Exposure – The Photographic Triangle
Written by: What is the Photographic Triangle?
Exposure = Shutter Speed + Aperture (f/stop) + ISO
So what does all mean? It means that the Shutter Speed, f/stop, and ISO settings are all related to one another. By changing one, you affect the others.
There is a popular analogy that does a good job explaining this. Imagine you have an empty bucket that needs to be filled with water. To fill the bucket, you can pour a small stream of water for a long time, or a large stream of water for a short time. Either way you end up with the same amount of water. So here’s the same formula above written in this new scenario.
Full Bucket (exposure) = Time the Faucet is open (shutter speed) + Size of the pipe (aperture or f/stop) + Size of the Bucket (ISO)
When you fill that bucket to the top you have the correct exposure. Too much water and it’s overexposed, not enough water and it’s underexposed.
Back to Light and Exposure
Lets talk in terms of your camera now. When you want to find the correct exposure you have to look at three things: Shutter Speed, Aperture, and ISO.
ISO
I’m going to start with ISO cause it’s probably the easiest to understand. Your ISO is the sensitivity of the digital sensor or your film. The higher the ISO number, the more sensitive the sensor/film is. ISO’s normally ranges from 100-800 (higher-end cameras can provide a wider range). Under normal, bright shooting conditions you should set your ISO to the lowest number (100 in this case).
In the bucket example think of an ISO of 100 being a 5-gallon bucket and the higher the ISO, the smaller the bucket size. This means it takes less water or a shorter amount of time to fill it.
Aperture or f/stop
Without going in depth, your aperture is the size of the opening light passes through. The larger the opening, the more light can pass, the smaller the opening the less light can pass. The size of your aperture is referred to as your f/stop. A common range would be f/2.8 – f/22 (this range can be higher and lower). The smaller the f/stop number, the wider the opening. For example f/2.8 is a wide opening, and f/22 is a small opening. This often confuses people. I’ll save the technical reason for another time.
So in our water analogy, the aperture is the amount of water that can flow through the pipe. The larger the opening the more water that can pass through. The smaller the opening the less water can go through. A smaller opening means you have to leave the faucet open longer(shutter speed). A larger opening means the faucet is open for a shorter period of time(shutter speed). See how easy this really is?
Shutter Speed
The shutter speed relates to the amount of time the shutter is open. Shutter speeds may range from 8 seconds to 1/1000th of a second (higher-end cameras provide a larger range).
In our water analogy, this is the amount of time the faucet is open. The longer you leave it open the more water gets through, the shorter you leave it open, the less amount of water gets through. Again, this is easy to understand, so lets put it all together again.
It’s all relative
When you’re first learning how to shoot manual, just keep the ISO setting the same. This will make it easier for you to see how changing the shutter speed and aperture will affect the exposure. Once you understand the relationship between them, then start playing with the ISO.
All cameras now come with auto-exposure and this works even when shooting in Manual mode. Just look through the viewfinder and see what the camera tells you. Adjust either your shutter speed or aperture, or both to get the correct exposure.
So that’s it! That’s how you get the correct exposure:
Exposure = Shutter Speed + Aperture (f/stop) + ISO
Now go try it out!
