Subaru Telescope Dome Floor Wide Field Corrector Wide Field Corrector and Prime Focus Instrument Prime Focus Instrument PFI to Cobra COBRA module COBRA module Spectrograph Module Spectrograph Module Metrology Camera System Metrology Camera System

Instrumentation -- Technology of Prime Focus Spectrograph

The Subaru Prime Focus Spectrograph (PFS) is a spectrograph system with a fiber positioner system to be mounted at the prime focus of the Subaru telescope. The instrument allows simultaneous spectral observation of up to 2400 astronomical targets in a wide field of view of 1.3 degree diameter at a time.


Subaru Telescope

The Subaru Telescope is an 8.2-meter telescope at the 4,200m (12,460ft.) summit of Mauna Kea, Hawaii. Thanks to its photon-collecting power and wide field-of-view, Subaru Telescope enables PFS a panoramic and efficient spectroscopic survey of faint galaxies.

Wide Field Corrector(WFC)

WFC is the optical system consists of 7 lenses designed to correct imaging aberrations for Hyper Suprime-Cam(HSC). The first lens (the bottom most lens in right picture) is 820 mm (32inch) diameter wide effective area and the total lens system is 1845 mm (73inch) long.


The four-unit of spectrographs provide the simultaneous measurements of 2400 spectra. Each spectrograph has three independent channels separated by dichroics and covers a wide wavelength range from 0.38 micron to 1.26 micron.

Metrology Camera

Metrology Camera, attached to the Cassegrain Focus of Subaru Telescope, measures the positions of fibers on the Prime Focus. The camera takes the image of the all 2400 fibers with a single exposure.

Fiber System

The fiber system consists of 2400 optical fibers which relay light collected through the WFC at the focal plane to four spectrographs located in a room adjacent to the telescope. Each fibers is 65 meters in length and are assembled into four groupes providing 600 inputs to each spectrograph.

Fiber Positioner

Each optical fiber tip in an array of 2400 fibers, is controllable in-plane by the fiber positioner, nicknamed "Cobra." The patrol regions, Each 9.5mm in diameter, are packed in a hexagonal pattern with 8mm separation. The overlap between adjacent patrol regions enables 100% sky coverage of the hexagonal field.

Movie of a prototype of Fiber Positioner "Cobra"