My Beginner’s Guide To The Exposure Triangle. Hi and a very warm welcome to Episode 158 of the Photography Explained podcast. I’m your host Rick, and in each episode, I will try to explain one photographic thing to you in plain English, in less than 27 minutes (ish), without the irrelevant details. I’m a professionally qualified photographer based in England with a lifetime of photographic experience which I share with you in my podcast.
First – here is the answery bit
The exposure triangle is the combination of three camera settings, aperture, shutter speed and ISO, used to get a correct exposure when taking a photo. The exposure triangle allows photographers to use a specific aperture or shutter speed for a photo and still get the correct exposure. The exposure triangle helps photographers get the correct exposure in challenging lighting conditions.
You can listen to this episode here
Or read on – entirely up to you
Right, that was the answery bit. First a quick recap on the three components of the exposure triangle, which I have covered in the last three episodes.
Aperture
Aperture in photography is the size of the opening in the camera lens which light passes through to get to the camera sensor. The aperture can be made larger to let more light in, or smaller to let less light in. The aperture is used in conjunction with the camera shutter speed to get the correct exposure. The aperture is also used in conjunction with shutter speed and ISO to take photos with different camera settings. The aperture used also determines the depth of field in an image, which is the amount that is sharp from front to back.
That was the answery bit from episode 155, What Is Aperture In Photography? Check out the episode if you missed it and want to know more about the aperture.
Shutter speed
Shutter speed is the amount of time that the camera sensor is exposed to light. The shutter speed can be changed to allow more or less light to reach the sensor, getting a correct exposure in combination with the aperture and ISO. Fast shutter speeds freeze the action and capture fast-moving things, and are also used in bright lighting conditions. Slow shutter speeds can create movement and blur in photos and are also used in low-light conditions.
When taking photos handheld the shutter speed needs to be fast enough to prevent camera shake and ensure that you get a sharp image every time.
This is the answery bit from episode 156, What Are Shutter And Shutter Speed In Photography? Again, check this episode out if you missed it and want to know lots more about shutter and shutter speed.
ISO
ISO in photography refers to the sensitivity of the camera sensor to light. ISO is a camera setting that allows you to make a picture brighter or darker. The ISO setting helps you to use different apertures and shutter speed combinations to get the correct exposure in varying lighting conditions. The ISO setting enables you to use faster shutter speeds in low-light conditions. ISO is one of the three elements of the exposure triangle, the others being aperture and shutter speed.
The aperture and shutter speed controls the amount of light that reaches the camera sensor. ISO changes how the sensor processes the light, making an image brighter or darker.
Lower ISO settings give higher-quality images than higher ISO settings. Higher ISO settings can introduce digital noise into photos.
Changing the ISO does not change the sensitivity of the sensor.
That was the answery bit from the last episode, episode 157, all about ISO. OK, the full title was What Is ISO In Photography? All You Need To Know.
Ok, so these are the three components of the exposure triangle.
Now a fundamental point
- The aperture and shutter speed control the amount of light that reaches the camera’s sensor.
- ISO changes how the sensor processes the light, making an image brighter or darker.
So what does this all mean?
This is important, as the exposure is the amount of light that reaches the camera sensor when you take a photo. Get the exposure wrong and you have problems.
Photography is drawing with light let’s not forget.
How do I get the correct exposure?
If you are using an automatic mode on your camera the camera does this for you. And there are subject-specific automatic modes such as landscape, portrait etc.
And a lot of the time these work just fine. You can get great results using these automatic modes.
Why should I care about the exposure triangle – my camera has got this covered.
To be honest, if you don’t want to understand the exposure triangle, and you are happy letting the camera do all the work for you then that is fine. You will still get lots of great photos. But.
- There are times when your camera will not give you the correct exposure. What do you do then?
- And there are times when you will want to use a specific aperture or shutter speed.
- And you might also just want to fully understand what your camera is doing, and how.
- Or you might just want to have control of everything yourself, you don’t want your camera telling you what to do!
This is why you (and I) need to understand the exposure triangle.
There are times when your camera will do just fine, and times when you will need to do the work yourself, either because you want to, or because the camera can’t cope with the lighting conditions.
A quick reminder on camera modes
- Automatic modes – the camera selects the aperture, shutter speed and ISO. These are called Basic Zone modes on my Canon 6D.
- Semi-automatic modes – you select the aperture or shutter speed and the camera does the rest. These are called Creative Zone modes on my Canon 6D.
- Manual mode – you set everything. This is also one of the Creative Zone modes.
When I am talking about the exposure triangle, this is using Creative Zone Modes, which on my Canon 6D are
- Bulb mode
- Manual mode
- Av – Aperture value, aperture priority mode
- Tv – Time value, shutter priority mode
- P – P for program, not professional!
