AF illuminator is a feature on many cameras that projects an infrared or bright light beam onto the subject to help the autofocus system determine distance, particularly in low-light conditions. By providing additional illumination, the AF illuminator improves focus accuracy when ambient light is insufficient for the camera's sensors. However, it can be misled if the subject is behind glass or reflective surfaces, as the beam may register the glass instead of the intended subject. AF illuminators are commonly used in portrait, indoor, and low-light photography to achieve sharper images and reliable autofocus performance.