Depth of field preview is a camera feature, usually activated via a button or lever, that allows photographers to stop the lens down to the selected aperture before taking a picture. This lets you see exactly which parts of the scene will be in focus at the chosen aperture. While the viewfinder will appear darker, this tool is invaluable for judging sharpness, controlling composition, and ensuring that important elements of the scene are acceptably sharp. Depth of field preview is especially useful in macro, landscape, and studio photography, where precise focus across the subject is critical.