You cannot change the exposure settings in the Basic Zone modes on my Canon 6D, this only applies using the Creative Zone modes. Check your camera and see which modes you need to be in to be able to change the aperture, shutter speed and ISO.
Why might the camera not always get things right?
Do you know what, I am going to cover this in the next episode? Here are the main reasons why the camera might not get the exposure correct.
The camera meter is assessing the light coming through to the camera sensor, and assumes that the world is grey – it is pretty much averaging out all the light that hits the digital sensor to give what is 18% grey, also known as mid-grey or average middle grey.
Photograph a white cat in a snowstorm? The camera thinks that it is photographing a grey scene, not white, so it underexposes the snow making it all grey and horrible.
The same applies at the other end – photograph a bat in a coal bunker and guess what – the meter is fooled and overexposes the image turning all that black stuff into grey.
So the camera does not always get it right.
The good news is that the camera gets it bang on a lot of the time. We just need to be prepared for when it struggles.
Another challenging situation is when the sun is in a photo. The light meter struggles to balance the extreme range of light, and if you take a photo with the sun in it the rest of the photo will be underexposed, too dark.
More on this lot next episode ok?
Underexposed, overexposed
Sorry – should have explained these terms.
Underexposed photo
Not enough light has reached the camera sensor, the photo is too dark. You need to change something to let more light in – that would be a slower shutter speed or a larger aperture. Or increase the ISO value.
Overexposed photo
Too much light has reached the camera sensor, and the photo is too light. You need to reduce the amount of light that gets to the sensor – to do this choose a faster shutter speed, a smaller aperture, or reduce the ISO.
Correctly exposed photo
This is what we are aiming for. There is one correct exposure, one combination of aperture, shutter and ISO. One exposure value.
Choosing a specific aperture
You may want to take a photo using a specific aperture. So you select the maximum aperture, let’s say this is f/2. But when you check the camera meter reading the photo will be overexposed. So what do you do?
You have chosen the maximum aperture, which is the largest opening in the lens, letting the most light in. Your photo is going to be overexposed. You need to reduce the amount of light, which you do by choosing a faster shutter speed. Or a lower ISO.
Next, you want to take a photo using the minimum aperture, with the aperture blades closed as far as they go, making the opening in the lens the smallest. You have reduced the amount of light that gets through to the camera sensor, and your meter is saying that your photo will be underexposed. You need to get more light to the camera sensor, meaning you need to use a slower shutter speed, exposing the camera sensor for longer, or change to a higher ISO.
Different apertures give a different depth of field, the amount of a photo that is sharp. There is also a sweet spot on every camera lens, the sharpest aperture with the least optical errors. So choosing a specific aperture affects the exposure.
Choosing a specific shutter speed
Very much subject-related.
Want to photograph something moving fast? You will need a fast shutter speed. So to get the correct exposure you might have to use a larger aperture or increase the ISO.
And to create motion blur in a photo you need a slower shutter speed. So in this case you will need a smaller aperture, or reduce the ISO.
Choosing a specific ISO
Well, you should use the lowest ISO that you can. And you change the ISO, which if you are starting with a low value means increasing it, only when you have to.
Right, that is the what, so how does this lot work?
There are scales for aperture, shutter and ISO. I am not going to go through these again, you can look at these on the blog posts for these episodes which I have added links to above.
In automatic modes, the camera is doing all the work for you. I explained this earlier. Here I am talking about when you are taking photos using the Creative Zone modes.
Time for some practical examples.
You set a nice, low ISO, let’s say 400. And for completeness, you are using a 50mm f/2 lens on a full-frame camera, and are shooting handheld. And it is a nice sunny day. Ok, that is the scene set nicely.
You compose your photo.
You press the shutter button halfway, and the camera takes a meter reading. The correct exposure can be achieved using the following settings according to the camera.
f/8, 1/60th second.
You take the photo. It is too bright. So you need to reduce the amount of light, by changing
The shutter speed
You can change the shutter speed to a faster shutter speed letting less light in. That would be 1/125th second (1 stop). Photo still too bright? Then try 1/250th second (2 stops). And the photo is all lovely. Great.
The correct exposure is f/8, 1/250th second, ISO400.
The aperture
We know that a 2 stop adjustment will give the correct exposure, so all we need to do is make a 2 stop adjustment to the aperture, making the aperture smaller and letting less light in. f/8 to f/11 is 1 stop, f/11-f/16 is 1 stop.
The correct exposure is f/16, 1/60th second, ISO400.
The ISO
Want to stick with f/8, 1/60th second? Simple. reduce the ISO by 2 stops. ISO400 – 200 is 1 stop. ISO 200-100 is 1 stop.
So the correct exposure is f/8, 1/60th second, ISO100.
That works nicely. You are using the exposure triangle to get a correctly exposed photo. Not too much science to that. You are correcting an overexposed photo in camera.
And yes, I have checked this a number of times to make sure I get this right!
Right – let’s take this to the next level.
