What Is The Exposure Triangle? (Revisited)
The exposure triangle is the combination of the camera shutter speed, aperture setting and ISO. The camera's shutter speed and the aperture setting control the amount of light that reaches the camera sensor when you take a photograph. The ISO controls the sensitivity of the camera sensor to light. When applied correctly, these settings will enable a correct exposure to be achieved.
The exposure triangle can be used creatively to take correctly exposed photos with different aperture, shutter speed, and ISO settings. The exposure triangle is also used to take photographs in challenging light conditions, and also for creative image capture.
Hi, everybody, welcome to Episode 27 of the Photography Explained podcast. In this episode, I again ask the question, what is the exposure triangle?
I'm your host, Rick, and each week I try to explain one photographic thing per episode to you in plain English in less than 10 minutes without the irrelevant details. My aim is to explain things in just enough detail to help us with our photography and no more.
You can listen to the episode here
Or you can read on - it’s entirely up you!
Now the bit I was getting stuck on was defining the exposure triangle, which, looking at my notes, is still wrong, but I managed to correct myself there. I'm going to come back to that.
The exposure triangle is a combination of shutter speed, aperture and ISO. I'll say that again in English. The three elements of the exposure triangle are shutter speed, aperture setting, and ISO. The shutter speed and aperture control the amount of light that gets through to the camera sensor, and the ISO controls the sensitivity of the camera sensor to light (in theory).
Okay, that's it, I'm sort of happy with that. I don't mind making mistakes (as long as I notice them that is!). I'm human and I'm not reading this entirely from a script. I do have prompts in front of me and you'll see why in a minute.
So that's the easy bit out of the way. And this is why in previous episodes I explained aperture, shutter, and ISO individually.
The aperture scale
So let's remind ourselves of the aperture scale. This is the aperture scale, these are full stops.
F1.4, F2, F4, F5.6, F8, F11, F16, F22.
Each step on the scale is one stop. A stop is a doubling or halving of light.
The shutter speed range is this
1 second, ½ second, ¼ second, 1/8th second, 1/16th second, 1/30th second, 1/60th second, 1/100th second, 1/250th second, 1/500th second, 1/1000th second, 1/2000th second, 1/4000th second, 1/8000th second
Each step is one stop, I stop is a doubling or halving of light.
The ISO scale
100, 200, 400, 800, 1600, 3200, 6400, 12800, 25,600
Again, each step is one stop. A stop is a doubling or halving of light.
So what does this all mean?
Surely, there must be a better way because I've really struggled to explain this. So I'm now going to try again and then I'm going to wrap this up - I don't want to get too deep into this one because yeah, it's one of those, isn't it?
If you're using the following camera settings
Shutter speed 1/250th second
Aperture f8
ISO 200
And your camera is saying that this is the correct exposure.
What happens if you change the shutter speed?
If you change the shutter speed to 1/125th second you are doubling the amount of time the shutter is open, doubling the amount of light reaching the sensor.
That will result in an image which is overexposed by one stop as in too bright because too much light has got in.
Now then, if we go from 1/250th second to 1/500th second, that's half the time the shutter is open, which is half the light reaching the sensor, resulting in an image which is underexposed by one stop, which is dark.
What happens if you change the aperture?
Back to the original settings
Shutter speed 1/250th second
Aperture f8
ISO 200
If we change the aperture from f8 to F 5.6 we're doubling the amount of light getting to the sensor, resulting in an image which is one stop overexposed and too light.
If we go from F8 to f 11, we are halving the amount of light meaning that the image is underexposed by one stop, and is too dark.
What happens if we change the ISO?
Shutter speed 1/250th second
Aperture f8
ISO 200
If we change the ISO from 200 to 400, we double the sensitivity of the sensor, resulting in an image which is overexposed by one stop. If we change the ISO from 200 to 100, we're halving the sensitivity of the image sensor resulting in an image which is underexposed by one stop.
Note - we are not actually changing the sensitivity of the sensor - we are changing the brightness of the image.
Did this make sense?
Right? that's it in a nutshell. So you change one of these things and it overexposes or underexposes the image.
Why this matters
You can change two things, you can increase the shutter speed by one stop which is halving the time the shutter is open, but if you also open up the aperture by one stop, doubling the light, you will get the same (correct) exposure.
Creative control
This is the point. You can change two of these things or all three, which means that you could use the aperture that you want to use for a photo
If you want a shallow depth of field, or a lot of depth of field pick an aperture and change the other settings to get the correct exposure.
Or if you want to use a fast shutter speed or a slow shutter speed do the same.
That's the exposure triangle - the relationship of the three things aperture, shutter, and ISO. And I'm hoping that now you understand that if you change the shutter speed by one stop, you need to change the aperture by one stop to get the correct exposure.
Dealing with an incorrect exposure
Now it might be that the exposure that your camera is telling you about isn't actually correct, because the camera cannot see as much as our wonderful eyes can.
You might take a photo and because of the conditions and the way the light is your camera overexposes the image. In that case, you would adjust the shutter speed or the aperture ordinarily, to reduce the exposure so you'd go the faster shutter speed or a smaller aperture to reduce the amount of light getting in to get you to a more correctly exposed shot.
This is creative photography, and this is why the exposure triangle is so important.
You don’t normally change the ISO through choice, you change the ISO through the necessity of the other settings and the lighting conditions. If it was darker and you needed a faster shutter speed you would raise (push) your ISO.
It's well worth spending time on this and learning it properly (through practice) because everything that you do going forwards will be influenced by the exposure triangle. So I hope this has made sense.
Next episode
What’s next? In the next Photography Explained Podcast - well I have had a change of mind. I am going to come up with some practical applications of the exposure triangle. OK? The title is being worked on right now. And here it is! Photography Explained Podcast Episode 28 - 5 Practical Applications Of The Exposure Triangle
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Okay, thank you for listening. And I hope you've enjoyed this episode. This was a tough one. I'm glad I got through it. I think I'm going to find something a bit lighter for the next one. But if you did enjoy it, please leave a nice review and rating wherever you get your podcasts from. And please subscribe so you don't miss an episode.
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I've been Rick McEvoy, thanks again for listening and giving me 10 minutes of your valuable time. And I'll see you in the next episode.
Cheers from me, Rick