Base ISO refers to the ISO sensitivity providing maximum latitude from the image sensor. At this ISO sensitivity, gain is not added needlessly to output signals from the sensor. This level of ISO sensitivity provides maximum performance from a camera's image sensor.

For example, when an image sensor with a latitude of up to 15 stops produces a 15-stop signal at the base ISO, increasing the gain or ISO sensitivity would prevent highlight information from being recorded, because it would not fit within this latitude.

Shooting at the base ISO is required in log shooting in order to obtain maximum latitude.

Models with multiple base ISOs enable you to switch the base ISO to suit the shooting conditions.