What Is the Exposure “Quadrangle”?

In Master Photography Roundtable by Jeff Harmon3 Comments

Jeff and Brent discuss the exposure “quadrangle”, what it is, and why it goes beyond the traditional exposure triangle.

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In this episode we are going to start off with an article from our friends over at petapixel.com by Edward Crim.  Edward is the director of the St. Louis Photo Authority and a photo instructor. His article was titled “It’s the Exposure Quadrangle, Not Triangle” and we will put a link to it in the shows notes.  

Jeff: Before we get into Edward’s argument in the article that we need to think about 4 factors as we consider exposure, I think we need to talk a little about the exposure triangle first.  Brent, you teach photography at a college, take a minute here and tell me about how the exposure triangle fits into your instruction.

Brent: It’s all about helping photographers understand what they need to do to get a proper exposure, and what controls the camera gives them. So we look at one at a time. Initially I tell them to just set literally WHATEVER settings are necessary to get that little “dot” on the center “zero” mark which is their light meter. Just to keep moving the settings until they get that magic zero.

Then we dive into what the numbers actually mean. So I take an approach that allows them to simply get familiar with the camera and it’s knobs and buttons first, then we start working on that knowledge of where the controls are for their camera and we start talking about the specific items which are Shutter, Aperture and ISO.

Since we tend to adjust ISO the least, I start there. I give them tips on what to set for which type of lighting such as outdoors bright and sunny, cloudy or indoors. Then we go to aperture and talk about that with other lens related items and then we talk about shutter.

Shutter, in my experience, seems to be the most revealing to students, in that they can control time. If they can become masters of shutter control they see the power of that so I like to leave it for last as it relates to understanding what it really does and how to predict what it will do for our given subjects.

But really, all of them need to be controlled at the same time so they’re all being manipulated, but the understanding of what each is and does is looked at separately.

It’s All About the Light

Jeff: I want to read a paragraph from the article because it is one that made me stop as I was reading it and immediately share it back out on social media.  Edward writes:

“Some of these articles [talking about the exposure triangle] are obscure and pedantic and, as my friend Shaw would put it, indulge in technobabble to impress the reader with the writer’s expertise. Others make a sincere effort to communicate important information to the reader, but all of them fail to acknowledge that beyond ISO, aperture and shutter speed, there is a fourth part of the exposure equation, the part without which there would be no exposure at all; and that part is light.”

Brent, I am sure a lot of the listeners would say that the first part of that quote applies to me a lot as the geek at the roundtable who literally thinks non-stop about technobabble, but give me your first reaction to what he is saying there.

Brent: For me, this is when the Zen of photography starts to set in. And this is the reason I LOVE photography. I love the techno stuff too. And photography has a bunch of that. I also love the art. And what we’re talking about here is getting the techniques figured out so that you can then master them, control them to achieve your point with the light you are given, or in the case of flash photography, the light you can bring to the subject.

But it’s also one of those “forgotten” subjects as it were. Of course we need light to have photography. That’s the whole point of the PHOTO part of the word photography. However, we take it for granted all to easily, that’s how I interpret what the author is saying here.

Jeff: In the article Edward continues to argue that back in the 1930s and 1950s as photographers were pursuing correct exposure they used tools like exposure meters and printed lookup tables like the Kodak Master Photoguide to help them make know which ISO film they needed put in their camera for a specific shutter speed and aperture for a given level of light.

I want to stop for just a moment there and say that while Edward didn’t really state it directly in his article, you could take away from his wording here that he is saying digital cameras has ruined photography.  The ability to chimp on our cameras immediately after taking a shot and look at the exposure to adjust the exposure triangle that is so talked about has made a generation of photographers uneducated about light.

But that isn’t what I took away from the article.  I don’t think he is saying we aren’t real photographers if we have never shot film, don’t have or use a light meter, and we don’t carry a printed book with tables to give us the exposure triangle settings.

I took away from his article that photographers who are so lucky to live in this digital age that has made the art of photography so much more accessible than it was in the past could benefit from a much better understanding of light.  He argues that light is actually the very most critical component of exposure and really understanding light makes it much easier to understand how to use your camera as a tool to record that light as you create your photo. Something I agree with completely.

