Abstract: A high-voltage insulation device (300) for use in a charged-particle optical apparatus comprises a plurality of rigid pillars (320) made of electrically insulating material. These pillars (320) are arranged around a central passage (310) which traverses the insulating device along its longitudinal axis (L), and the two ends of each pillar are configured to be respectively fixed to two separate electrostatic housings (221, 231) of the charged-particle optical apparatus by means of two respective end plates (311, 312), with the pillars (320) being oriented at an angle so as to be inclined with regard to said longitudinal axis (L). Advantageously, the pillars are mechanically adjustable with regard to their effective length, and each pillar (320) is arranged outside the central passage with its two ends at either of the first and second end plates (311, 312), preferably in a zig-zag arrangement.