Electromagnetic lens p.87 on textbook Electron Source of Soft Fe pole beam electrons pieces. Bore 极靴 Axis Electron trajectory 068086-/.… Focal point Copper windings Cu coils Iron shroud- Gap Magnetic Focus lens field Focal length is determined by field strength: V K:constant based on coil f=K V:accelerating voltage i:mA of current 13Electromagnetic lens 13 Focal length is determined by field strength: K: constant based on coil V: accelerating voltage i: mA of current 极靴 Bore Gap p.87 on textbook