What is ISO?

What is ISO?



Robert Patterson


Canon, 5DII







Focal Length



1200 x 800

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Robert Patterson

What is ISO?

Author: Robert Patterson Difficulty: difficulty-icon 2391 views

The low ISO values ensure the smooth color in this photo. This makes the blurriness in the background and foreground all the more effective. So what exactly is ISO? In short, ISO measures sensitivity to light.

In this tutorial you will learn:

  • A low ISO value means that the sensor is less sensitive to light.
  • Using a lower ISO produces clearer, smoother images.
  • Using a higher ISO can result in grainier, 'noisier' images.
  • Avoid high ISO values except in low light situations, when a long exposure isn’t possible.
  • As a rule of thumb, an ISO of less than 800 will produce clear images.

See a few more examples below.

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Written Tutorial






ISO (International Standards Organization)refers to the sensitivity of the cameras sensor to light. This is an industry wide standardized scale that was originally designed to measure film sensitivity to light but when adapted to digital cameras, takes on the exact same role.

At low values, 100 to 400 ISO, a cameras sensor is less sensitive to light. This means that the sensor will have to be exposed for a longer period of time to capture the correct exposure, than it would at a high value ISO. As with film though, the higher the ISO value the grainier and noisier the image will look so for really sharp clean images you will always want to shoot at the lowest possible ISO setting.

In low light situations, to achieve proper exposure, you will have to use high ISO values to prevent the need to shoot long exposures that will turn out blurry (see camera shake in the Exposure section of this tutorial).


User-added image
Low ISO No noise
User-added image
High ISO Visible noise and grain

So to summarize, always use the lowest possible ISO value for the lighting conditions you are shooting in. Values from 100 to 800 are fairly free from distracting graininess and are improving rapidly with each generation of camera. Anything above 800 will start to show grain and noise but is sometimes necessary if you dont have enough light.

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