Welcome to the first in a series of lessons designed to help you learn photography. This lesson is all about the exposure triangle. It’s going to be quite theory heavy but it’s a really important topic that will help you no end in your photography.
Why Should I Learn the Exposure Triangle?
The reason why I want you to understand the exposure triangle is, for me, it was the single most pivotal moment in learning photography. It suddenly gave me the theory that I needed to know to create the photographs that I wanted.
When you take a photograph in automatic, the camera takes a guess at what it thinks you’re trying to achieve. And sometimes it does a decent job and others it’s way off the mark. I remember when I got my first DSLR camera – I thought the photographs it took on automatic were amazing! But it didn’t take long to realise that it just didn’t create the photographs that I wanted it to take. So I’m here to help you to take control of your camera and to create the images that you really want to.
The first thing we need to do is to understand exposure. Photography is all about light. When you take a photograph, light comes into the camera through the lens and it hits the sensor, then the camera processes that light and turns it into the photograph that you’ll then see on the back of your camera.
If too much light enters the camera, then your photograph is going to be overexposed – or too bright. And in extremis, this is what you’re going to see: a completely white photograph with no detail.
If you’re not letting enough light into the camera, then your photographs are going to be underexposed or too dark. And again, in extreme conditions, if you’ve not let any light into the camera, then all you’ll get is a black image.
These are extreme examples of what you’ll see if you really mess up your settings, but it illustrates the point. Here’s an example of exposure in practice:
On the left hand side, you can see that the trees in this snowy scene are very black and you can’t make out any of the detail in the bark. The white snow also looks really dingy and grey. This part of the photograph is underexposed.
As you move across the image towards the centre, you can see that we’ve got detail in the highlights, the brighter elements, and also in the shadows, the darker elements. That’s generally what we’re looking for in a correctly exposed photograph.
Moving on to the right hand side, the photograph is now overexposed because you can’t see any detail in the sky or the snow because they’re so bright that they appear completely white. The shadows also look really washed out.
The Exposure Triangle
The exposure triangle is what helps us manage this. It helps us to understand the settings that we need to use to take the photographs that we want, and work out how to adjust our settings to achieve the correct exposure for our photograph.
The shutter speed dictates how long the camera’s shutter is open for. The shutter opens as you take the photograph, and when the exposure is complete, the shutter will close again. You might have a shutter speed where the shutter opens and closes again in a fraction of a second or you might set it to open for much longer.
Shutter speed controls how movement is portrayed in your photograph. If your shutter is only for a very short fraction of a second, then that will capture your scene exactly as it was at that moment.
In this photograph, you can see a wave crashing and all the individual droplets of water that are being splashed into the air are captured perfectly. If you kept your shutter open for a little bit longer, it would capture that droplet in one position, then another, then another and another. Your photograph would then show what’s known as motion blur, as you can see in the second photograph where the wave appears silky soft. These photographs were taken just seconds apart with different settings.
Shutter speed is also used to counteract the motion that we create from hand-holding our camera because we’re human and we can’t stand perfectly still. Too slow a shutter speed when we’re not using a tripod is going to introduce motion blur known as camera shake.
As well as controlling motion, the shutter speed will control how much light is entering the camera. So, the longer the duration of your shutter speed, the more blur you will introduce with any moving objects within your scene and the more light that will enter the camera.
The shutter speed is denoted by numbers as fractions of a second. So if you see 25, that means 1/25th of a second. Similarly, 500 means 1/500th of a second – which is a hell of a lot faster.
It is possible to have shutter speeds that are longer than a second as well and these will be denoted by inverted commas, for example 2.5 with the inverted commas means 2.5 seconds.
The diagram at the bottom of this slide is part of a cheat sheet created by Daniel Peter from Fotoblog Hamburg and it gives you a rough idea of how the different shutter speeds affect your photographs. So you can see on the left hand side, if your shutter speed is 1,000th of a second, you may well get a nice sharp image. But moving across to the right hand side with a half second exposure, then you’re going to create a lot of motion blur with moving objects in your scene. Now, this is just a rough guide and it does depend on other elements, but it’s a good guide to get you started.
The aperture is the opening created by the lens diaphragm when it physically opens and closes. This example shows a narrow aperture.
The purpose of the aperture is to control the depth of field – or how much of your scene is in focus. The diagram here shows how, as the aperture increases in size and the corresponding f-number decreases, the photograph’s depth of field is narrowed. So on the left hand side, you can see that, when you use a very narrow aperture, the figure and the scenery behind him are all sharp and in focus. As you move along and use wider apertures, the depth of field changes so that only the figure is in focus with the scenery behind him blurred out. The wider the aperture, the more light that will enter the camera.
How much depth of field you have in your photograph is part of your creative decision and you use it to tell the story that you want to tell. Most of the time, when you’re taking a portrait photograph, we want the focus to be on our subject and not the background, so we choose a narrow depth of field that just has them in focus with everything else blurry.
