The Basics of the Exposure Triangle

Exposure Triangle Cover Photo

Each element of the exposure triangle impacts the others; changes to one will require changes to the others. Exposure is the amount of light allowed to reach the sensor and sets the mood for the photo. High exposure creates a “light and airy” feel while low exposure creates a “dark and moody” feel. Since “proper” exposure can vary depending on personal preference, I won’t dive too deep into exposure itself. Just understand that overexposed means there is too much light and underexposed means there is not enough light. Instead, I will explain how to achieve your vision by understanding how ISOShutter Speed, and Aperture work together.

Exposure Triangle

If your photos need more light you can manipulate the exposure in one or more of the following ways:

  • – Open your aperture. As I went over in Aperture Made Simple, this means reducing your f stop number
  • – Decrease shutter speed, as in a slower shutter speed
  • – Increase ISO

The opposite is true if you want less exposure:

  • – Narrower aperture
  • – Increase shutter speed, as in a faster shutter speed
  • – Decrease ISO

When you’ve decided on a shutter speed but the image is underexposed, then you can open the aperture and/or increase the ISO for more exposure. If the image is overexposed and you want less exposure, then use a narrow aperture or decrease the ISO.

Moonrise

If you’re set on your aperture instead, you could decrease your shutter speed and/or increase your ISO to get more exposure. Or increase shutter speed and decrease ISO for less exposure.

Since ISO only changes the amount of noise in a photo, it’s best to set aperture and shutter speed first and then determine an appropriate ISO. If aperture and shutter speed are a priority, then your only option for more exposure is to increase the ISO. You can generally use a pretty high ISO before noise is noticeable, however, if you want a lower ISO, then you would need to decrease shutter speed and/or open the aperture to increase exposure. If you do not wish to change two of the exposure settings, then the third is the only option for changing the exposure

In this photo, I set the aperture to f/22 for sharp landscape lines and the ISO to 100 for minimal noise.  The only option to get adequate exposure with these settings was to increase the shutter speed to 30 seconds. 

Conversely, I used a  very fast shutter speed, 1/4000, and a fairly low f-stop, f/4, in this photo.  To get enough exposure, I needed to increase my ISO 12800.  If 12800 was too much noise, my first thought would have been to decrease the shutter speed. 

There is no hard and fast rule on how to choose the exposure settings for a particular scene. If. you see that an image is over or underexposed, look at your settings to see what you can tweak. If you don’t like the exposure and don’t want to adjust the shutter speed, there are a variety of ways to manipulate ISO and aperture to adjust the exposure.  

Test Yourself

The below photo is overexposed, what could I have changed to get a better exposure?

Camera Settings:

ISO: 100

Shutter Speed: 1/125

Aperture: f/5.6

Answer

Answer: Increase shutter speed, as in use a faster shutter speed.

Explanation: ISO was already as low as it could go and aperture wasn’t that high.  But, shutter speed could have been much faster.


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