The technology aspects are always going to be there with digital photography because of the foundation of technology you have to use in order to even take a photo.  So the technology will always be important, but getting beyond the technology so that it is not dominating your thoughts as you shoot so that you can focus on the design and artistic elements is essential.  Understanding light and how to react to it using the controls on the camera is the first big step there.

What is the Exposure “Quadrangle”

Jeff: Now that we have talked about why we as photographers should consider light as part of the equation for getting good exposure, Brent I want to get your thoughts on what exactly it means then to have an exposure quadrangle instead of triangle.  What does it mean to consider “light” as part of getting a good exposure. Maybe you can walk us through it using his really good example of the “Sunny 16 rule”

Brent: Sure thing.

By taking light into the equation, or maybe it’s better to say, we also consider it first and foremost, it will guide our decision making process. With the sunny 16 rule, the idea is that on a bright and sunny day, we set the aperture of the camera to 16, and base the shutter speed on our ISO. So if we have 100 ISO we use 1/100th of a second for the shutter.  For most sunny days here on planet earth, you’ll get a decent exposure with those settings. It’s an excellent starting point for sure. So what we’ve done here is we took light into account first. Again, I think we almost always do this, and this is a very simple approach but it helps us illustrate the point and purpose of what we are talking about.

In other situations we’ll react differently depending on how much light we’re talking about.

Jeff: Brent I want you to help me with another sentence from his article and what it means for us who are using digital cameras.  To set this up a little I think we need to bring it to a more concrete example. One that I have been in many times.

Let’s say you are shooting an outdoor sporting event a couple of hours before sunset.  You are wanting to freeze the action, which means a high shutter speed. We want background blur if we can get it, so we are opening the aperture as much as we can.  Traditionally, in the exposure triangle, we then have the ISO left and with digital cameras we want to keep that ISO as low as possible to get the very best image quality.

With a bright sunny situation we can probably take that shutter speed up to 1/8000 of a second, possibly open up to an aperture of 4.0, maybe 3.5 or 2.8, and then we will set the ISO to 100.  We have enough light to make that work. You start dialing in the settings using the light meter built in the the camera, take a test shot, and even check out the histogram of the shot and confirm you have some good exposure settings.

After shooting the event for a bit some nice fluffy clouds roll over.  They aren’t going to cause rain, but there is enough of them that it has changed things from that bright sunny light into a very overcast situation.  That’s our specific example here.

Now let me read a sentence from Edward’s article and I would like your help with that specific example and what you think he is saying in how to react to this situation:

“If clouds roll in and your light fades, .. that fourth part of the Exposure Quadrangle requires readjustment of the other three and a new EV will reign.”

Brent:  That’s exactly right. One has been adjusted, so at least one of the others must also be adjusted to get what we’d consider a proper exposure. The quality of the light is also now very different. You won’t have the deep filled in shadows you had with the bright sunny light. Things will “open up” a bit. So you you could just increase you ISO to accommodate since you don’t need to worry so much about the dynamic range and pulling out the maximum information you can out of that sensor since the difference between brights and darks are less. But that’s additional thinking that comes with experience I guess. You’ll still run the risk of digital noise build up, so make the decision that’s best for you and the needs you have at the moment. I tell my students, what would you rather deal with, a bit of noise, or missing the shot? Because that’s what it really comes down to sometimes. If you’re shooting sports and your goal is to freeze the subject and you think to yourself “I can slow down my shutter a bit”… Well, can you? Maybe you’ll not achieve the point you’re going for so ISO or aperture adjustments are needed in that case to keep the subject frozen.

Jeff: So the exposure “quadrangle” means that we are including the level of light in our scene as part of the consideration for setting up the camera to record that light.  Instead of trying things out in setting up the traditional exposure triangle with aperture, shutter speed, and ISO we think of it from the light perspective first and then dial in settings based on our creative vision.

