The Truth About the Exposure Triangle, and Should You Use It?

The Truth About the Exposure Triangle, and Should You Use It?

Making the relation between aperture, shutter speed, and ISO visible is the idea behind the exposure triangle. I have seen many beautiful drawings of the exposure triangle, but what does this diagram really show? Let’s find out.

When writing my Dutch e-book "Licht Vangen," which translates into Catching Light, I needed to cover the exposure triangle. Although I’m photographing for over four decades, I never used this diagram. But I have seen the many different versions on the internet, and inside popular photography magazines. These drawings often look amazing, covering more than exposure alone. Just do a search on Google, and see for yourself.

A search on Google will show a lot of different versions of the exposure triangle

Many photography courses cover the exposure triangle, emphasizing its importance in understanding the relation between aperture, shutter speed, and ISO. I even hear about photographers who claim to use the exposure triangle exclusively, to keep a perfect control over the exposure for every photo they take.

The Exposure Triangle in Detail

First, let’s have a closer look at the exposure triangle. If you know what is, you might want to skip this chapter. But perhaps it’s good to keep on reading, to have everything clear.

To understand the exposure triangle you must know about the settings we can use to get the exposure correct. Aperture is the first one, controlling the amount of light that goes through the lens. Shutter speed is the second one, controlling the time light is hitting the sensor. The ISO is the third one, and although it doesn’t control the amount of light in any way, it resembles the sensitivity of the analog film. I don’t want to go into depth about ISO, and keep it simple by assuming it is sensitivity.

Something similar to this exposure triangle can be found easily. But it doesn't tell anything about exposure.

These three setting need to be in balance in order to have the right exposure. By placing the three settings into a triangle, we can visualize the relation. Sometimes we see the aperture, shutter speed, and ISO at the corners, as if these settings are puzzle pieces that need to fit. More often we see these on the sides of the triangle, together with the possible values of each one. By drawing a line between each setting we can visualize a correct exposure in the triangle.

The exposure triangle with more information. By choosing the right values the correct exposure can be obtained. But can you tell which values to choose by looking at this drawing?

What the Exposure Triangle Doesn’t Show

By this simple description you might already see what wrong with this picture. You can draw random lines and end up with a every possible combination. It clearly doesn’t tell anything about a correct exposure.

Any line can be drawn inside the exposure triangle. But it doesn't guarantee a correct exposure.

To draw the correct lines inside the exposure triangle, you need to have a light meter that can measure the amount of light available. For that you need choose two settings, of course, and the light meter will measure the third one. Often we see how the ISO is kept as low as possible, and the aperture is used for a desired depth of field. In other words, you have the sensitivity of the sensor set, together with the amount of light that passes through the lens. With these two settings, you will need a light meter to know how much time is needed before the exact amount of light has hit the sensor.

Choose two settings, and let the third one be measured by the light meter inside the camera.

Let’s go back to those photographers that use the exposure triangle exclusively to keep control over the exposure. By using the exposure triangle alone, they won’t know the exact settings. They must use a light meter also.

What the Exposure Triangle Does Show

You need to choose two out of three settings, and measure the amount of light to know the third setting. Only then you can have a correct exposure. Since every modern camera has a light meter built in, you can set the ISO, and the aperture, just like in my example, and measure the corresponding shutter speed. For that you don’t need a exposure triangle.

But what if you end up with a shutter speed that is not to your liking. Perhaps it is too slow, but making it faster will lead to an under exposed image. After all, in that case the shutter isn’t open long enough to gather enough light for the correct exposure. In that case you need to change the aperture or the ISO to compensate the faster shutter speed. For that you can use the exposure triangle.

If you have determined a correct exposure, and you want to change on of the three settings, the exposure triangle can help you make the right correction. That is why a good exposure triangle mentions if you get with more light, or less light when changing a setting. This way you can read easily see in which direction you need to change a setting.

With the same shutter speed, it is possible to have different ISO and aperture combinations.

With the same ISO, it is possible to have different aperture and shutter speed combinations.
With the same aperture, it is possible to have different ISO and shutter speed combinations.

What More Can the Exposure Triangle Show?

Using an exposure triangle as mentioned in the previous chapter will help you understand the consequence of the compensation you might perform. Changing the aperture, shutter speed, and ISO does not only change the amount of light for the exposure. It also has an effect on the image.

Do you need help when to compensate a change of settings? This exposure triangle shows the effect regarding exposure.

