Let me try to explain this here...
Theoretically, when a lens focuses on a scene, there will only be a single plane where the image is in focused. Moving away from the plane of focus, the image will get increasingly blur.
Our eyes have limited resolution. In a photo, although the image is blurred immediately away from the plane of focus, our eyes do not detect it and still perceive it to be still in focused. This total distance in front and behind the plane of focus where the eyes still perceive as sharp is known as the depth of field. The circle of confusion is defined as how much a point needs to be blurred before the eye perceives it to be out of focus.
Theoretically, when a lens focuses on a scene, there will only be a single plane where the image is in focused. Moving away from the plane of focus, the image will get increasingly blur.
Our eyes have limited resolution. In a photo, although the image is blurred immediately away from the plane of focus, our eyes do not detect it and still perceive it to be still in focused. This total distance in front and behind the plane of focus where the eyes still perceive as sharp is known as the depth of field. The circle of confusion is defined as how much a point needs to be blurred before the eye perceives it to be out of focus.