What’s the Catch With High ISO? The Catch ISO 100 dark, but clean ISO 1600 bright, but grainy Crank up a quiet radio station and you hear the song, and the static too. High ISO works the same way: the picture gets brighter, and so does the noise. ISO 100: dark, but clean. ISO 1600: bright, but grainy. Nothing is free. Previous lesson:← What Does ISO Do?↑ Back toUnderstanding ExposureNext lesson:Exposure Wrap-Up: What Did You Just Learn? →