(CLICK FOR FULL-RES)
Now adjust the size and shape of the sharp zone. Click and drag anywhere on the outer circle to enlarge and shrink the area. Drag one of the two small dots to go elliptical and rotate the orientation of the ellipse. Pull out on the square to square off the corners. The four interior dots indicate the beginning of the transition between sharpness and blur. You can pull them inward for a slower transition, which can be a good idea if you chose a high amount of blur.