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Exposure Triangle for beginners: How ISO, Shutter Speed and Aperture work together and form Exposure Triangle

Shubham Davey 0
Reading Time: 12 minutes

Photography is cool unless you deal with exposure triangle. For many beginners, exposure triangle is a nightmare as it involves controlling all three giants of photography. ISO, Shutter Speed & Aperture are the pillars of digital photography and since these pillars are under your control, it becomes difficult to understand how to balance the exposure triangle.

A book by Bryan Peterson, Understanding Exposure is a must have book to understand Exposure Triangle.

What is Exposure Triangle made up of?

triangleAs the name suggests, there are three sides of this association each side being the pillar of digital photography. The ultimate aim is to balance these sides to perfectly expose your image sensor & the lens so that the resulting image is neither over-exposed nor under-exposed. Having said that, let me explain a lot of things that will help you master exposure triangle. So let’s begin

Side 1: Aperture

Aperture, according to me is the most important element in a DSLR. I call it the eye of the DSLR. The aperture controls the amount of light entering the lens and hitting the image sensor. Wider the aperture more light enters the lens and hence more objects come into focus in the scene.

aperture scale

The most important effect the aperture has on an image is focusing on objects you want to have in the frame. Furthermore, the aperture you work on affects the depth of field of the image. The depth of field is basically the are of the image in focus. Shallow DoF has less area in focus and deep DoF larger area in focus. One confusing part of the aperture is the f numbers/fstops. Depending on the lens you use, the fstop ranges from f1.4 to f22.

  • Large Depth of Field is a large portion of the image in focus(large f-stop number)
  • Small Depth of Field is a small portion of the image in focus(small f-stop number)

To make it simpler,

Remember it like this, smaller the f-stop, smaller the portion of the image will be in focus.

Side 2: Shutter Speed

Shutter speed is the measure of time (in seconds) for which the shutter of the lens is open. In other words, the shutter speed determines the intensity of the light hitting the sensor. Lower the intensity, lower is the light in the final image. Apart from this, Shutter Speed is to freeze the fast-moving subjects. Be it flowing water, moving animals, vehicles or any object. This is the major use of using this camera mode

Slower shutter speed (longer time) allows more light to enter the lens hence it can take great shots in lower light conditions. To capture a beautiful starry night, shutter priority mode has the major contribution along with a pinch of ISO and aperture.


Side 3: ISO settings 

ISO settings deal with the sensitivity of the light on the image sensor. ISO, just like the other two pillars work on light. The main reason why ISO is one of the three pillars is that it works in low light condition but it avoids noise to a very large extent. There is no separate mode for ISO, you can set ISO in any of the manual modes


ISO is measured in numbers starting from 100 to 6400. Some high-end DSLR also supports ISO beyond 6400. Higher ISO means lower sensitivity to the light. So if you are shooting in bright natural daylight, you will want to have ISO at least 400-800 and aperture wide open to balance the exposure triangle. In this case, shutter speed does not play any major role to compose the image. The main purpose of using ISO is to eliminate digital noise in low light conditions.

The basic idea behind these three settings is dealing with light. Each of these settings deals differently with light and effects the photos differently. Point is to balance these three to get a perfect photo you’d stare long.

This leads us to the next question.

How does Exposure Triangle work? 

exposure triangle
Source: FStoppers

Exposure triangle is like a game, mathematically speaking, your goal is to keep the triangle isosceles throughout your shoot. The isosceles triangle means the side remains the same. Now, to understand how to balance the exposure triangle, you need to understand the concept of stops of light. In photography, a stop is halving or doubling the amount of light composing the scene. To rightly lit a photo, you need a certain amount of light. The intensity of this light is determined by the stops of light. Each combination of these stops from the three sides of exposure triangle is known as Exposure Value(Ev)

Simply put, a stop is every time you go up or down in any of the three sides of the exposure triangle.

How ISO, Exposure, & Shutter Speed affect the Exposure Triangle

Now, you know that there are three things you need to control. Furthermore, considering stops in the individual of the three settings, you get thousands of stops to manage. But, let’s not complicate it here and keep it simple.

For any exposure, if you change any of the three value even by one stop, you should change the other two values by a similar number of stops. Consider this example, you are shooting a sprinting river stream at late evening. The light is minimum and you hate using flash (It kills the scene brutally)

So what do you do? Depending on the speed of the stream and light around, you will have to adjust the shutter speed. Again, shutter speed will give a silky effect on the water. But how you’ll make the silky effect visible? First, you will have to go one or two stops (maybe even higher) up in shutter speed (for the silky smooth effect) You have to go one or two stops down in ISO & same with aperture also. That’s how you balance the exposure triangle.

The basic idea is, if you down by one stop in any of the three variable, you will need to go up by one stop in the other two.

Best settings for Exposure Triangle

Ideally, there is no one answer. As I have mentioned earlier, there are a lot of combination of exposure values(EVs) that is one of the best settings for exposure triangle. However, depending on the scene you are shooting, you will be composing the Ev considering a lot of factors.

But where to begin?

