defocused

Defocused is an adjective used to describe an image or optical system in which light from a scene point does not converge to a sharp point on the image plane; instead, it forms a blur circle. The degree of blur depends on aperture, focal length, subject distance, and the focusing position relative to the subject. When the plane of focus is correctly matched to the subject, the image is in focus; otherwise it is defocused.

Causes and forms: Common causes include incorrect focusing distance (the subject is not at the lens’s focus distance), camera or lens misalignment, or movement during exposure. A wide aperture or long focal length increases apparent defocus by reducing depth of field, so areas outside the focus plane become blurred. Defocus can affect the entire image or be used selectively to create background or foreground blur known as bokeh.

Correction and use: The amount of defocus is described by the circle of confusion; a smaller circle yields a crisper image. Correct by refocusing, using autofocus, or focusing manually with live view magnification. Lens calibration and proper focusing technique help avoid unintentional defocus. Defocus can also be used intentionally in art and photography to soften detail or to create characteristic blur patterns. In some contexts, defocus techniques are employed in astronomy and cinema to manage brightness, depth, or artistic effect.