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What is the Exposure Triangle?

Exposure Triangle refers to the relationship between ISO, shutter speed, and aperture and how they interact with each other; a change to one setting requires changes to the others. The exposure triangle is one of the most crucial elements in photography and should be one of the first basics of photography beginners learn.   To some degree, perfect exposure is a matter of personal preference, so I will only cover the basics for understanding exposure and how to manipulate Aperture, Shutter Speed, and ISO to achieve your vision. 

Exposure Definition

Exposure is the amount of light that reaches the camera’s sensor and sets the mood for the photo; a high exposure creates a “light and airy” feel while low exposure creates a “dark and moody” feel. 

What Are The Three Components Of The Exposure Triangle?

Exposure Triangle Image

Aperture Meaning

Aperture is the size of the opening in the lens that controls how much light enters through the lens. The wider the opening, the more light that reaches the sensor. This element also controls the depth of the field, also known as background blur.

Shutter Speed Meaning

Shutter Speed is the amount of time the shutter is open, is measured in seconds, and is the easiest of the exposure elements to understand. Longer shutter speeds allow more light to hit the camera sensor.

ISO Photography Meaning

ISO is the camera’s sensitivity to light; a high ISO value makes the camera more sensitive to light and needs less light for the correct exposure.

How The Exposure Triangle Works

If your photos need more light, you can adjust any combination of the three components to  increase the amount of light that enters the camera.

  • – Open your aperture. As I went over in Aperture Made Simple, this means reducing your f stop number
  • – Use slower shutter speed
  • – Increase ISO to increase the camera’s sensitivity to light

The opposite is true if you want less exposure:

  • – Smaller aperture
  • – Use faster shutter speed
  • – Decrease ISO
Exposure Triangle Chart demonstrates how lower f-stop numbers have a wider aperture and allow more light to reach the camera's sensor

How To Adjust The Exposure Triangle

Sometimes you can’t or don’t want to adjust one of the three functions of exposure. If an image is underexposed and you don’t want to use a slower shutter speed, then open the aperture and/or increase the ISO for more exposure. If the image is overexposed and you want less exposure, then use a narrower aperture or decrease the ISO.

Moonrise Illuminates The Stars In The Sky
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.

Use Auto and Priority Modes

Each element impacts more than just exposure so you will need to find the right balancing act for each image. Changing the aperture changes the amount of background blur in an image, shutter speed controls motions, and ISO impacts image noise. That’s a lot to think about in the field, which is why most photographers shoot in aperture or shutter priority mode and use Auto ISO. Aperture and Shutter priority modes allow you to control one elements while the camera adjusts the other settings for you. Evaluate the scene and choose priority mode that is most important for creating the look you want. 

Shutter Priority Mode allows you to control shutter speed and is best for wildlife, waterfalls, sports, and low light photography.

Aperture Priority mode allows you to control the aperture and is best for macro photography, portraits, and landscape photography.

Auto ISO can be used at any time, even in manual mode. The secret to auto ISO is to adjust the maximum ISO settings in the camera so the camera will never exceed an ISO mode you are comfortable with. This will require thinking more about aperture and shutter speed, but you will avoid excessively noisy images and you can override the max ISO for a single image by manually adjusting the ISO.

Examples of Using The Exposure Triangle

Camping In Big Bend

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.

Gold Butte Lookout Tower in Detroit Oregon

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 amount of time the shutter is open. Given this is an old building, I didn’t mind the extra digital noise.

There is no hard and fast rule on how to choose the exposure settings for a particular scene. If you don’t like an image’s exposure, look at the 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 Your Knowledge

The photo below is overexposed, what could you change to get a better exposure?

Camera Settings:

ISO: 100

Shutter Speed: 1/125

Aperture: f/5.6

Overexposed Example shows harsh highlights and ruins the image


Answer: Use a faster shutter speed.

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



Exposure Triangle Pin