As you know, the aperture is used to control the depth of field. A smaller aperture will increase the depth of field, while a larger aperture will decrease the depth of field. Shutter speed affects the motion of a subject. If shutter speed becomes longer, motion will become visible. And increasing the ISO, which is basically the signal amplification of the sensor, will lead to a higher noise level.

If you need a reminder how the aperture, shutter speed, and ISO affects the image, the information in this exposure triangle is of great value.

Most popular exposure triangles show these effects in some way or another. This way you will know what effect the exposure compensation will have on the image. If you compensate a faster shutter speed with the larger aperture, it will lead into a smaller depth of field. On the other hand, if you use the ISO to compensate it might lead into a higher noise level.

In this case, the exposure triangle isn’t showing the exposure, but the effect of depth of field, motion, and noise when changing settings. Be aware, the exposure triangle won’t show you the exact depth of field, motion blur, or noise levels. It is just telling you if the change will increase, or decrease these effects. The exposure triangle tells the relative effects, not the absolute ones.

Is It Wise to Use the Exposure Triangle?

The answer to this question can only be answered by you. I think it is possible to use the exposure triangle in a good way, but not for determining the exposure itself. If you have determined a correct exposure, the triangle can be used to see how you must compensate a change in setting, and what the effect on depth of field, motion blur, or noise levels will be on the end result.

Are you going to use an exposure triangle, make sure you use one that has all the information as visible in this example. It has all the information you need.

For me, the exposure triangle has no use. During my four decades of photography I have gained enough knowledge to know how to compensate a exposure setting, and how it will affect the image. But for the beginning photographer, or the one that has difficulties imagining these things, the exposure triangle can be very helpful. Just make sure you use one that mentions the effects of aperture, shutter speed, and ISO settings, both for exposure as well as depth of field, motion blur, and noise levels.

Have you used the exposure triangle, or do you still use it today? Please share your experience with this little graph, and how you use it in the comments below.

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Alexander Petrenko's picture

Isn’t it just a catchy name? Like «holy trinity of lenses» or «3d pop»...

Nando Harmsen's picture

Something like that.

Alex Reiff's picture

I can't recall ever hearing anyone say that the exposure triangle was a useful diagram for exposure calculations, just that it's a quick way to demonstrate that the three exposure controls are interrelated. We could just as easily call it the exposure trinity or the exposure trio and get the same point across, or use something more accurate but more confusing like the exposure cuboid, where we convert every control to a length and have photographers calculate the volume.

Nando Harmsen's picture

You would be surprised how many photographers like to approach the exposure scientifically :)
The exposure cuboid? Is this a joke, or something 'real'
I do remember something with flash exposure incorporated...

Alex Reiff's picture

That was mostly meant as a joke. The only thing I can think of that's related to flash exposure is the inverse square law.

Nando Harmsen's picture

I like that joke a lot... I am going to see if I can make something out of it. Would be nice to use in future presentations

Matthias Kirk's picture

I mean, as a beginner you are encouraged to "study the exposure-triangle". I wasted quite some time before I realized that it means nothing more than that the exposure is affected by SS, ISO and F-number, something if figured out in the first 5 minutes of the learning curve. The existence of the term implies that the "triangle" is some sort of tool or concept like the zone-system or the color-wheel, for example. I believe the term only exists so that people can feel good about themselves, because to the laymen it makes things sound far more sophisticated than what they really are.

Nando Harmsen's picture

Good point. It makes photography sound really scientific and complex :)

Alexander Petrenko's picture

Exposure pentagon: iso, shutter, aperture, flash power, distance to a subject.

Jerome Brill's picture

The exposure triangle is just a diagram. If you want to represent a single thing that three options have in common it's the easiest visual explanation. Although it can be confusing when people try to correlate how these settings work together while looking at the diagram. It's not for that and any time someone tries to fit that information within the diagram is becomes more confusing. It's not a great way to teach the other settings individually and how they will change your photo.

Nando Harmsen's picture

True. It is confusing. The downside of these diagrams is, you need to learn some people to ignore these diagrams first, before you can teach them how it works in reality

Tim van der Leeuw's picture

What do you mean by "using the exposure triangle"?

I don't look at a diagram of the exposure triangle and I don't look up tables with equivalent exposures. With digital, the camera does that for you continuously.
With film, the light meter does that for you.

In the backs of our minds I guess we all apply the rules of the exposure triangle when adjusting our camera settings to get the desired amount of light on a photo, in combination with our histogram and what the camera considers the "ideal" exposure.

