An electrostatic lens, operated in accel-decel mode, is presented. The lens has advantage of low chromatic aberration, which is about 2/3 the amount produced by a conventional einzel lens operated in decel mode. The lens has two pieces of electrodes built in to accelerate and decelerate the beam. The decelerating electrode works as a main lens, while the accelerating electrode enhances the beam energy, reducing the aberration. Calculations for the accel-decel lens provide C-c of 22 mm and f of IP mm with working distance of 5 mm. The lens is suitable for producing a fine beam with a smaller spot size and With energy of over a few tens of kiloelectron volts. When the lens is applied to a 30 keV focused ion beam with 1 pA current, the spot size is estimated as 4.8 nm in diameter on a target with the above working distance.