FOCAS Facts Sheets

Introduction

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General

Location	SUBARU telescope Cassegrain focus
Observing modes	Imaging, (Multi-) Spectroscopy, Polarimetry
Calibration unit	Telescope CAL unit (Th-Ar)
Instrument Exchange	Auto exchanger (CIAX)

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Optics

Overall Layout	<------- Z+
Lenses	8 groups 14 lenses
Optimized wavelength	365-900nm
FOV	6 arcmin diameter
Total length (Cass. foc. to camera foc.)	1800mm
Transmission	80 (420-900nm)
Pupil diameter	90mm
f(collimator)	1097.7mm
f(camera)	329.4mm
Reduce rate	~3/10
RMS diameter (white)	16micron (on axis), 21micron (edge of the FOV)
Coatings	reflection rate less than 1%
Grisms	8 planned, 4 available R=250~1000 for 0.4 arcsec slits
Filters	Broad band: U, B, V, R, I Narrow band: 8 Order sorting: 4
ADC	The telescope Cassegrain unit contains an ADC unit. FOCAS uses the ADC unless you need the U data (since ADC has low UV transmission).

Detector

CCD/CCD controller/Dewer cooler

Picture of CCDs
CCD	MIT 4KX2K 3-side buttable CCD X 2mosaic Thinned, back-illuminated 15micron pixel
Image scale	~0.1 arcsec/pix
CCD readout electronics	MFRONT
CCD readout method	Integrated double sampling
Readout modes	Read area Whole: Whole CCD area Part: Read only around slits Read speed Normal read-out for lower noise readout (5e-) Fast read-out with larger noise (10e-) ADU/electron conversion factor change according to the read speed
Readout time	15~180 sec depending on read-out mode
CCD control	Messia III -> Messia V (from 2003 Summer)
Cooler	5W Staring

Grism specifications

Name	groove	dispersion (at 550 nm)	center	resolution R	comment
	(gr/mm)	(A/pix)	A	(at slitwidth=0.4arcsec)
75	75	5.46	6500	250	very low-disp., available
150	150	2.72	6500	500	low-disp., available
300B	300	1.34	5500	1000	middle-disp.(blue), available
300R	300	1.34	8000	1000	middle-disp.(red), available
	600	0.64	4300	2500	high-disp.(V), not ready
600-650 VPH	600	0.63	6550	2500	high-disp.(G)
	600	0.64	7700	2500	high-disp.(R), not ready
	600	0.64	9200	2500	high-disp.(red), not ready
Echelle	175	0.63	6600 (2nd) 9300 (2nd)	2500 2500	Echelle; only single-order mode is available

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Overall Hardware

Scale	2m(d) X 2m(h)
Weight	~2t
Flexure on 1 hr. exp.	~1pix
Filter wheels	Three wheels Two tilted, below the grism for general use One parallel above the grism for Hartmann mask, etc. 7 filters each
Grism wheel	One wheel 5 grisms at a time
Wheel rotation time	~10 sec for changing to adjacent filter/grism. <1 min. to changing to any
Shutter	Movable plate within the collimated beam
Minimum exposure of shutter	0.3 sec, however >~1 sec exposure is recommended for better accuracy
Mechanical Layout around center section

MOS (Multi-Object Spectroscopy) Hardware

Method	fixed slit mask plate
Max # of plates at a time	10 in total, 2-3 are reserved for long slits and Hartmann tests
Typical slit # per a plate	100, depending on grisms/filters used
Slit figure	arbitrary typical slit width is 100micron
Slit cutting	diode-pumped YAG laser (installed at Summit)
Slit parallelism	less than 10micron
Straightness of slit edges	less than 10micron
Positioning accuracy of slit center	less than 3micron
Time for replacing plates	~30-60 sec, depending the slit position in slit stocker
Default slit plates	long-slit masks, grid masks for Hartmann test

Strokes & Control precision of each component
(POL mode is not available yet)

Component	strokes	precision
Supplemental filter wheel	360 deg	90"
Wave plate wheel	360 deg	90"
Wave plate rotation	360 deg	90"
Polarizer slide	200-300mm	0.1mm
Grism wheel	360 deg	30"
Filter wheel	360 deg	600"
Dewar adjustments (XY direction)	1mm	3micron
Dewar adjustments (Z direction)	1mm	5micron

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Control System

Element modules

17 local control units 1 on-board WS, local control software 1 (or 2) control-building WS Multi-process RPC-connected softwares for multitasked operating GUI based interface Connected to SOSS system