An interferometer includes a first assembly having a base, a beam splitter assembly to split light into first and second portions, and a fixed mirror for reflecting the first portion of light; and a second assembly movable with respect to the first assembly, and having first and second scan carriages, and a movable mirror connected to the second scan carriage for reflecting the second portion of light. The beam splitter assembly combines the reflected first and second portions of light into a recombined radiation beam. Inner bearing flexures enable movement of the first scan carriage relative to the base, and outer bearing flexures enable movement of the second scan carriage relative to the first scan carriage, such that a plane containing the movable mirror is maintained parallel to multiple planes containing the movable mirror at respective distances between the second and first assemblies during scan movement of the movable mirror.