4D mounts provide highly repeatable tip and tilt of the test and/or reference optics. The mounts accept either sling-mounted flats, which are set in removable handling cells that provide precision, 360-degree rotation, or potted flats which can be rotated in 60 degree increments.

The 4D phase-shifting tip/tilt mount includes a piezo-actuated phase shifter for shifting the reference temporal measurements when an aperture converter is employed. 

A range of transmission and return flats are available, with λ/10 or λ/20 wavefront quality.