What is the exposure triangle?

Switching the camera mode dial from auto to any non-auto mode is a nice start, but to truly be a proficient photographer who must truly understand the exposure triangle, is tough. The exposure triangle is simply the relationship between your ISO, shutter speed and aperture. These three components work together to create an actual exposure or photograph.  It is referred to as the exposure triangle because when you adjust one element, another element MUST change to capture the same exposure.  When learning the photography basics and understanding the exposure triangle it is paramount to always remember this cause and effect relationship.

Before we get into the details and specific technical examples about understanding the exposure triangle, let’s first make sure we understand each of the elements – ISO, shutter speed and aperture.

What is ISO?

  • ISO or ASA is a term from the film photography days which referred to film sensitivity to light.
  • The lower the film sensitivity or ISO the less “grainy” the photo will be. The same concept is true today with digital photography, as ISO now refers to the sensitivity of the camera sensor.
  • Just remember, the lower the ISO number, the cleaner looking your photo will be. This means there will be less “grain/noise.”   However, keep in mind that sometimes photographers use high grain/noise as an artistic effect.
  • For a far more detailed discussion on ISO, check out this post: ISO Explained the Easy Way!

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exposure triangle

What is Shutter Speed?

  • Shutter speed is simply the amount of time (measured in seconds) that the camera’s shutter is open allowing light to hit the sensor to make an exposure. The higher the number, the fast the shutter will open and close.
  • Example Shutter Speeds: 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2 etc…


  • Aperture refers to how large or small the opening is thru the lens, as you can see in the above illustration.
  • This opening is what controls how much or little light can pass through the lens and onto the camera’s sensor.
  • Each lens has its own aperture range. This means one lens can open as wide as f/1.4, while others start at f/4.0. Aperture is measured in “f-stops” and a lower f-stop number such as 1.8 means a wider aperture (lets in more light), a high “f-stop” number like f22, means a narrower aperture, letting in much less light.
  • Aperture/f-stop numbers: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32
  • Want to learn more about aperture?  Read this post: Fundamentals of Photography – Understanding Aperture

exposure triangle

Putting ISO, Shutter Speed and Aperture Together

The easiest way to think of how all three work together to give an exposure is to keep one of the three components constant. Let’s make ISO the constant (so don’t worry about that changing). The next step is to choose your f-stop or aperture.

Remember that both aperture and shutter speed both control how much light is coming in thru the lens (aperture) and onto the camera’s sensor (shutter speed). Therefore, if using a wider aperture (lower f-stop number) you are letting in more light and therefore your shutter speed should be faster compared to when using a narrower aperture (higher f-stop number) for the same given exposure.

An example for you:

Based on the light outdoors, you set your ISO at 200. If you’re taking a photo and you’re using aperture priority mode, you set the camera lens to f/4, and the camera selects 1/250th as the appropriate shutter speed. If you decide to change the aperture to f/2.8 you are now letting in more light into the camera requiring an adjustment on shutter speed (faster) to let in the same amount of light between aperture and shutter speed. Since you are keeping ISO constant, the new shutter speed with an aperture at f/2.8 from f/4 would be around 1/500th of a second.

Changing the aperture from f/4 to f/2.8 is letting in twice as much light, so in order to compensate for that extra light, the camera is choosing a twice as fast shutter speed – 1/250th to 1/500th. Don’t worry though, in aperture priority mode, you just change the aperture and the camera’s light meter will determine the correct shutter speed.  To see why I love shooting in aperture priority mode over manual sometimes check out this read.

Understanding the Exposure Triangle

Always remember to think of “exposure” as simply the amount of light hitting the camera’s sensor or film. The sensor/film is being “exposed” to the light. We can control how much light hits the sensor by:

  1. Aperture – How LARGE of lens OPENING
  2. Shutter Speed – How LONG of a time the shutter remains open, to allow light in.
  3. ISO – How SENSITIVE to light the actual sensor is

Key tips to help you:

  • Always use the lowest ISO as possible! That way, you can try to achieve the cleanest (less grainy) images with the best dynamic range and color depth. Outdoor, this will range from ISO 100-400, Indoors ~ISO400-3200, Dark Receptions ISO 1600+. Please note that these values will vary slightly depending on the ambient light in the situation.
  • For faster shutter speeds (to capture movement), use wider apertures and/or higher ISO.
  • To prevent motion blur and get sharp photos, shutter speed should be at minimum 1 / (double your lens focal length) for full frame sensor cameras and 1/(1.5 x focal length) for crop sensor cameras. Note: rule above is rule of thumb for stationary subjects, moving subjects may require faster shutter speeds.

If you are a visual learner make sure to check out this video! This will help improve your understanding of the exposure triangle! Please let me know in the comments if there is anything I can explain further, or doesn’t make sense! I’m here to help you!

Now it’s your turn!

I’d love to hear from you! What exposure element do you struggle with the most? Understanding ISO, shutter speed or aperture? What mode do you prefer? Hit me with all your questions!

Catch ya later,

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