially blurs everything else.

It looks convincing most of the time, but you have probably seen it slip up, blurring the edge of someone’s hair or a coffee cup they are holding.

If your camera is your phone, do not feel limited. Understanding how the software simulates depth of field and learning to work with good light and clean backgrounds will take you further than chasing blur you cannot optically produce.

Practice Exercises to Master Aperture

Reading about aperture only gets you so far. The intuition comes from shooting, and the good news is you can build it in a single weekend without leaving Singapore.

For all three drills, I want you to switch your camera or phone to Aperture Priority mode (marked A or Av on most cameras). This lets you pick the f-stop while the camera sorts out shutter speed and ISO, so you can focus purely on how aperture changes the look.

The Depth-Of-Field Comparison Drill

Pick one still subject, say a cup of kopi on a table at your neighbourhood hawker centre, and place a busy background a few metres behind it.

Shoot the same frame three times: once at f/1.8, once at f/5.6, and once at f/16. Keep your position and framing identical each time.

When you compare them side by side, you will see the background melt into a smooth blur at f/1.8, tighten up at f/5.6, and come into sharp focus at f/16. That single comparison teaches you more about depth of field than any diagram.

The Background-Distance Drill

Head to the Singapore Botanic Gardens and bring a friend as your model. This drill isolates one variable that trips up a lot of beginners: the distance between subject and background.

Set your aperture to something wide like f/2.8 and keep it there. Then photograph your friend standing right in front of a hedge, then a few steps away, then far away with the greenery well behind them.

Here is the takeaway: the further your subject stands from the background, the creamier that blur becomes, even at the same aperture. Try this quick sequence:

1. Subject one step from the foliage.
2. Subject three metres from the foliage.
3. Subject ten metres from the foliage, with open lawn behind.

You will notice the last shot has the dreamiest background, and you never touched your f-stop.

The Night Bokeh Drill

Come back after dark and walk along the Singapore River, where the boat quays glow with string lights and shop signs reflecting off the water.

Open your aperture as wide as it goes, focus on something close like a railing or a friend, and let the distant lights fall out of focus. Those out-of-focus lights render as soft glowing circles, the classic bokeh effect that makes night shots feel cinematic.

Experiment with focusing distance and watch how the size of those light circles changes.

If you enjoy learning this way and want structured guidance, a hands-on course can accelerate things, and your SkillsFuture Credit can subsidise many photography courses in Singapore. I am a fan of Equinet Academy’s practical hands-on training approach because that is exactly how aperture sticks: by doing, not just reading.

Conclusion

Remember that shot at Gardens by the Bay we started with, the one where the Supertrees stood proud but the whole frame felt flat and lifeless? You now have the tool to fix it.

Aperture is the creative lever that turns a snapshot into an image you meant to make. When you widen to f/2.8 to melt the background behind a friend, or stop down to f/11 to keep the entire Cloud Forest sharp, you are no longer letting the camera decide. You are telling the story.

The core loop is simple enough to carry in your head. Choose your f-stop for the depth of field your story needs, factor in your lens and sensor, then check your exposure and adjust.

The catch is that theory alone will not save you when the light is changing and the moment is passing. That only comes from repetition until the decision becomes instinct.

So put this into your hands. Walk around Marina Bay or your own neighbourhood and shoot the same subject at f/2, f/5.6, and f/16, then compare what changed. Do that a few weekends in a row and you will stop thinking about numbers and start seeing depth of field before you even raise the camera.

If you want structured, hands-on guidance to build this muscle memory faster, especially if you shoot mostly on the phone in your pocket, consider joining the Mobile Smartphone (iPhone & Android) Videography for Business and Marketing Course and Mobile Phone (iPhone & Android) Photography for Business and Marketing Course at Equinet Academy.

By joining you can now turn theory into confident, intentional shooting with practical coaching rather than another weekend of guesswork.