  The Prime Focus Spectrograph (PFS) is a new optical/near-infrared multi-fiber
spectrograph design for the prime focus of the 8.2m Subaru telescope. PFS will
cover 1.3 degree diameter field with 2394 fibers to complement the imaging
capability of Hyper SuprimeCam (HSC). The prime focus unit of PFS called Prime
Focus Instrument (PFI) provides the interface with the top structure of Subaru
telescope and also accommodates the optical bench in which Cobra fiber
positioners are located. In addition, the acquisition and guiding (A&G)
cameras, the optical fiber positioner system, the cable wrapper, the fiducial
fibers, illuminator, and viewer, the field element, and the telemetry system
are located inside the PFI. The mechanical structure of the PFI was designed
with special care such that its deflections sufficiently match those of the HSC
Wide Field Corrector (WFC) so the fibers will stay on targets over the course
of the observations within the required accuracy.