If we are outdoors with plenty of sunlight the challenge may be how to limit how much of the abundant light reaches the sensor to accomplish our creative vision.  If we are doing a Milky Way shot then we have the opposite problem, we have to work within the limitations of the camera in order to get enough light into that sensor so that we can create the vision.

To me this is the mark of a “good” photographer.  It isn’t the equipment you have or how good you might be at recording the light of a scene with a good exposure.  Anyone can really learn most of that relatively quickly. Anyone can figure out that if you increase the shutter speed you get less light and if you decrease you get more light to that sensor.  A good photographer starts with a vision, which includes lighting that contributes to that vision, and uses the 3 elements we traditionally think about in the exposure triangle last.

You hear so many photographers who produce really good results talk about “good” light, but rarely do I hear them define what they mean by “good”.  I think this article has helped solidify in my head how to communicate that to other photographers. “Good” light is the light that is going to help you create the creative vision you have for your photo.

Even better when you can use artificial light to take complete control over creating a photo that matches your vision.  In portraits this is the biggest part of the magic photographers who can incredible results are doing. They control the light so that is always “good”.

Midroll: We are going to talk about light meters and an argument Edward makes about how the exposure triangle is insufficient in a moment, but first we need to thank a sponsor of this episode: ROYAL CANVAS

Is a Light Meter Required For Quadrangle?

Edward talks a fair amount about the various light meters he has used over the years, and I took away from his article that he is arguing an external light meter, one that measure incident light very differently from the reflected light meter in your camera, is pretty critical.  That external light meter is going to give the EV of the environment and you have a tough time really considering the “light” piece that makes that exposure triangle into a quadrangle.

Do you think that is true Brent, if we don’t have a light meter and really want to work with light as one of the factors do we need to go out and get one?

Brent: That’s absolutely true. An incident light meter is simply a light meter that measure the light falling onto the subject, not reflecting off it. So the tonality of the subject is irrelevant when you’re using an incident light meter. That’s the type of light meter we use in the portrait studio too, so you can measure the light falling on the subject, and we even get picky as can measure light falling on one side of the subject vs. the other side of the subject.

There’s a few ways to overcome this. Even though the light meter in your camera is the reflective kind that is very different from what is described in the article, it is still a good tool for finding the starting point as you are using the camera as a tool to capture light.  

You have to know how to use the light meter (check out Jeff’s Photo Taco episode “Metering Explained”) in the right way so that you can have it be an effective tool, but it is possible.  Especially if you approach it in a similar way to the zone system that Ansel Adams taught where there are 11 zones, starting at 0 where there is no light and everything is pure black up through zone 10 where there is so much light that everything is pure white.  If you use spot metering and then target the highlights in the scene to be the white you want in zone 9 and meter accordingly then it can be a very effective tool.

After you have that starting point using the light meter in your camera you can take it a step further and use the histogram (check out Jeff’s Photo Taco episode “Histograms Explained”) to fine tune your settings for the exposure you want that realizes your creative vision.

Jeff: I also don’t think that you have to use a light meter external to your camera to approach exposure using the “quadrangle”.  I think if Edward was with us on the podcast he is likely to argue that it is, but I agree with what you said there Brent. We have the tools we need in our cameras in order to respond to the light of the scene and have that inform us as to the settings we need to use to get the right exposure for our creative vision.

There isn’t a massive downside to getting an external light meter, other than maybe the cost and the time you are spending to use it.  But we have the advantages with digital to help us accomplish the same thing without having to go to an incident light meter. It takes practice and playing around with the tool until you understand exactly how it works.

In fact, that brings up another point I didn’t intend to make but I will here.  I think the constant desire photographers have to upgrade to the very latest body can negatively impact their ability to realize their creative vision.  As you use your camera you really come to understand the capabilities and limitations it has. You do that enough and you spend less and less time focused on the settings you are using and how to change them and give your brain more of an ability to focus on the things that are going to really make your shot great like the composition of the photo.  There is some value to sticking with the same gear for a while so that you can really start with the light and work through the things that are actually going to matter with your shot.

Is the Exposure Triangle Flawed?

