The Key To Understanding The Exposure Triangle Lies With Goldilocks!

Share on facebook
Share on twitter
Share on reddit
Share on pinterest

Who doesn't love the exposure triangle, right?

Ahh the exposure triangle.

What’s so hard to understand about the exposure triangle?

It’s just three things, three tiny little things.

Well…. Sort of.

Once you get your head round it, it is actually pretty simple.

The triangle consists of three parts… duh!

1. The ISO

2. The Aperture

3. The Shutter Speed

It is a photographer’s job to carefully balance these three elements and to get them to work in harmony with each other, the result…. a well exposed image.

You alter one too much without adjusting the others and you’ll end up with a ruined image.

It will be your job as the photographer to master all three components and the best way to do this lies in understanding the exposure triangle at a deep level.

To fully manipulate the elements, you’ll have to make use of the different camera modes, particularly manual, program, aperture priority and shutter priority.

So here we go, the exposure triangle explained!


What does it stand for?

Well, it stands for International Organisation of Standardisation and they are the governing body responsible for standardising sensitivity ratings for camera sensors.

Before this standardisation came in you might have taken a photo at the equivalent of ISO 200 on one camera and taken the same shot with the same setting of ISO 200 on another and ended up with two completely different pictures.

What does it do?

The effects shown have been exaggerated using photo editing software for demonstration purposes.

Simply put, the ISO is a measure of how sensitive your camera sensor is to light.

A lower value means that the sensor is less sensitive to light and so it needs to be exposed to the light source for longer.

Conversely a higher value means that the sensor is more sensitive to light and doesn’t need to be exposed to the light source for as long.

This is something you can control with the other two elements of the exposure triangle.

As a rule the lower the ISO value, the better, more crisp the photo will be.

With a higher ISO comes noise, a grainy type effect that isn’t all that pleasing to look at. That said it can be used if that’s the look you’re going for and can be made to look quite nice under the right conditions.

The Aperture - f-stops

What is it?

The aperture refers to the size of the hole in the lens that lets the light in.

A wider aperture lets more light in and so doesn’t need to be exposed to the light source for as long. The wider the aperture, the lower the f number.

A narrower aperture lets light in and so needs to be exposed to the light source for longer. The narrower the aperture, the higher the f number. 

What's with the f numbers?

Written as f/2.8 or whatever value you set it to, the f number is actually referring to the dimensions of the opening in your lens.

And as it’s written as a fraction, for example f/1.8 or f/3.5, it should be seen and thought of as a fraction.

So an aperture of f/2 would be the equivalent of one half, f/4 one quarter and f/16 one sixteenth.

Which of these fractions is bigger?

Hopefully you said f/2 or one half! 

Meaning that an aperture of f/2 or one half would be bigger than f/4 or one quarter, making for a wider aperture.

You may understand it better through a little demonstration, so here’s the mathsy bit!

We’re trying to find out what the aperture of the lens is, so in other words, what is the diameter of the opening?

Lets say our f stop is f/2 for the sake of convenience.

The “f” stands for focal length.

And for this example we are using a 50mm lens, so our focal length is 50, you following?


So far we’ve got focal length/f value.

In our example this would be 50/2

All good!

Now to get the diameter you simply read it as a fraction so that would be 50 divided by 2 which will give us our diameter of 25mm.

So an f stop of f/2 with a 50mm focal length would give you an aperture of 25mm.

What does it do?

The main reason that we use aperture is to control the depth of field.

Depth of field refers to how much of your shot is in focus at specific depths.

A wide aperture, the lower f stops, will give you a shallow or small depth of field and would mean that there is only a small section at a certain depth that would be in focus, the rest would be out of focus and blurred.

A narrow aperture, the higher f stops would give you a deep or large depth of field and would mean that a large proportion if not all of the shot would be in focus irrespective of depth.

You often see a shallow depth of field, with wide apertures being used for portrait photography, the blurred background really helps the perfectly in focus subject to stand out.

On the other end of the scale you’ll see a large depth of field, with narrow apertures being utilised in almost all landscape photography photos as it allows for the whole shot to be in focus. 

The Shutter Speed

What is it?

Shutter speed is exactly what it say on the tin, it is the length of time that the shutter remains open and thus how long it exposes your sensor to light.

A longer shutter time means more light to the sensor and a shorter shutter speed means less light… simples!