Nando Harmsen's picture

I agree with you. Our cameras do all the math.
Still, some photographers keep thinking the best way of exposing a photo is by doing everything manually. They think it is the only way to control the light... and for the same reason they look at the exposure triangle...

Steve Gould's picture

Seriously, if you can't do most of these calculations in your head while looking through the viewfinder you need to practice. Call me old school, but this was common knowledge in the days of film when you had to know what an image was going to look like before you pressed the button.

Nando Harmsen's picture

Yes indeed. As I said, I never knew this existed until the digital era. Back then you had to know about these things. Now we look at the screen and dial the settings until it looks right.

John Herzel's picture

What an overly complicated way to explain a simple concept. I think Ansel Adams' "zone system" is easier to explain to a beginner, than applying plot points to a triangle graphic. Now superimpose corresponding triangles (with ISO, shutter speed, and aperture settings) for approximately 16-22 ev (light meter readings/exposure values) that your camera can recognize and tell me if this makes it any easier to explain or use. 😂And please understand that this is NOT criticism of the article, but rather the mental gymnastics required to explain and use the plotted triangle as a graphical tool to calculate/ explain proper exposure to another human.

Nando Harmsen's picture

People tend to make thing more complex than needed. This is a good example. :)

Francis Drake's picture

This is insanely over complicated.
Just remember how your camera works :
- the hole size gets more or less light in
- shutter speed let's you integrate more or less that light
- iso is just a gain that you can apply to the result

Nando Harmsen's picture

That is the theory. Now apply this in real life to have the correct exposure.

Peter Perry's picture

The “hole” allows for volume
The Shutter slices that volume into chunks of time
ISO controls how much the medium can absorb

You’re absolutely right, but I wanted to add one aspect of it.

Thinking of this in terms of flash, it helps people understand why shutter speed is a better tool to control ambient light.

Now if only people would stop being Bokeh addicts and start paying attention to depth or field, we might see more than YouTube inspired images.

stuartcarver's picture

I like the one that displays the graphics, the man running getting more blurry the lower the shutter speed etc.. for beginners I feel that’s the best visual aid to understand what each of the 3 settings is doing.

Nando Harmsen's picture

You don't need a triangle for that... but indeed. That is a nice one

stuartcarver's picture

Yeah I don’t think it will ever be useful for actually setting a camera but at least it displays what impact each setting has.

Tim van der Leeuw's picture

One other thing -- the "exposure triangle" is often presented as some sort of things that should give you answers but often without any reference to what the real starting point is for any point on the exposure triangle:

The amount of available light.

Discussion of the exposure triangle too often leaves out measurement of available light, or EV value. Are we aiming for a correct exposure at EV 14? Or EV 5? or EV -3?

Then look up what is correct exposure for that EV value -- that's how you would use the exposure triangle. Not as a thing on its own, which is how its too often presented.

I also think that quite a lot of photographers don't really understand EV and what their camera shows: I see people saying that you should "set your exposure so the camera shows EV 0".
No! Wrong!
The camera DOES NOT show you that your exposure is now at "EV 0". I have actually never yet seen in any camera interface or EXIF data the EV measured by the camera.
What the camera exposure meter shows you, is how far your current exposure deviates from what it considers the "ideal exposure". The camera shows you that your current exposure is +1 EV from "ideal", or -1 1/3 EV from "ideal".
Or 0 EV from "ideal" -- but not "EV 0".

That makes me wonder, how many (digital) photographers these days really still know what EV is? What EV 0 is? What EV corresponds to a moonlight night, or a bright sunny day?

Understand that, from there understand how to set your camera so that the resulting exposure will reflect that amount of light correctly, and from there learn to understand how the rules of the exposure triangle can guide you to find equivalent exposures that give you different effect on the photo.
Then you don't need to actually use the exposure triangle directly, you can let the camera do that, but understanding the rules of equivalent exposures is a very useful background-knowledge to have.

But for teaching anyone anything about exposure I think it's much more useful to start with teaching them about EV, and from there bridge to the correct exposure parameters for that EV, and then make the step to the exposure triangle.

I think most online materials I've read miss that first step.

Next step is then "exposure to the right" or "exposure by histogram", where you know you will do post processing on images to correct the exposure but retain detail in shadows, highlights, etc.

