A camera lens with a focal length of 50mm and aperture of f/1.4 is used to image a scene. The photographer focuses the camera at an object in the scene 4m from the camera. The resolution of the camera at the image plane is such that image points appear out of focus when circles of confusion exceed 0.02mm diameter. Determine the limits of the depth of field in the photograph, i.e. calculate the range of object distances which appear in focus?