1302886 Electron beam deflecting systems SIEMENS AG 4 March 1970 [5 March 1969] 10265/70 Heading H1D A corpuscular beam apparatus using two pairs of deflection elements at a common axial location, is provided with two pairs of stigmator elements disposed at 45 degrees to the deflection elements. In Fig. 2 the deflection coils 10-13 are wound on a former 14 of synthetic material or of aluminium. Two sets of stigmator coils 15-18 and 15<SP>1</SP>-18<SP>1</SP> are preferably wound separately before their assembly, although a common former can be used, and the entire arrangement can be potted. If the deflection coils are energized by a current u, stigmatism can be reduced by energising the stigmator coils proportional to u; alternatively it can be eliminated by supplying the coils with a current proportional to u<SP>2</SP>. When two sets of deflection coils are located at displaced axial positions, both may include stigmator coils, but preferably only the one nearest the beam source is provided with stigmator coils. In the latter case the two sets of coils may be energized in series with a current u and with a current proportional to u<SP>2</SP> or u<SP>3</SP>, whereas the stigmator coil is energized with a current proportional to u<SP>2</SP> (Fig. 4, not shown). This allows both stigmatism and distortion to be compensated, the latter being the undesired displacement of the beam from the axis as a result of two equal and opposite deflections. The deflection and/or the stigmator elements may be electrostatic instead of magnetic.