The shutter speed is measured in seconds and is written as a fraction for example 1/4000s when below one second and after that is often written as the number of seconds with a double prime or quotation marks like this 3″ would be three seconds.

When to use different speeds?

You’ll need to use different shutter speeds depending on what it is you’re photographing and also the conditions in which you are shooting.

If you’re shooting a landscape then I doubt very much that the mountain will just get up and start sprinting so for shots like this you can use a slower shutter speed.

However if you like action shot or maybe sports photography then you will definitely want to be using a much quicker shutter speed to capture the action, if you were to use a slower shutter speed you’d just end up with a blur.

Having said that you can use a slower shutter speed for action shots intentionally if you are looking for that motion blur effect which when done right can be very effective. 

Or maybe you’re interested in long exposure photography, slowing your shutter speed right down can create some remarkable results, I’m sure you’ve seen those pictures of roads at night where you can only see the cars’ lights, that’s thanks to your good old buddy shutter speed.


If you rarely use a tripod and for the most part you are shooting without any kind of stabilisation then you may be forced to work with faster shutter speeds.

Slow shutter speeds and shaky hands do not a good photo make!

If you intend to take a lot of photos with a slower shutter speed, maybe you are into landscape or night photography then you should definitely get a good, stable tripod. You may find it quite a struggle without one.

To go with this a remote shutter release might come in handy to totally eliminate any kind of camera shake.

Using the Exposure Triangle

As a photographer it is your job to become the master of these three elements, manipulating them to suit your situation.

But how do you do it?

The best way to explain is to use a good analogy!

Goldilocks and her Bucket!

It might sound a bit stupid but sometimes the easiest way to understand something is through the use of a slightly dodgy analogy!

Everyone knows that Goldilocks is on the world’s most wanted list for breaking and entering, but did you know that she was also an expert photographer?

Goldilocks holds the secret to understanding the exposure triangle.

The goal is to fill her bucket with 1kg of porridge (the perfect exposure level) by manipulating the variables:

The porridge cloud / Aperture:

Very rare, but they do exist!

In this case when there is a heavy downpour of porridge, that is when the aperture is wide open, a low f number. In other words, loads of porridge rain equals lots of light.

When there is only a light drizzle, that is a narrow aperture, a high f number. In other words less porridge rain equals less light.

The time elapsed / Shutter Speed:

This is simply the amount of time that Goldilocks waits for her bucket to fill up or how long the shutter remains open.

The porridge bucket / ISO:

A narrow bucket (low ISO) will fill up slower, whereas a wide bucket will fill up much quicker (high ISO).

Scenario 1 - Fixed ISO

In this scenario, Goldilocks could either put the bucket (fixed ISO) out in the light porridge rain (less light / narrow aperture / high f-stop) for a long time (slow shutter speed).

Or she could put the bucket (fixed ISO) out in the porridge downpour (lots of light / wide aperture / low f-stop) for a much shorter amount of time (a fast shutter speed).

If she chose either of these options, she would end up with the perfect amount of porridge (exposure)…. Just right!

Had she of decided to switch the variables, she would have ended up with either too much or too little porridge (over or under exposed).

If she put the bucket (ISO) out in the porridge downpour (wide aperture / low f-stop) for a long time (slow shutter speed) she would end up with far too much porridge (an over exposed image).

And on the other hand if she put her bucket (ISO) out in the porridge drizzle (narrow aperture / high f-stop) for a short amount of time (fast shutter speed), she would end up with too little porridge (an under exposed image).

Scenario 2 - Fixed Aperture

This time with the consistent porridge rain (aperture), Goldilocks has two choices.

She can either use a shallower and wider bucket (a high ISO) that will capture more porridge quicker, so she’ll only need to leave her bucket out for a short amount of time (fast shutter speed).

Or, she can use a narrower bucket (a low ISO) that will take longer to fill, so she’ll need to leave it for a longer amount of time (slow shutter speed).

As with the previous scenario, if she was to change any of the other variables, she would end up with a poor result.

If she’d used the tall bucket (low ISO) and didn’t leave it for very long (fast shutter speed), the bucket wouldn’t fill up anywhere near as quick as the wider bucket and so she’d end up with an under filled bucket (underexposed image).

The same goes for if she’d used the wide, shallow bucket (high ISO) and left it out for too long (slow shutter speed), she’d end up over filling it (over exposed image).

Scenario 3 - Fixed Shutter Speed

So Goldilocks is short on time, she’s got another house to rob in ten so she needs to make it snappy!