Jeff: The last thing I wanted to go through in this episode is to talk about Edward’s statement about the exposure triangle and I want to get your reaction Brent to his statement:

“The ‘exposure triangle’ concept is flawed not only in that it overlooks the most important ingredient of photography, but it is also flawed in that the sides do not correlate in any meaningful way. In other words, they don’t tell you what exposure to use, which makes it, well, by definition, rather useless. It only deals with the camera controls and does not deal with light level.”

Brent: I don’t think I’d go so far as to say it’s flawed. It does a good job at helping photographers understand the relationship between the three basic controls on the camera. I like the quadrangle approach because of how important light obviously is. But to say this is flawed… that’s a stretch in my opinion. And here’s why.

We have to start somewhere. We end up making uninformed decisions when we first start out with photography and we mess up. And we learn. And then we start making informed decisions as it relates to the settings based on the light and then we grow and start coming up with other adjustments to achieve our creative intent. To suggest we need a system that needs to tell us where to start… well, that’s what teachers are for 🙂 (shameless plug of the day) But really, anyone can be a teacher in this respect. If you don’t know something please don’t be afraid to ask. And when you know something please feel free to share it with those that need it 🙂

Jeff: I agree again Brent.  I don’t think the exposure triangle is flawed in this way because as it is taught the concept of using the light meter inside your camera is always taught with it.  The idea then that the triangle doesn’t tell us exactly how to use the settings of the camera to get a good exposure would be true if we didn’t pair that with the light meter in the camera, but we almost always do.

He does go on immediately after that statement and admit that the exposure quadrangle is similarly flawed because it alone won’t tell you what your settings should be for a given EV.  The solution he recommended was something called Andy’s Handy Exposure Calculator from Andrew Lawn. You can download a free PDF that after printing you can cut out and glue together to make a little slide rule looking thing that shows you what shutter, aperture, and ISO to use for specific EV.  We will put a link to the PDF show notes.

What do you think of Andy’s Handy Exposure Calculator Brent?

Brent:  That’s cool. And could be very helpful. I may use it in class 🙂

Jeff: I think this physical exposure calculator is pretty limited in comparison to the tools we have in our cameras already.  Not all of the aperture, shutter speed, and ISO settings are there, plus you really have to use an incident light meter to have a chance at using this thing.  You start by measuring the EV of the scene and that only comes with an incident light meter external to your camera.

I guess I don’t really understand why this thing is any different than using the light meter in your camera and adjusting your settings based on the information it is providing.  The process is a little different, but you are using a light meter to help you find the starting point on the settings you are going to use and you have to decide based on your creative vision how you are going to change those settings to realize that vision.


Jeff: Anker PowerPort Power Strip ($35).  12 outlets, with 8 of them perpendicular to each other.  Solves a problem for me because I have a lot of things I plug in where the end of the plug going into the power strip is so big it covers the next outlet and makes it unusable.  Plus it has 3 IQ USB ports to charge up devices fast. Been a perfect addition to my office.

Brent: Perfect Exposure by Michael Freeman



  1. Great show! I really enjoyed the discussion. Regarding your discussion on the last comment that the exposure triangle is flawed, I have the following thoughts: For any given level of light (EV), there could be multiple different combinations of ISO/shutter speed/aperture that would allow you to reach a “proper” exposure. In other words, any given level of ambient light has multiple exposure triangles that could achieve a “proper exposure” but maybe only one that will lead you to create the image you want to create. So the triangle is not inherently flawed, but some triangles might produce a better photographic result for a given lighting scenario or subject. Your job as a photographer is to determine which of the many possible combinations (triangles) will allow you to achieve your photographic vision.

    1. Author


      Thanks so much for listening. I agree, the exposure triangle is still a good way to think about things and it is those who can figure out how to work with the 3 controls to achieve their vision who get the best results.

  2. Hi there ! I don’t know if you guys are aware of that book about exposure but I think you might take a look at it. I borrowed it at our public library lately as a novelty and, as a 30 years + amateur photographer, I am amazed by the way this book explicitly explains photography.

    Keep going with your podcast ! You guys are the best ! https://www.fredaldous.co.uk/products/exposure-book

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