Ideally, ISO 100 is default in so you can begin with having ISO 100. If you are shooting in low light, then you can have a bigger ISO number (to reduce the noise) slower shutter speed (one stop less than ISO) & aperture as needed. Considering the DoF, you can decide the aperture but the shutter speed and ISO should be inter-dependent.

Another example of bright daylight. Say you are shooting a bird in your backyard. Since the light is good, you won’t need higher ISO (unless you choose a very fast shutter speed and a high aperture)

Now, chances of the bird being immobile is very high, hence you will need a faster shutter speed to capture the bird’s movements. Such photos are more beautiful when shot as a macro shot, hence a narrow aperture (down stops) is needed to do this. So, to balance this you will have to go one stop up in ISO, may ISO 400 would do.

Practical explanation of exposure triangle

exposure triangle
Shutter Speed: 1/30 Aperture: f/22 ISO: 400 Flash: Not Fired  © Shubham Davey

This is the shot I took for this post, luckily got a great subject. The bird was in constant motion, hence I had to go with a fast shutter speed and narrow aperture (I’m a big fan of shallow DoF). First I shot at ISO 100, ISO 200 and the result was a shaky & over-exposed image. So I went one more stop up, at ISO 400 and the result is amazingly lit photo of nature’s beauty.

A catch here is, faster shutter speed than this would let lesser light and imbalance the exposure triangle. Faster Shutter speed ( around 1/60 or higher) at aperture f22 will let a very less amount of light inside the lens. However, there was an option of having ISO 800 & beyond to balance, but I chose the initial option over the latter. Reason? At high ISO, there are chances of saturated image and grains.

Exposure Triangle is something that comes with practice, each time you take a shot, note the readings & analyze how you can make it better. No doubt, you and I will fail a couple of times, but we have nothing to lose at this stage, right? You should definitely avoid imbalanced exposure triangle to keep the scene perfectly lit and exposed. Which takes us to the next question.

What is imbalanced exposure triangle & how to fix it?

Let’s assume you’re shooting in M mode, ISO is high, shutter speed is slower and aperture is wide open. You are shooting a birthday party, where kids are running around with a beautiful selfless smiles. You don’t wanna miss these scenes uncaptured. Furthermore, you are adamant to shoot in M mode, as the auto mode is too mainstream. Now what?

In other words, you have an imbalanced exposure triangle to deal with. Here’s what you can do to fix it real quick.

  • High ISO indoors will saturate images & bring grains due to artificial bright light. So higher ISO is not an option. Max ISO 400 is what you can afford in this case. At higher ISO, the light sensitivity will increase and you will have to have a faster shutter speed which may result in an under-exposed image.
  • Faster shutter speed is magic wand here. The tiny tots are running around and making a mess inside the house. Faster shutter speed (1/100 & beyond) will do great. Furthermore, a combination of ISO one stop down to Shutter speed is always fruitful. That is, if you go three stops up in shutter speed, go two stops up in ISO, in other words, keep the ISO one stop behind the shutter speed.
  • Aperture is like stem cells in human body, it works anywhere and adapts the situation perfectly. Hence, in this case, wider or narrow aperture would depend on the subject. However, aperture does affect the final image as it directly deals with the amount of light entering the lens.
    If you opt for a wider aperture that lets more light in (which you don’t need indoors) you will need a faster shutter speed (1/250 or higher) and one stop up in ISO. This will, imbalance the triangle as higher ISO will saturate the final image. So a narrow aperture (small f-number) will be the best indoor. Furthermore, the narrow aperture will result in shallow DoF resulting in stunning images you’d love to own.
    Alternatively, should you shoot with the aperture wide open, chose lowest ISO possible. This will not only remove grains, but it will also eliminate chances of saturation.

Pro Tip: Do consider the White Balance in such situations. Best white balance in such situation is “Incadecent” and if you are not familiar with it, leave it to auto WB to take care.

Final thoughts on Exposure Triangle

Take your time to learn about this in detail. You will have to experiment a lot as this involves the three pillars of photography. Initially, you can leave the ISO to the default value of ISO 100 and experiment with shutter speed. Aperture is optional, to begin with. But for a better quality of photos, get your hand dirty with changing the aperture too.

Apart from being the most important feature in digital photography, the aperture is the easiest one to learn and master. If you understand the basic concept of aperture, it is very easy to grasp. Shutter speed & ISO go hand in hand. Until you are the in safe zone of lowest ISO, mostly any shutter speed would do great. But if you chose to play with ISO, keep one thing in mind – every time you change the shutter speed (up or down) change the ISO without fail (up or down)

Both affect each other directly at higher levels of their stops. Always keep the ISO one stop behind the shutter speed. The amount of light entering the lens and the sensitivity of that light on image sensor will stay balanced. That’s how it works. That’s how it should be used. If you balance these two well, the aperture will be a piece of cake for you. I keep aperture two stops behind the shutter speed. Again, if my need is shallow DoF, I let go of this rule and expose accordingly.

All in all, the exposure triangle is must know technique to never let imbalanced Ev to ruin the final image. 

Over to you. How do you manage to balance exposure triangle? What’s the toughest Ev combination you have you have worked on? Let me know in the comment section below.

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