Working distance

Working distance A is the distance between the entrance aperture's central axis and the working plane. A is determined by the focal length and mounting position of the F-Theta objective (if present). For prefocus systems, working distance A is determined by the dynamic focusing unit in the null position ("z=0" plane).

Free working distance A' is the mechanical distance between the scan system (bottom edge of housing including objective) and the "z=0" working plane.