Top: view of the effect of the IFU. The central field is directly transmitted to form the central slitlet (blue) while each lateral field (in red and green) is reflected toward a pair of spherical mirrors, and realigned at the end of the central slice to form the exit slit. Bottom: the field before (left) and after the IFU (right). The IFU acts such that the lateral fields are rotated. The two white slots are not real gaps but just guides to help visualize the top and the bottom of each slice in the drawing.