A time-of-flight or electrostatic trap mass analyzer is disclosed comprising: an ion flight region comprising a plurality of ion-optical elements (30-35) for guiding ions through the flight region in a deflection (x-y) plane. The ion-optical elements are arranged so as to define a plurality of identical ion-optical cells, wherein the ion-optical elements in each ion-optical cell are arranged and configured so as to generate electric fields for either focusing ions travelling in parallel at an ion entrance location of the cell to a point at an ion exit location of the cell, or for focusing ions diverging from a point at the ion entrance location to travel parallel at the ion exit location. Each ion-optical cell comprises a plurality of electrostatic sectors having different deflection radii for bending the flight path of the ions in the deflection (x-y) plane. The ion-optical elements in each cell are configured to generate electric fields that either (i) have mirror symmetry in the deflection plane about a line in the deflection plane that is perpendicular to a mean ion path through the cell at a point half way along the mean ion path through the cell, or (ii) have point symmetry in the deflection plane about a point in the deflection plane that is half way along the mean ion path through the cell. The ion-optical elements are arranged and configured such that, in the frame of reference of the ions, the ions are guided through the deflection plane in the ion-optical cells along mean flight paths that are of the same shape and length in each ion-optical cell.