The angle subtended at the lens by the diameter of the largest circle within which the lens produces an image with acceptable sharpness and even illumination. It defines the usable portion of the lens's image circle and is important for determining coverage on a given film or sensor format. A larger angular field allows more of the scene to be captured with consistent clarity, while lenses with smaller angular fields may exhibit edge softness or vignetting. Understanding angular field helps photographers choose lenses for landscapes, architecture, and wide-format imaging.