Set-up of the FIRST-18 instrument. The injection part of the set-up, up to the fiber bundle, is basically unchanged compared to the previous version of the instrument. The recombination part on the other hand has been duplicated. The EMCCD dedicated to the measurement of the transmitted flux during the optimization procedure has also been depicted. The mirrors drawn as gray lines (just after the V-grooves and microlens arrays) are removable from the light path. Inset a) illustrates the resulting beam shapes after the anamorphic system. Inset b) is a side view of the recombination of the beams (only three beams out of nine are represented). SM: Segmented mirror. PBS: Polarizing beam splitter. μL: Microlens array. FB: Fiber bundle. VG: V-groove. P: Dispersing prism.