. "Focal Length" . "out of focus" . "thin lens equation" . . "limiting the focal range of the lens" . "f=" . "focal length" . . "Focal_length" . . "length" . . . . . "Focal length" . . "focal" . "Effective Focal Length" . "focus" . "Focal length" . "f" . "back focal length" . "depth of focus" . "focal-length" . . "focal range" . "Focal Length (of a lens)" . . "focal lengths" . "focus distances" . . "focal length" . "focal length ratio" . "mm" .