If you have been following along over the past few weeks, then you will already understand how the individual exposure settings (ISO, aperture, and shutter speed) work. With these three settings there are an uncountable number of combinations that can be used to create an image. It can seem like a lot to take on, but with a little bit of direction you can learn how to control every aspect of your photograph. Before we cover how though, we'll do a brief refresher on some of the basics.
Basics Of Exposure
In photography, the term "stops" is used in a number of situations. Basically it's a measurement of the difference in the amount of light between two exposure settings. Full stops are a geometric sequence based on multiples of 2. This means that adding one stop will double the amount of light, adding two stops will quadruple it, and adding three will be eight times as much light. Conversely, subtracting a stop will halve the amount of light, minus two stops will be a quarter of the light, and so on.
Exposure value, or EV, is the measurement of how bright an image is, and is closely tied to stops. An EV of 0 means the total image is averaged out to middle gray. You can learn more about how this is determined in my post on metering
As you move up and down the EV Scale you are in effect measuring the stops between images. +1 EV is a reflection of the image being 1 stop brighter compared to 0 EV, and -1 shows the image is one stop darker.
A measurement of how sensitive to light your cameras sensor is. Learn more here.
Rated in f/stops, Aperture controls how much light is able to enter your camera. Also controls depth of field. Learn more here.
The amount of time that your sensor is exposed to the available light. Controls motion blur. Learn more here.
Building Your Exposure (Pyramid)
Contrary to many photography teachers out there, I like to think of the exposure settings working like a pyramid. Each setting relies on the others to build an image, just like a pyramid only works with every layer in place. As I have been covering it, the exposure pyramid looks like this:
This layout isn't an arbitrary one, I set it up this way specifically for teaching purposes. I use ISO as the first layer because it sets how sensitive the camera's sensor is. This setting creates a foundation for us to build your exposure on, just like the bottom layer of a pyramid.
Aperture is second because it controls how much light is available to hit the sensor. Creating an exposure is all about controlling light, so this is a natural second level.
Finally, the last level is shutter speed. Now that we have the sensitivity to light, and the amount of light established, we set how long the light is able to hit the sensor.
All together, these three combine to create your exposure. Changing any individual settings will impact the brightness of your image. This is why it's important to understand how the three work together; when you want to adjust your photographs EV, you'll know exactly what to change to accomplish this. The above process is how I typically create my exposures, but of course this isn't the only way to do it.
Switching things up
Once you understand how the three exposure settings work together to build an exposure, you can start to shake things up a bit. In reality the exposure pyramid doesn't have to look the way I have set it up. Any of the three settings can be placed at any level of the pyramid; it just depends on what is most important to your image.
Each setting has additional effects beyond simply controlling the light. Higher ISOs can add noise to your photograph and lower image quality, Aperture changes how much of the image is in focus, and shutter speed controls how much blur there is due to movement.
If you care most about image quality, then you will want to set a low ISO as your first setting. If it's a particular depth of field, then aperture will come first. And if your are concerned with camera shake, or you want to freeze action, then shutter speed is the setting you should base your exposure on.
From this foundation you then pick the second most important setting, and then balance everything out with the final setting. Below are a handful of the possible combinations.
More Than One Way
Now that you know how many approaches to building an exposure there are, I'll throw on one final bit of knowledge: you can make the exact same exposure (EV) using completely different setting combinations.
When you change one setting, you can compensate for it with the other settings. This works because exposure is like an equation with each setting as a variable. This equation would look something like:
Exposure value = ISO + Aperture + Shutter speed
If you look at it this way then you can easily see that there are many ways to create the same answer, just like there are many combinations of number that add up to 12.
12 = 2 + 5 + 5
12 = 1 + 5 + 6
12 = 4 + 4 + 4
12 = 2 + 2 + 8
12 = 7 + 3 + 2
If you change one setting, say aperture, by +2 stops, then you can change another setting -2 stops to create the same exposure, OR you could change both ISO and shutter speed by -1 stop. Either way you would still have the same EV. This works with any setting, and any amount of stops, as long as you correct with the the other settings. Below you can see some examples of this in action.
The Last Word
Exposure is all about finding a balance between all three settings. The final combination will always be different based on the light available and your vision for the photograph. Understanding how to control that light, and knowing what to change to achieve your desired results is half the battle.
There has been a lot of information in this post, so if you have any questions please ask it in the comments and I will answer it to the extent of my knowledge. The best way to understand all of this though, is to go out and practice it. Go out and make an exposure, then fiddle with the various settings to experience how they change your image.
While you may not always use this ability to control the whole image, having the knowledge of how to craft your perfect exposure will only make your photography better.