a system for supporting and adjusting the position of an object in a vacuum includes inner and outer support rings that are connected by flexible mounts that are compliant along one axis and stiff along other axes , and drivers extending through the wall of the vacuum chamber that move the supports independently along their respective axes . at least the inner support is clamped after adjustment by a clamp that exerts a strong clamping pressure while exerting transverse force only less than a threshold selected to avoid motion after adjustment .