Remember, we are using F8, 1/60th second, and an ISO of 400
You take the photo, and it is too dark.
You need to change a camera setting to let more light get through to the camera sensor.
Change to a slower shutter speed, so you would try 1/30th second next. Still too dark? Then try 1/15th second. And the photo is OK, the exposure is correct.
- Changing the shutter speed from 1/60th second to 1/30th second is 1 stop.
- Changing the shutter speed from 1/30th second to 1/15th second is 1 stop.
The correct exposure is 1/15th second at f/8 using ISO100.
The problem is that the shutter speed is so slow your photo is blurry. You need to take the photo using a shutter speed of 1/60th second to get a nice sharp photo (or put your camera on a tripod).
What to do?
We need to make a 2 stop adjustment to the aperture, meaning that we go from f/8 to f/4. This is a 2-stop adjustment.
The correct exposure will be 1/60th second at f/4, which is the same exposure as 1/15th second at f/8.
And if you did not want to change the aperture, your only other option is to change the ISO by 2 stops, going from ISO400 to ISO1600.
So the correct exposure here would be F8, 1/60th second, and an ISO of 1600.
And this is how the exposure triangle works.
You use the exposure triangle to get the correct exposure, and also to get the correct exposure using the aperture or shutter speed that you want to use.
And you use the exposure triangle to correct for when the camera meter gets it wrong.
I am going to stop there before I come up with a load more examples, these should do.
There are many reasons why you would need to use the exposure triangle.
- To get a shallow depth of field by using a large aperture
- To get a greater depth of field by using a smaller aperture
- Creating motion blur by using a slow shutter speed
- Freezing action using a fast shutter speed
In each of these examples, changing one camera setting needs a change in one or two of the other elements of the exposure triangle to get the correct exposure.
Right – talky bit over – what if I use a phone and not a camera?
You can just ignore all this if you want to. I don’t bother with the exposure triangle when I am taking photos with my phone unless there is something seriously wrong with a photo. And then I just use the slidy up slidy down brightness thing to make things better.
Sure you can get into this with various apps, but I don’t – that is what I have a camera for! More on this erm next.
What if I use a film camera?
You have to get the proper exposure every time as you are using film. Every incorrect exposure will cost you money. And you won’t know if you have got the exposure right or not until you have got your photos back from processing. But get to know your camera and you get a feel for when you have to make adjustments – this is what we did before digital cameras appeared.
This is why practice is so important, and why applying a “taking photos with a film mentality” to digital photography is such a great thing to do.
What do I do?
I use AV Mode on my Canon 6D. I use ISO100. I select F8, and the camera selects the shutter speed. But, my camera is on a tripod, and I use Auto exposure bracketing (AEB).
What is this?
This is a technique where you take three (or five) different photos at different exposures and merge them together later creating an image with an extended range of lights and darks. My Canon 6D has this feature.
Think about it. Take a 2 stops underexposed image, where you have got more of the dark stuff, and then take a 2 stop overexposed image, where you have got more of the light stuff, and add in all the bits in the middle and you have captured more of the lights and darks than you can in a single image capture.
And there is nothing wrong with this.
This is what I do.
Some thoughts from the last episode
Episode 157 was What Is ISO In Photography? All You Need To Know.
What did I forget to say? Nothing, but I just wanted to remind you that the lower the ISO the better, but you need to make sure that the shutter speed is fast enough to get a sharp photo.
Next episode
Episode 159. I have covered aperture, shutter speed, ISO and now the exposure triangle, so time to move on to something new.
I quite fancy tackling crop factor next, a term that certainly needs some explaining. Shall I do that? No, I will not, I am going to look at how camera meters work and why there might be problems with getting the right exposure.
And then I will move on to crop factor.
Photography Explained Podcast Episode 159 – Camera Metering – How To Get The Right Exposure
Ask me a question
If you have a question you would like me to answer just head over to the podcast website – photographyexplainedpodcast.com/start where you can find out what to do. Or just say hi. It would be lovely to hear from you.
And it would save me from having to come up with a question!
That’s all.
This episode was brought to you by, for a change, a cheese and pickle sandwich and shock horror no crisps washed down with a nice cold Diet Pepsi before I settled down in my homemade, acoustically cushioned, technologically sound recording emporium. Today’s acoustic treatment is two pillows and two hoodies!
I’ve been Rick McEvoy, thanks again very much for listening to my small but perfectly formed podcast (it says here), and for giving me 27 ish minutes of your valuable time. I think this episode will be 27 minutes long after I have edited out the mistakes and other bad stuff.
Take care, stay safe
Cheers from me Rick
OK – that was the podcast episode.
Want to know more?
Head over to the Start page on the Photography Explained Podcast website to find out more.
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Thank you
Thanks for listening to my podcast (if you did) and reading this blog post (which I assume you have done as you are reading this).
Cheers from me Rick