You can see some examples of depth of field at work here. With the portrait photograph shown on this slide, I’ve used a very wide aperture and that’s caused just a very thin sliver of the photograph to be in focus, with my eyes nice and sharp and everything else forward of that is out of focus or blurry.
With the image on the right hand side, that narrow depth of field just wouldn’t work. The purpose of this image is to show the landscape as a whole and so I want the focus to be on the entire scene and not just a single element. To achieve that, I’ve used a much narrower aperture.
So you can see how important the aperture is to your creative decision making. But each time you make the decision to widen or narrow your aperture to achieve your desired depth of field, you’re affecting the amount of light that is entering the camera.
It can be confusing to remember, because to achieve a wide depth of field we need a narrow aperture and vice versa, so an easy way to remember it is:
- The higher the f-number that we choose, the wider the depth of field – or the more that is in focus.
- The lower the f-number that we choose, the narrower the depth of field – or the less that is in focus.
With wider apertures or lower f-numbers we’re going to be letting a lot more light into the camera than with a narrower aperture (or higher f-number). So we need to balance this out with the other settings on our camera in order to keep our photograph correctly exposed. If we’re letting lots of light in with a wide aperture, then we need to compensate by using a faster shutter speed.
I’ve purposely not talked about ISO yet, because when we’re taking a photograph, ideally we only want to be changing the aperture and the shutter speed. But this isn’t always possible, as I’ll explain now.
If your image is still too dark after you’ve adjusted your shutter speed and aperture, you’ll need to change your ISO. The ISO, in olden days, referred to the sensitivity of the film that we placed inside our cameras. If we bought a roll of film with a higher ISO, it would be better suited for shooting in dark conditions and therefore would create brighter images than if we’d used a lower ISO film.
In modern, digital terms, choosing a higher ISO setting amplifies the light in your photograph to create the same effect. it doesn’t change the camera’s sensitivity as is commonly thought. The problem with this amplification of the light in your photograph is that it introduces imperfections in the form of grain or noise. Take a look at the photograph on the right hand side and you can see how grainy the cot looks behind my little boy. This is because I’ve used a very high ISO.
ISO is denoted by numbers such as 100, 250 or 1000. You might also have high or low settings which equate to a certain number. Typically your camera will have a base ISO of 100 but it may go down to 50 and this is where, ideally, like to be.
Again, using the diagram at the bottom, you can see how the higher the ISO setting that you use, the more grain you introduce – and the brighter your photograph will be. So now it’s easy to understand why we want to avoid increasing our ISO where possible as the quality of our photograph is going to be reduced.
After we’ve chosen our aperture setting to create the depth of field that we want and chosen a shutter speed to match – but we’re still not letting enough light into the camera, then that’s when we’ll be forced to use a higher ISO and just accept the reduced image quality.
There is also another option, of course, if we don’t want to introduce noise to our images unnecessarily and that’s to use a flash, but that’s something I’ll cover at a later date.
The exposure triangle gives us the underlying knowledge that we need to take the photographs that we want to take, all the while remembering that every time we change one setting, we’re going to have to compensate with the others in order to get a correctly exposed photograph. So, now you know that if you’re taking a picture of a person and you want a narrow depth of field with only a small part of your scene in focus, you need to use a low f-number. You also now know that having that low f-number means a wide aperture and that’s going to allow lots of light into the camera – so we need to compensate for that with the shutter speed. But if it’s still too dark and we can’t get more light in using our shutter speed because we’re already at the slowest setting we can use to avoid camera shake, then we need to resort to increasing the ISO. And we know now that that’s going to affect the quality of our image.
There is still, however, a scenario that we haven’t talked about. And that’s if, after all the decisions are made regarding aperture and shutter speed, we’re still letting too much light in, then there’s nothing that the camera can really do about that.
Take this waterfall on the left hand side, for example. There’s a tiny bit of motion blur where the shutter speed is slow enough to capture a small amount of movement in the water. The rocks in the foreground are already getting a bit bright, so if I slowed that exposure down any more to get my water to appear smoother, I’d let far too much light in and my photograph will be overexposed. There are tools called neutral density filters which you screw onto the lens or place in front of them and it’s a translucent material that will block out a certain amount of light, allowing me to use longer exposures that I would normally be able to during the day.
The other example provided is taking photographs of the sun during a partial solar eclipse, which you should never do without any kind of protective equipment as it will not only damage your camera but could seriously damage your eyesight too. For this, I used a very strong neutral density filter which meant that I could take photographs of this crazy bright light source without creating an extreme pure white image like I showed you at the start of this lesson.
I really hope that you’ve enjoyed this lesson and that you’ve found it useful. There’s a lot of information in there so it might be worth coming back again to consolidate what you’ve learned.
I love this quote that says we don’t take photograph, we make it, and that’s what I’m going to help you to do. So, please, if you’ve enjoyed this, make sure you come back for more. If you’d like to receive these articles straight to your inbox, subscribe here: