Circle of confusion

The circle of confusion refers to the optical phenomenon in photography where a point of light is not rendered as a sharp point on the image plane but instead as a small, blurred circle. This occurs due to factors like lens imperfections, defocus, and the limited ability of lenses to focus all points of light perfectly. In depth of field discussions, the circle of confusion is crucial, as it sets the threshold for what is considered an acceptably sharp image point. It plays a significant role in determining the perceived sharpness or blur in different parts of a photograph, especially in areas outside the plane of focus.