Lucky for Goldilocks she has two choices, there is torrential porridge rain in the front garden (lots of light / wide aperture / low f-stop).

Or in her back garden there is only a porridge drizzle (less light / narrow aperture / high f-stop).

So she can either take her big, shallow, wide bucket (high ISO) and put it in the back garden where there is only a porridge drizzle (narrow aperture / high f-stop).

Or she can take her tall narrow bucket (low ISO) and put it in the front garden where there is a porridge downpour (wide aperture /  low f-stop).

Once again if she was to change the variables, she would end up with too much or too little porridge (over or under exposed image).

In other words if she took the wide bucket (high ISO / more sensitive to light) that is quicker to fill and put it in her front garden where there is heavy porridge rain (lots of light / wide aperture / low f-stop), she would end up with too much porridge (an over exposed image)

Or if she took her tall, narrow bucket (low ISO / less sensitive to light) and put it in the back garden where there is only a porridge drizzle (less light / narrow aperture / high f-stop), she would end up with far too little porridge (an underexposed image).

Goldilocks' lesson!

As I said, it sounds stupid but sometimes it takes stupid to help get your head around a complicated concept!

All about Stops

Stops are the increments in which the exposure triangle components either increase or decrease.

When you increase or decrease one of the exposure triangle’s settings by one stop, you are doubling or halving the amount of exposure.

Whether an increase in one stop equals double or half the amount of exposure depends on the setting you are adjusting.


The increments of stops for the aperture are as follows f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 and f/22.

F/1.4 allowing for the most exposure and f/22 allowing for the least.

When you increase the f-value by one stop (note I say one stop and not just 1), you decrease the amount of exposure by half.

So when you do this the aperture, the opening in the lens reduced by half.

Simply put:

Increase by 1 stop = Half the exposure eg. f/1.4 to f/2 

Decrease by 1 stop = Double the exposure eg. f/2 to f/1.4 

Shutter Speed

Try capturing action like this with a slow shutter speed and you'll end up with a blur.

Shutter speed stops are very simple to work out.

You simply double or halve the time to get your new stop, for example:

Let’s start with a shutter speed of 1/100s.

To work out your stop in either way you simply double it or halve it.

Slowing down the shutter speed by 1 stop would be 1/100s divided by 2 to get half which equals 1/50s, this would double the exposure time.

Speeding up the shutter speed by 1 stop would be 1/100s multiplied by 2 to get double which equals 1/200s, this would halve the exposure.

Simply put:

Speed up by 1 stop = Half the exposure eg. 1/100s to 1/200s 

Slow down by 1 stop = Double the exposure eg. 1/100s to 1/50s


In lower light conditions you may have to increase you ISO setting but beware of the dreaded noise!

ISO stops like shutter speed are very simple to work out.

To increase by one stop you double the value, giving you double the level of exposure.

To decrease by one stop you halve the value, giving you half the level of exposure.

Simply put:

Increase by 1 stop = Double the exposure eg. ISO100 to ISO200

Decrease by 1 stop = Half the exposure eg. ISO200 to ISO100

Using stops with the Exposure Triangle

Like with Goldilocks and her bucket, you can use the stops to make quick adjustments to balance all of your elements and get the perfect exposure.

So lets say that you’ve got the perfect camera settings for your shot but you want to try something a little different.

You’re taking a portrait shot, the exposure levels are perfect but this time you want more of a blurred background, so you widen the aperture by 1 stop, say from f/5.6 to f/4, in doing this you have doubled the exposure.

If you left it like this your picture would be over exposed and too bright.

To counter this you could either decrease the ISO value by 1 stop, halving the exposure or speed up the shutter speed by one stop, also halving the exposure.

This effectively cancels out the increased exposure that the wider aperture has given you resulting in your perfect exposure that you started with.


Now it’s time to practice.

Try things out, test them and experiment. This is the best way to learn about the exposure triangle.

As you improve, the exposure triangle will become more and more important to your success as a photographer and it will be something that you will have to constantly keep in mind to take the best photos you can.

I hope that this article has helped in understanding the exposure triangle and if you have any questions or are still unsure leave a comment below.

Like this article?

Share on facebook
Share on Facebook
Share on twitter
Share on Twitter
Share on reddit
Share on Reddit
Share on pinterest
Share on Pinterest

Related Posts

Leave a Comment

Your email address will not be published. Required fields are marked *