An ion generator for the formation of electrostatic images includes two electrodes (a "control electrode" and a "driver electrode") at opposite faces of a solid dielectric member which are electrically actuated to form ions in an air region adjacent the control electrode; a third, "screen" electrode; and an additional, "deflection" electrode, which together with the screen electrode modulates ion flow to an imaging surface. Ions of a given polarity are attracted toward the imaging surface by an accelerating field resulting from a direct current potential of the control electrode. The screen electrode is maintained at a screen potential to control passage of ions through one or more apertures therein, while a further, deflection potential applied to the deflection electrode provides an additional level of control over the size, shape and location of the resulting electrostatic images. The deflection electrode may take the form of a conductive member on one side of the ion path, or two or more conductors straddling this path. This arrangement provides an additional level of multiplexing, simplifies the requirements of electronic drive circuitry, and improves image definition.