Nando Harmsen's picture

Thank you for your thoughts about this.
I incorporated a schematic with the different EV values belonging to the combinations in shutter speed and aperture with my e-book. This is much more valuable compared to such a popular drawing of a triangle. Unfortunately no one is looking at these charts anymore, because it is easier to dial the wheel until the image looks okay in the (electronic) viewfinder or on the screen.
On the other hand, it wouldn't be good if we would still need those charts for exposure. Nevertheless, it wouldn't harm if we all had some knowlegde of the amount of light measured in EV. It would give a head start when you go out photographing.

Tim van der Leeuw's picture

I would be interested in seeing how you have done it in your upcoming e-book!

Nando Harmsen's picture

I used it to explain how you could change settings and obtain the same exposure. Something with stops and so forth :)

Tim van der Leeuw's picture

That doesn't sound like I'll learn a lot from that chapter but I'm just curious to read eventually how you explain it, and if that would make for a better introduction than what you can commonly find online! :D

PS: Yes I realise that this will cost me some money, I'm not angling for freebies in case you wonder :D

Nando Harmsen's picture

You can check my website for the e-book. It is in Dutch, but I guess that is of no issue for you ;)

Tim van der Leeuw's picture

Hoe heb je dat geraden :D

Ik kreeg trouwens de indruk, van hoe je jouw artikel had geschreven, dat je nog aan het schrijven was aan dit e-book! Vergisssing mijnerzijds :)

Nando Harmsen's picture

Nee, het is al een paar maandjes online... alleen heeft de webwinkel wat problemen gekregen die ik niet gefixed krijg :(

Tim van der Leeuw's picture

Ah misschien verklaart dat waarom ik nog geen download-link heb.

Peter Perry's picture

Almost no Amateurs know about it at all, because people who know better should stop referring to the exposure triangle, there’s truly no such thing. It was created to try and add in the variable that Auto-ISO became when it was created.

I personally know all about it, because I’ve studied it. However, cameras like the Fuji bodies do such a great job at WYSIWYG, that you could literally go for days without needing to reference it if you’re not a strobist. But this is great as well, because it truly creates an atmosphere where you can focus on the artistic side of photography more than the technical side (you do still need both).

Nando Harmsen's picture

It is not ony Fuji bodies (are you a Fujifim used?)
This is possible with all cameras with liveview on the LCD screen, and/or an electronic viewfinder.

Peter Perry's picture

The only problem with it is that ISO was never defined as a property of exposure when Friedrich Deckel created the EV system. ISO was a property defining the sensitivity of the medium and remains such today, where as Exposure is defined by the volume of light allowed to pass the shutter and strike the medium, it is literally a measurement of factors external to the camera. It is poor photography education that would lead someone to claim otherwise.

So you can call it a reciprocity triangle if you want, but technically speaking the term Exposure Triangle is factually inaccurate.

You can see evidence of this right in the camera, as your Auto-ISO setting is different from your Exposure Value Compensation dial.

Nando Harmsen's picture

This is the scientific approach. If I change the ISO, the exposure will change. Perhaps this is formally inaccurate, just as you explained, but as long the image will become lighter or darker, it will be seen as a way to change exposure.

Nigel Voak's picture

I had never heard of the exposure triangle until a few years ago.

By trail and error and reading textbooks I just learnt with the help of a light meter what happened if I wanted to increase shutter speed or use a smaller aperture for a given ISO.

My Weston light meter taught me a lot about photography.

I think the triangle is a nice tool to explain to the beginner the concept of how shutter speed, aperture and ISO interact.

Nando Harmsen's picture

Moving the sides of the triangle... That is an interesting way to look at it
Could you refer to a site that is showing this way of using this triangle?

Nando Harmsen's picture

If it can be used for teaching, it can be valuable.

Nigel Voak's picture

I have seen endless arguments about the "triangle" on the DPR forums, where the "professors" turn up and tell everybody why it is wrong etcetera. They are probably technically right, but the miss the fact that a person has to start somewhere when they pick up a "proper" camera for the first time. They miss the fact that a simple approximation even if not strictly true, can be useful at times.

I see this as a useful tool for explain to those taking their first steps in photography beyond the cell phone, how to use the various settings like shutter speed, aperture and ISO to get good pictures.

Once a person has grasped these facts they can move on to a deeper understanding of how the camera works.

Nando Harmsen's picture

I understand your argument. Do you feel the triangle gives you an understanding of the relationship and how to get a proper exposure?

Nigel Voak's picture

I think for beginners it is an excellent way of getting them started with how to control how a picture is made by manipulating the three main factors.

Nando Harmsen's picture

Three variables makes it always difficult. For beginners it is better to learn exposure, and playing with settings when there are just two variables.