What aspect does adjusting the ISO setting on a camera primarily affect?

Adjusting the ISO setting on a camera primarily influences the image brightness and grain. ISO measures the camera sensor's sensitivity to light. A higher ISO setting allows for greater sensitivity, making it possible to capture images in lower light conditions and resulting in brighter photographs. However, increasing the ISO also introduces more noise or grain in the image, which can affect the overall quality.

In bright conditions, a lower ISO setting is typically preferred to avoid excessive brightness and maintain image quality. Therefore, understanding how ISO impacts light sensitivity is crucial for photographers aiming to optimize exposure levels while managing image quality.