A scanner includes a lens assembly comprising a lens having a lens axis and a positioning system to adjust a focal plane of the lens assembly. The positioning system includes an outer element, an inner element that houses the lens assembly, and a linear-motion bearing that couples the inner element to the outer element. The linear-motion bearing includes a first element coupling and a second element coupling. The linear-motion bearing provides a single degree of translational movement of the inner element along the lens axis.
