The present disclosure relates to an electron-optical stack for manipulating one or more charged particle beams and associated apparatus and methods. In one arrangement, a plurality of electron-optical plates have major surfaces on opposite sides of the plates. The plates define a set of channels configured to be aligned along a beam path of a charged particle beam to allow the charged particle beam to pass through the plates via the channels. Each channel defines apertures in the two major surfaces of the plate that defines the channel. The apertures have different shapes from each other in the sense that one aperture has a nominal shape and the other aperture has a perturbed shape, i.e., a perturbed version of the nominal shape. The plates are oriented such that the apertures comprise one or more matching aperture pairs along the beam path. The or each matching aperture pair consists of apertures having the same shape defined in adjacent major surfaces of adjacent plates, i.e., they have both either a nominal shape or a perturbed shape.