The Exposure Triangle.
in it’s most basic form photography is about light and shade. So understanding how your settings affect how your camera sees light will give you control over how the image looks.
When you start out the relationship between the three exposure settings seems complicated but it’s really not and by the end of this it will all make perfect sense, especially as your camera will help you.
The Exposure Triangle.
More light = brighter picture, easy.
Each of these three will increase or reduce the exposure and each in a different way. We won’t go into too much detail about the effects of each here but we tackle each in turn.
First Principle – Stops.
Exposure is measured in stops. To change your exposure by one stop means to either double or half the amount of light that the sensor gets. Here’s the good news, the three elements of exposure are all measured in stops too. This means that it becomes easy to adjust one and then know how you need to adjust the others to suit.
Let us start with the most obvious, how long light is hitting the sensor. If your shutter speed is 1/500 then the shutter is getting light for 1 500th of a second. If we want to increase the exposure by one stop we need to give the sensor light for twice as long. So we change our shutter speed to 1/250, this way light is hitting the sensor for 1 250th of a second.
Of course, if we want to reduce the exposure by one stop we need to reduce the time the sensor gets light by half. 1/500 becomes 1/1000, now the sensor only has light on it for 1 1,000th of a second.
All good so far?
This controls how sensitive the sensor of the camera is. In the good old days of film, this was set by the film you put in the back of the camera. If you wanted a different film sensitivity you had to put a different film into the camera.
Also, you were generally limited to a choice of 100, 200 or 400. There were other specialist films available but for the average Jo that was your choice.
In the case of ISO bigger number means the sensor is more sensitive to light. So ISO 800 is one stop more than ISO 400.
So let’s start with our camera set to 400 ISO. If we want to increase the exposure by one stop we double the sensitivity of the sensor so we go to ISO 800.
And of course, if we want our ISO 400 reduced by one stop we half the sensitivity of the sensor (half the ISO) so we select ISO 200. See what I mean, this stuff is simple.
Aperture / f-stop.
Just as you’re getting comfortable I’m going to throw you a slight curveball, but it’s only a small one. The aperture figure is a calculation between the focal length and the diameter of the lens. This means when you double or half the number you actually move by 2 stops. So f4 to f8 is a two-stop difference.
Don’t let that worry you too much at this point, you’ll get used to it very quickly. Unlike the ISO, a smaller number means more light when it comes to aperture.
So let’s start at that aperture at f4. To double the amount of light coming through the lens we open it out to f2.8, this will give you an extra one stop of light.
To take our f4 down a stop and half the light coming through the lens we close the aperture down to f5.6
How to change but stay the same.
Ok, so let’s look at how we take an expose, change it around and keep it the same………….
So what have we got so far? From the example above our exposure is:
1/500th – ISO400 – f4
Let’s take one stop out of the shutter speed, we go from 1/500 to 1/1000. The shutter is open for half the time so only half the light is hitting the sensor.
We’ll start there with the sensor, we can make it twice as sensitive and change it from ISO400 to ISO800.
1/1000 – ISO800 – f4 and we have the same exposure.
Aperture next, we have decided we don’t want to change the ISO so we will add a stop with the aperture, easy, change or f4 to f2.8.
1/1000 – ISO400 – f2.8 and once again we have the same exposure, Three ways to get the same exposure.
Just for good measure let’s do a little of both. We’ll take two stops out of the shutter speed and add a stop in ISO and a stop in the aperture.
Putting them all together –
Just to get a little more extreme let’s take the shutter speed up to 1/4000. We started at 1/500 so here we go -> 1/1000 (1 stop) -> 1/2000 (2 stops) -> 1/4000 (3 stops). We need to find 3 stops.
ISO 400 -> 800(1 stop) -> 1600 (2 stops) -> 3200 (3 stops).
Aperture f4 -> f2.8 (1 stop) -> f2 (2 stops) -> f1.4 (3 stops).
A mix 1/4000 – ISO800 (1 stop) – f2 (2 stops) and we are back to our original exposure.
I’m deliberately not saying the same result so we’ll touch on that a little. There will be a link to articles that go in more depth but let’s have a quick look at why you might want one of these values in a certain range.
Shutter speeds role in the exposure triangle is about how well you can freeze action. If you have a fast-moving object and you want it sharp you might want to use the fastest available shutter speed at set it to 1/8000.
Maybe the opposite is true and you want to add some movement or motion blur into your image. So maybe you want a shutter speed in the 1/100 range.
As a rule of thumb the lower your ISO the cleaner the image you will get. With modern cameras and the correct exposure, you’d have look really close to notice anything below about ISO3200.
This is more of a creative choice. If you want a shallow depth of field you may want to set you aperture at around f2. Or maybe you are taking a vast landscape and want as much in focus as possible so you want to use f22.
Your camera will help you.
As I say in the beginning, your camera will help you too. Every modern camera that has manual control also has an exposure meter. In most cases, as you look through the viewfinder or even on the LCD screen you will see the meter.
Depending on how you have set the metering it will measure the scene and tell you if you how you if your exposer is on, under or over.
Again to make this really easy to understand the information is measured in stops. You’d think that somebody had actually taken time to think this through and make it easy for you.
When you are taking pictures in an automatic mode the camera will adjust the settings to put the exposure at 0. When you are shooting in manual the marker will move to tell you if you are under, over of spot on. – figures (to the left) tell you that you are underexposing. + figures (to the right) tell you you are overexposing and it even tells you by how many stops.
That way you can quickly adjust whatever setting you feel most appropriate to get your desired shot.
So….. Why learn this?
If the camera takes care of all this on any auto mode why should you bother to learn how it works. You want pictures with a shallow depth of field, pick up the 50mm f1.8 here (and yes I will continue to push this lens as it’s fantastic value and a game-changer). Stick your camera on Aperture Priority and let the camera figure the rest out, right?
Well, yes and 90% of the time that will get you a balanced exposure. It may not get you the exposure you want and here’s why.
First – Even if you never shoot in manual you should at least understand how exposure and what the camera is doing.
Second – Depending on how you have your metering set up your camera may meter based on a different something different than your subject.
For example, You take a picture of your partner and there is a lot of light behind them. Your camera may take that light into account and you end up with your partner being a silhouette.
Third – You are taking pictures in a dark environment, your camera is likely to drop the shutter speed to compensate and this results in very blurry pictures.
Every environment is different, every photographer has a different goal for their finished images and although cameras are getting smarter all the time at this stage they can’t read your mind and know what you want the image to look like.
If you want to learn more about aperture and depth of field take a look at this article here>>
That’s a quick look at the exposure triangle and hopefully, it’s all a little bit clearer now. If you want to know more I recommend this book to get into the details of exposure a little more.