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Understanding the Exposure Triangle in Photography

Understanding the exposure triangle in photography

For a photographer, understanding the exposure triangle is essential to creating correctly exposed and visually stunning images.

The exposure triangle is a concept that refers to the relationship between the three main camera settings:

1. Aperture

2. Shutter Speed

3. ISO

These are the three main elements on a camera that you must balance together to affect the exposure, depth of field, and image quality in your photography.

They are the key tools at your disposal that help you add or take away the amount of light that hits the sensor, and dictate the depth of field (or blur) within an image.

Understanding how they can work in unison together will allow you to manipulate the visual appearance of a shot in any given situation.

The natural or artificial light existing within the environment also plays a key role, of course - but that's not a setting on your camera!

The Exposure Triangle

The photography exposure triangle

So, you should now recognise that to capture a photograph in the way they envision, a photographer needs to strike the perfect balance between these three settings.

In this article, I’ll discuss the photography exposure triangle in-depth and explore how you can use it to improve your photo-capturing skills.


The aperture is arguably the most complex of the three settings, so let's begin there.....

Aperture refers to the opening in the lens through which light enters the camera - it's the world of f-stops - a term you may be a tad familiar with already.

If you're not familiar, fear not - we're going to attack it right now.

Read slowly.. and absorb every sentence before continuing to the next...

Aperture is measured in f-stops.

A lower number indicates a larger aperture (often termed as shooting "wide open") and thus more light entering the camera, while a higher number indicates a smaller aperture and less light entering.

It all sounds a bit back-to-front, which is confusing for beginners, but you'll wrap your head around it eventually.

A low f-stop number widens the aperture blades to let more light in & reduce depth of field, a high f-stop number narrows the aperture blades to let less light in & increases the depth of field.

For ease of understanding, if I say "wide open" in this article, I'm referring to a low f-stop number.

Choosing the right aperture to use for any given shot is what helps the photographer create those creamy, blurry backgrounds that you often see in portraiture shots (using lower f-stop numbers to shoot wide open), or to ensure everything is in sharp focus from foreground to background in many landscape shots (higher f-stop numbers).

Portrait image shot with low f-stop (f/1.4) to isolate subject from background, landscape image shot with high f-number (f/11) to maintain more focus throughout.

The Range of F-Stops

The f-stop range available to you is determined by the lens you're using, not the camera - the camera just allows the photographer to select which specific f-stop they want to use (provided they're shooting in manual or aperture-priority mode).

The f-stop numbers you find on different lenses typically range from f/1.2 through to f/22, and though it's rare to find, some lenses do offer lower and higher f-stops than this.

In most cases, professional level zoom lenses tend to only go as low as f/2.8, while non-professional zoom lenses typically only offer as low as f/3.5 or f/4.

The very low apertures, such as f/1.2 or f/1.4, are usually reserved for prime lenses - these are lenses that have a fixed focal length, meaning they do not have any zoom.

The range of aperture blade openings on a lens as you go through the f-stops

Visual representation of the aperture blades on a lens narrowing as the f-stop number selected increases.

Most basic kit lenses that come with entry-level cameras have an f-stop range of around f/4 through to f/22.

Most lenses have a sweet spot where the sharpness of an image is at its best - a lens can often capture images that may appear slightly softer in certain areas when shooting at a very low or very high aperture, say f/4 and below or f/16 and above, though the capability and quality between lenses will differ.

With that said, unless you pixel-peep or plan to blow the image up to a gigantic size, it's very unlikely to ever be troublesome with the vast majority of lenses - it's just something I felt worth pointing out.

But what about zoom lenses that say f/3.5-5.6....?

Sometimes you'll see something like f/3.5-5.6 or f/4-5.6 - this means that you can choose an aperture as low as f/3.5 when shooting at a wide angle, but if you zoom in you'll reach a point where the lowest aperture you can use is f/5.6.

This typically applies to kit zoom lenses or beginner zoom lenses, not fully pro zoom lenses.

For example, if you have an 18-55mm zoom lens with an aperture range that can go as low as f/4-5.6, it means when shooting wide at 18mm you can select an aperture as low as f/4, but once you zoom in you'll reach a point where you are only able to shoot as low as f/5.6.

Aperture markings on a camera lens

When shooting wide open with a lower f-stop number it creates a shallower depth of field, which can be used to create a blurred background or to isolate the subject.

I'd personally deem a "low f-stop number" to be anywhere from f/1.2 to f/4.

Any f-stops higher than that and the isolation of the subject from the background tends to become significantly less.

Lenses that allow you to shoot wide open with a very low f-stop number, such as f/1.2 or f/2.8, tend to be professional grade, very heavy, and very expensive - though this isn't always the case, as some brands offer a super light and inexpensive 50mm f1.8 lens at a very affordable price (pssstt... Canon...) which is fantastic for beginners who want to get to grips with shooting wide open.

Shutter Speed

Now, moving on to the shutter speed...

Shutter speed refers to the amount of time the camera’s shutter remains open, allowing light to reach the camera sensor - so this is basically how long it takes for the camera to capture the image.

A young boy smartly dressed taking a photo

Do you know that click sound you can often hear when someone takes a photograph?

Sort of like a "ka-chick".

If someone fires off several photos, you can hear "ka-chick, ka-chick, ka-chick, ka-chick".

Well, that's the sound of the shutter, and it can close at different speeds depending on the shutter speed you set.

It is measured in fractions of a second, and a faster shutter speed allows less light into the camera as it is open for less time while the shot is taken, whereas a slower shutter speed allows more light to enter as it's open for longer.

A fast shutter speed can freeze motion, so it's great for capturing moving objects such as cars or people running.

As it lets less light in during the shot, a fast shutter speed is also useful for super sunny days when there is tons of bright light. A fast shutter speed can be literally a split millisecond.

A slower shutter speed is open for longer, so it's useful for capturing motion blur - such as running water - or for when the environment you're shooting in is dark and you want the shutter to stay open for longer during the shot to let more light in. A slow shutter speed can be a second or many seconds long, or even just half a second depending on the circumstances, but you'll have to use a tripod once you get to a certain speed.

Image shot with a fast shutter speed to freeze the motion of runners & an image shot with a slow shutter speed to capture the motion of a waterfall.

Try taking a photo handheld with a shutter speed of even just 1 second. This means it takes one full second to actually capture the image - so any slight minuscule mini-movement during that time can result in camera shake and the image being somewhat out of focus.

The 1/Focal Length Rule

If you're shooting handheld and wondering how slow of a shutter speed you can use and still get a shot that's in focus (assuming the subject you're shooting is relatively still), you could begin by adopting the basic 1/focal length rule.

For example, if you're shooting handheld with a 50mm lens, the rule says you should avoid using a shutter speed slower than 1/50. Likewise, if you're using a 70-200mm telephoto zoom lens and shooting at 125mm, you should avoid dropping your shutter speed below 1/125.

Of course, if the subject you're photographing is moving, then you may need to use a faster shutter speed than the 1/focal length rule indicates to capture the motion.

These days many professional grade lenses come with built-in image stabilisers to help assist with handheld camera shake at slower shutter speeds, plus some of us are generally a little shakier than others, but for capturing relatively still scenes and subjects, the 1/focal length rule is at least a good place to start.

Photographer Shawn Eastman capturing an image of a stunning landscape scene in Bali, Indonesia

In many situations, it's sadly not as straight forward as simply selecting the shutter speed and nailing the shot no matter what because the exposure still needs to be correct - this is why the exposure triangle involves all three settings working in harmony with each other as the photographer sees fit for the given situation.

For example, trying to capture motion blur of water flowing down a river during daylight can prove difficult as it's bright outside and leaving your shutter open for long enough to capture the motion can very easily overexpose the shot, leaving you with a bright white photograph.

To combat this, you'd have to look at using something like an ND filter, which darkens the environment as far as your lens and camera is concerned, allowing you to use a longer shutter speed in order to correctly expose the image and capture that motion blur.


And finally, ISO....

ISO measures the camera sensor’s sensitivity to light and allows a photographer to introduce more or less light as required by making the sensor more or less sensitive - it's sort of like a wild card mostly used for situations when you need a little more brightness in your image but don't have access to extra natural or artificial light.

A good example is wedding photography - a photographer in a dark church who isn't allowed to use flash or a tripod may find that shooting wide open with the lowest aperture available, and with a shutter speed that can't be any slower without introducing motion blur, still produces underexposed images due to the lack of light that's available - in this instance, increasing the ISO will introduce more light onto the sensor.

Increasing the ISO to introduce brightness to the shot does come with a trade off because it also introduces grain (technically referred to as "noise"), which decreases the quality of the image - although it has to be said that grain is often used in an arty way, or to give images a vintage look.

Plenty of people prefer grainy images in some cases!

First image shot with a low ISO resulting in minimal noise, second image shot with a high ISO resulting in a lot of noise.

Most modern cameras start with an ISO range of 100 (or sometimes as low as 50) to anything as high as 25,000+.

Each camera is different and capabilities are continually improving with newer models, so do check your particular model to find out its ISO range.

ISO 100 would have the least amount of noise, but also makes the sensor the least sensitive to light so a low ISO can only be used when the lighting situation within the scene you're shooting is adequate for what you want to achieve - such as natural outdoor daylight.

With that said, most modern cameras are capable of achieving perfectly acceptable quality when shooting as high as ISO 1600, sometimes even higher - you'll have to practice and see what you believe to be acceptable with your specific camera.

Remember, as the ISO number you select increases, so does its sensitivity to light, thereby making the image brighter (so handy for low-light situations), but this also introduces noise at the same time, thus reducing the quality of the image.

That's the Exposure Triangle in a Nutshell...

The exposure triangle is the relationship between these three elements.

By adjusting one or more of these elements, you can affect the exposure of the image, while keeping the unchanged elements constant.

For example, if you want to decrease the depth of field to make the background more blurry, you can decrease the aperture and increase the shutter speed, while keeping the ISO constant.

If you want to capture a little motion blur, you can decrease the shutter speed and increase the aperture, while keeping the ISO constant.

If you want to capture images in low-light conditions, you can increase the ISO and decrease both the aperture and shutter speed, while keeping the exposure constant.

It's all about capturing the image as well exposed as possible for the desired result you're after in most situations - I say most because some are just impossible without additional light!

Examples of the same image overexposed, underexposed, and correctly exposed.

With practice you'll be able to gauge a rough idea of the settings you need to use based on the type of image you want to capture and the environment you're shooting in - then you can make minor tweaks to perfect it through a little trial and error.

Understanding the exposure triangle and how to use it to your advantage is essential for any photographer.

It allows you to have more control over your images and helps you to create stunning photographs that are well-exposed and visually appealing.

The exposure triangle is a fundamental concept in photography that all photographers will greatly benefit from understanding - by mastering the relationship between aperture, shutter speed, and ISO, you can create visually stunning images that capture the moment and tell a story.

So the next time you’re out shooting, remember to adjust the exposure triangle to get the perfect shot.


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