Top: 3D drawing of the structure supporting the 4 polarizers of the instrument (WG_in, WG_out, WG_bs,L, WG_bs,R). Bottom: the frame integrated with all the optical components. The volume of the main body is 70 × 70 × 33 cm³. The protruding beam supports the linear motor that moves the folding-flat/lens assembly to exclude or include the MPI in the optical path of the OLIMPO instrument.