Design, Photography, & Fashion

Learn About Photography: What Is ISO?

Written by MasterClass

Apr 15, 2019 • 2 min read

There are three camera settings a serious photographer should know: shutter speed, aperture, and ISO. They constitute the “exposure triangle.” ISO refers to light sensitivity, and is perhaps the most nebulous and least understood of the three.

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What Is ISO?

ISO is a camera setting that determines your camera’s sensitivity to light. In terms of image quality, a low ISO value means your image will be darker and have less grain (or noise). A high ISO number means your image will be brighter and have more grain. The letters “ISO” stands for International Organization for Standardization, the group that established the standards for light sensitivity in film. The term stuck and still refers to light sensitivity in digital photography.

What ISO Numbers Mean

Most digital cameras have the following ISO values:

  • ISO 100
  • ISO 200
  • ISO 400
  • ISO 800
  • ISO 1600
  • ISO 3200
  • ISO 6400

Each ISO number represents a doubling of the image sensor’s light sensitivity. For example, a camera set to ISO 200 is twice as sensitive to light as one with an ISO 100 setting.

A low ISO means your camera is less sensitive to light and is better suited to bright situations. A higher ISO means your digital camera becomes more sensitive to light and will take better photos in darker settings.

How to Determine the Best ISO Settings

Here’s an idea of what the ISO numbers mean for particular lighting conditions.

  • ISO 100-200: Best for bright daylight. Results in a crisp image with little grain or noise. Your camera’s default ISO base setting will likely be in this range.
  • ISO 200-400: Slightly less ambient light, such as indoors during the daytime or outdoors in the shade.
  • ISO 400-800: Indoors, with a flash.
  • ISO 800-1600: Low light indoors or at night when you can't use a flash.
  • ISO 1600-3200: Extreme low-light conditions without a flash. Your image will have a lot of grain or digital noise because of the low light.

ISO settings lower than 100 or higher than 6400 are typically reserved for specialized camera uses, such as night photography, freezing extremely fast movement, or using a long lens on a handheld camera.

How to Set ISO on a Digital Camera

Your digital camera may default to an “Auto ISO” setting, which means it automatically adjusts your camera sensor’s light sensitivity to your current conditions. Some cameras default to a relatively low ISO, which is suitable for most casual photography in daytime conditions.

To override the Auto ISO settings, select “manual” on the top dial or on your display.

What Is ISO in Film?

While ISO is easily adjustable on a digital camera, ISO in film photography is predetermined by the film you choose. The ISO ratings are written both on the box and on the film canister. Some film cameras have an ISO knob, which indicates which ISO film you have put into the camera, in case you forget.