Understanding the basic operations of your camera can be overwhelming. We’ll simplify the Exposure Triangle (shutter speed, aperture, ISO). And we’ll keep it short and sweet!
Why is it called The Exposure Triangle?
Eh, why not? There are three camera settings that work together to control how bright your image is, after all. Each of the three settings regulates the amount of light that either goes into your camera sensor or film (shutter speed and aperture) and how sensitive that surface really is (ISO).
First, let’s describe each of the three elements in The Exposure Triangle, shall we? After that, I’ll use night photography examples to illustrate the relationship between them all.
Shutter speed (length of exposure)
As the name implies, this is simply how long the shutter is open.
- The longer the shutter is open, the more light reaches the sensor or film.
- The shorter the duration of time it is open, the less light reaches the sensor or film.
It’s simply the amount of time that we expose the sensor or film to light.
That wasn’t too bad so far, right?
Aperture
An aperture is simply how large the opening of the lens is. And I’m sure you are going to figure this out, but here goes!
- The larger the opening, the more light shines through.
- The smaller the opening, the less light shines through.
Open your eyes wide, then squint, and you’ll get an idea of how this goes!
ISO
ISO is amplification. It’s like the volume knob on your radio. If you crank your volume knob, you are taking whatever the incoming signal is and turning it up. If it’s a weak signal with lots of static, that gets turned up as well. CRKZZZZKT-BZZZZT!! If it’s a strong signal (with less noise), then mostly the sound is turned up. Aaaaaahhhh!
So it is with light. If you want more light — a brighter overall image — you crank the the ISO. But if it’s, say, really dark or there is otherwise a lot of “noise,” well, it cranks that up too! There’s always a trade-off, isn’t there? Lucky for us, that modern cameras handle high ISO settings much better than older cameras did.
In essence, ISO controls the sensitivity to light. The higher the ISO, the more sensitive our camera is to light. But in reality, we are boosting the incoming light in an effort to produce an image that is properly exposed. and sometimes, we need to boost that incoming light more than others.
How does knowing The Exposure Triangle help us?
Remember, the three controls of the camera — shutter speed, aperture, and ISO — all affect how bright our photo is. And they all affect each other. I’ll use some night photography examples to illustrate.
Shutter speed and how it helps us
We learned that the longer the shutter speed, the more light we let in. Makes sense, right? If we are taking a night photo, well, great! We can leave it open for a long time — even several minutes — and we have our photo, right?
Well, yes. Unless we want to “freeze” movement.
For example, if we want our stars to look like long star trails, then we can choose a longer shutter speed.
If we want our stars to look like pinpoints, then we choose a shorter shutter speed. Maybe if we have an ultra wide-angle lens, we might choose 20 seconds instead of several minutes. This is the single exposure astrophotography sort of “freezing” movement, as with just about any other form of photography, 20 seconds would be considered a very long exposure!
But now, you’re probably thinking, “Hey, if you choose a shorter shutter speed, doesn’t the image become really dark because of less light?”
And you’d be absolutely right. But we can do something about that! We can make the image brighter with aperture and ISO.
Aperture and how it helps us
Above: One of these photos requires a much wider aperture to have a shorter shutter speed and capture the stars as pinpoints.
Let’s say we want our stars to look like pinpoints of light, much like the way they appear to us at night. We’ve shortened our shutter speed so that the length of exposure is short. That stops the stars from trailing. But oh no! The image is dark!
Not to worry. We can open the aperture so that it’s big and large and lets in lots of light. We can do that by adjusting the aperture on our camera (or for some of us, on our manual lens, which works the same way).
The smaller the number, the wider the aperture. Aperture, or f-stop, is expressed as division, where you divide the focal length to find the aperture. This can be confusing. But just remember that an aperture of f/1.8 or f/2.4 is really wide, and that an aperture of f/16 or f/22 is really narrow.
So if we set our lens to a wide aperture of something nice and wide like f/2.4 or f/2.8, we let in far more light than if it is f/8 or f/10 or f/22.
ISO and how it helps us
Above: The photo on the left was photographed during a nearly full moon. I also wanted to capture the apparent movement of the stars over three hours of time. The photo on the left was photographed with no moon present. I also wanted to capture the stars as pinpoints of light. Which scenario is more likely to need a higher ISO?
Starlight is really dim. What if the short shutter speed and wide aperture still aren’t enough to capture stars as pinpoints of light?
That’s when we crank the “volume” on the light. That’s right, ISO.
The higher the number, the more we are boosting the light. ISO 200 doesn’t have a lot of boost. ISO 4000 has a lot. And ISO 102,400 probably looks like a cheap security camera during a snowstorm!
Now, just like music, you don’t want to crank it too much. If we play music too loud, we lose definition and detail. It can become distorted and sound lousy. So it is with ISO and light as well. If we crank the light too much, we can get more noise and lose definition and detail by being too bright.
Maybe our sweet spot is somewhere around ISO 3200 or ISO 4000 for a Milky Way photo. It depends on numerous things, such as how bright the surrounding area is. But it also depends on two other friends of The Exposure Triangle, shutter speed and aperture.
Yes, there’s more!
This is the “extra credit” part of the article!
There’s far more to camera settings in The Exposure Triangle than my simple explanation, of course. After you get the hang of it, you can take a deeper dive into other aspects of The Exposure Triangle and experiment. Below are a few examples!
How else can we use shutter speed?
Shutter speed can be used to freeze subjects that are moving. Think about photographing sports or dancing. You can widen your aperture and boost your ISO to help achieve a faster shutter speed. See how shutter speed, aperture, and ISO are interrelated? See how they can help you do what you want to do?
How else can we use aperture?
Then there’s aperture. Yes, the wider your lens opens, the more light it lets in. But there’s other reasons to use a wide aperture as well.
For instance, some photographers might do this to separate the subject from the background by creating a shallow depth of field. This would make it so only the subject is in focus.
And some photographers might use a smaller aperture to create a wide depth of field and have a lot more in focus.
Here’s the cool part. You already know this intuitively! If you try to see things more in focus, you will sometimes squint your eyes. Not bad, eh?
You can learn more about this by reading “Photography 101: Why do I want to control depth of field?”
How else can we use ISO?
ISO amplifies incoming light. But it can also amplify noise. Or make things too bright. But like the other two, it helps us control how bright our image is. Raising ISO allows us to shorten the shutter speed. Or it might let us choose a smaller aperture.
One could write quite a few chapters of a book on The Exposure Triangle. However, the main point of this article is to describe The Exposure Triangle so you understand what each part does. It affects your image no matter what kind of photography you do. Hopefully this article helps!