1.2 Which Instrument to Use: WFPC2, ACS, NICMOS, or STIS?

In this section we compare briefly the performance of HST instruments with imaging capability in the UV to near-IR spectral range. These instruments include WFPC2 and STIS, as well as NICMOS, which was revived through the installation of the cryo-cooler, and the Advanced Camera for Surveys (ACS), which was installed during the HST Servicing Mission 3b1. Important imaging parameters for all instruments are summarized in Table 1.1.

Table 1.1: Comparison of WFPC2, ACS, NICMOS, and STIS Instrumental Imaging Parameters.

Parameter	WFPC2	ACS	NICMOS	STIS
Wavelength range	1150Å - 11,000Å	WFC: 3700 Å - 11000 Å HRC: 2000 Å - 11000 Å SBC: 1150 Å - 1700 Å	8000Å - 25,000Å	FUV-MAMA: 1150Å - 1700Å NUV-MAMA: 1700Å - 3100Å CCD: 2000Å - 11,000Å
Detector	Si CCDs	CCDs (WFC, HRC) MAMA (SBC)	HgCdTe arrays	CCD, MAMAs
Image Format	4 x 800 x 800	WFC: 2 butted 2048x4096 HRC: 1024x1024 SBC: 1024x1024	3 x 256 x 256	1024 x 1024
Field-of-view and pixel size	150" x 150" @ 0.1" /pix 34"x 34" @ 0.046"/pix (1)	WFC: 202"x202" @0.05" /pix HRC: 29"x26" @0.028"x0.025" /pix SBC: 35"x31" @0.033"x0.030" /pix	NIC1: 11"x 11" @ 0.043" /pix NIC2: 19" x 19" @ 0.075" /pix NIC3: 51" x 51" @ 0.2" /pix	MAMAs: 25" x 25" @ 0.024"/pix CCD: 51" x 51" @ 0.05" /pix (2)
Read noise	5 e-	WFC: 5 e- HRC: 4.7 e- SBC: 0 e-	30 e-	MAMAs: 0 e- CCD: 5.4e-
Dark current	0.002[WF2] - 0.006[PC] e- /s/pix	WFC: 0.002 e-/s/pix HRC: 0.0025 e-/s/pix SBC: 1.2x10-5 e-/s/pix	<0.1 e- /s/pix	NUV-MAMA: 0.0001 e- /s/pix FUV-MAMA: 7x10-6 e- /s/pix CCD: 0.004 e- /s/pix
Saturation	53,000 e-	WFC: 80,000 e- HRC: 140,000 e- SBC: 100 counts/s/pix	200,000 e-	MAMAs: 100 counts/s/pix CCD: 140,000 e-

1"L"-shaped field-of-view using 3 CCDs with 0.1" pixels, and one CCD with 0.046" pixels. 2Field-of-view is up to 51" x 51" if no filter is used, and down to 12" x 12" for some neutral density filters.