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Overview

ISO is one of the three pillars of photography (the other two being shutter speed and aperture) that has a huge impact on the outcome of a photograph. It is a critical setting that determines the amount of light that is captured in a photograph. The higher the ISO value the more light is captured in a photograph. However, raising the ISO value results in grainier photographs, so ISO should only be raised when it is not possible to increase the brightness via aperture or shutter speed settings.

TL;DR

  • ISO represents the photosensitivity of an image. Lower values will capture less light than higher values, but higher values will produce grainier images.
  • The base ISO with produce the highest quality images. For that reason always try to take photographs at the base ISO.
  • Images taken with the base ISO have the least grain and the most dynamic range, providing the most flexibility in post processing.
  • It is not always possible to take images with the base ISO. When taking photographs of subjects with a lot of motion or in very dark environments it may make sense to increase the ISO value to allow for faster shutter speeds or appropriate aperture settings.

What is ISO?

ISO stands for “International Organization for Standardization”, though the term ISO no longer not directly refers to the organization that originally defined it. ISO originally defined the photosensitivity of film, but has since been adopted by digital camera manufacturers.

Common Values

Each camera has a range of ISO values (also called ISO speeds) that is supports, which most commonly increases at a 2x scale. A common set of ISO values is:

  • ISO 100 (low ISO)
  • ISO 200
  • ISO 400
  • ISO 800
  • ISO 1600
  • ISO 3200
  • ISO 6400 (high ISO)

Simply put, when the ISO speed is doubled, the brightness of an image is also doubled.

Base ISO

The lowest supported ISO value on a camera is commonly referred to as the "base ISO" and is an important setting on the camera since photographs taken at the base ISO will create the highest quality images. Ideally all photographs should be taken at the base ISO, though this may not be possible in low light environments.

What ISO Value to Use

Cameras support such a wide range of ISO values since different ISO values are warranted in different situations. When there is ample light though it is best to stick to the base ISO since this will produce the highest quality images. Even in darker environments the base ISO can be used if the camera is stable and a lower aperture and longer shutter speed can be utilized.

High ISO Values

When taking photographs of subjects with a lot of motion it may be necessary to increase the ISO value to appropriately brighten an image while also shortening the shutter speed to avoid motion blur. Essentially, the ISO value can be increased when there is not enough light to capture a bright, crisp image any other way.

Auto ISO

Many cameras have an "Auto ISO" setting in which the photographer can set the maximum ISO. In this mode the camera will select the appropriate ISO value without exceeding the maximum ISO.

Resources