What is Exposure?

Every time you press the shutter button on your camera to make a picture an exposure is taking place. Exposure is the amount of light that is passes through your camera’s lens and is recorded by either a sensor (in digital cameras) or the film.

What Controls Exposure?

Regardless of what settings you’ve selected or the type of camera you are using, exposure is controlled by three different elements: Aperture, Shutter Speed & ISOThese three elements all effect the exposure but also effect the appearance of the photo as well. This can allow a photographer to make a ‘correct’ exposure in a number of different ways, each with a different look and feel. The interaction between aperture, shutter speed and ISO and how they effect exposure is often refereed to as and illustrated as the Exposure Triangle.

Exsposure Triangle

How do Aperture, Shutter Speed and ISO Effect Exposure?

Aperture, shutter speed and ISO all have the power to effect the overall exposure of an image and can be controlled to varying degrees, depending on the settings or mode a photographer chooses. However, as I previously mentioned they also have the power to effect the appearance of the image beyond exposure.  Let’s examine these effects briefly (if you’d like more details simply click the appropriate links)


As the name suggest, aperture refers to hole in the lens and how much it opens up to allow light in. The larger it opens the more light is allowed in, resulting in a faster or slow exposure.

Aperture can also help to control depth of field (DOF) or how quickly the in focus area of an image is allowed to go blurry. In different situations, this can allow a photographer to keep everything in focus or create a background that visually appears to be one big blur.

Shutter Speed

Shutter speed effects the duration of the exposure. Faster shutter speeds have the potential to freeze action, while slower shutter speeds can allow the movements subject or camera to blur the image.


Also commonly known as film speed, ISO refers to how sensitive the film or digital sensor is when light hits it. The more sensitive it is the quicker it exposes.  The large the ISO number the faster film or sensor sensitivity. Slower ISO have the advantage of creating the often more preferable, cleaner image, while larger/faster ISOs produce more noise or grain.

Looking for more information?

Check out this video by Mark Wallace and the good folks over at Adorama. The video goes into far more depth than this post so it may be worth reading the posts on aperture, shutter speed and ISO before you watch.

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