Abstract: An electron image projector for projecting mask patterns with unity magnification onto a semiconductor slice comprises a cathode from which emitted electrons are accelerated by a uniform electric field and focussed by a uniform magnetic field onto a target. To reduce the dependency of electron trajectories on the local shape and disposition of the target, the uniform electric field is applied by an accelerating voltage between the cathode and a grid electrode acting as the anode between the cathode and target. The grid is positioned at a first magnetic focus, and the target is positioned at a second magnetic focus of the uniform magnetic field. A small voltage much less than the accelerating voltage may be applied between the grid and the target to obtain correct focussing. Structure is also provided to move the grid parallel to the target during exposure in order to prevent the grid pattern from being reproduced on the target.