5.1 Imaging Overview

HRC is not available in Cycle 19. Information regarding HRC is provided for archival purposes.

ACS has been used to obtain images through a variety of optical and ultraviolet filters. For WFC and HRC imaging, the desired filter in one filter wheel is rotated into position and a CLEAR aperture in the other filter wheel is automatically selected. (Users need not specify CLEAR in their HST proposals.) For SBC imaging, the single filter wheel is rotated to the desired position. Every third slot (#1, 4, 7, 10) in the SBC filter wheel is opaque, so the wheel must only be rotated to an adjacent slot to block the beam if a bright object limit violation occurs.Table 5.1,Table 5.2, and Table 5.3 summarize the filters available for imaging with each channel. Figures 5.1 through 5.6 show the filter transmission curves, and Figure 5.7 shows the integrated system throughputs.

The CCD filter wheels contain filters of two different sizes. Some filters (F435W, F475W, F502N, F550M, F555W, F606W, F625W, F658N, F660N, F775W, F814W, F850LP, and, G800L) are full-sized filters that can be used with both WFC and HRC. Others (F220W, F250W, F330W, F344N, F892N, POL0UV, POL60UV, POL120UV, POL0V, POL60V, POL120V, and PR200L) are smaller, giving a full unvignetted field of view when used with the HRC, but a vignetted field of view of only 72 â 72 arcseconds2 when used with the WFC. Use of the small UV filters with WFC is not supported due to the unpredictable behavior of the silver coating shortward of 4000 å.

The ACS ramp filters are designed to allow narrow or medium band imaging centered at an arbitrary wavelength. Each ramp filter is divided into three segments, of which only the middle segment was used with the HRC. More information is available in Section 7.3.1.

Filterless WFC or HRC is available, but unsupported, by specifying CLEAR as the filter name. Rough wavelengths and bandwidths for CLEAR imaging are listed in Table 5.1. CLEAR imaging yields significantly degraded WFC PSFs, but only slightly degraded HRC PSFs. See ACS ISR 2003-03 for more details about CLEAR imaging.

Table 5.1: ACS WFC/HRC filters in Filter Wheel #1.

(HRC information is provided for archival purposes only.)

Filter name	Central wavelength (å)	Width (å)	Description	Camera
CLEAR	6200	5200	Clear aperture	WFC/HRC
F555W	5346	1193	Johnson V	WFC/HRC
F775W	7764	1528	SDSS i	WFC/HRC
F625W	6318	1442	SDSS r	WFC/HRC
F550M	5580	547	Narrow V	WFC/HRC
F850LP	9445	1229	SDSS z	WFC/HRC
POL0UV	2000 to 6000	-	0° UV polarizer	HRC[/WFC]1
POL60UV	2000 to 6000	-	60° UV polarizer	HRC[/WFC]1
POL120UV	2000 to 6000	-	120° UV polarizer	HRC[/WFC]1
F892N	8917	154	Methane (2%)	HRC[/WFC]1
F606W	5907	2342	Broad V	WFC/HRC
F502N	5022	57	[OIII] (1%)	WFC/HRC
G800L	5800 to 11,000	-	Grism (R~100)	WFC/HRC
F658N	6584	78	Hα (1%)	WFC/HRC
F475W	4760	1458	SDSS g	WFC/HRC

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1

[/WFC] indicates that polarizer filters, designed for the HRC field of view, induces vignetting when used with the WFC, producing a 72 by 72 arcsecond2 field of view.

Table 5.2: ACS WFC/HRC filters in Filter Wheel #2.

(Information regarding the HRC is provided for archival purposes only.).

Filter name	Central wavelength (å)	Width (å)	Description	Camera
CLEAR	6000	5200	Clear aperture	WFC/HRC
F660N	6602	40	[NII] (1%)	WFC/HRC
F814W	8333	2511	Broad I	WFC/HRC
FR388N	3710 to 4050	2%	[OII] Ramp—middle segment	WFC/HRC
FR423N	4050 to 4420	2%	[OII] Ramp—inner segment	WFC
FR462N	4420 to 4820	2%	[OII] Ramp—outer segment	WFC
F435W	4297	1038	Johnson B	WFC/HRC
FR656N	6270 to 6850	2%	Hα Ramp—middle segment	WFC/HRC
FR716N	6850 to 7470	2%	Hα Ramp—inner segment	WFC
FR782N	7470 to 8160	2%	Hα Ramp—outer segment	WFC
POL0V	4000 to 8000	-	0° Visible Polarizer	HRC[/WFC]1
F330W	3354	588	HRC U	HRC
POL60V	4000 to 8000	-	60° Visible Polarizer	HRC[/WFC]1
F250W	2696	549	Near-UV broadband	HRC
POL120V	4000 to 8000	-	120° Visible Polarizer	HRC[/WFC]1
PR200L	2000 to 4000	-	NUV Prism (R~100 @ 200 nm)	HRC
F344N	3434	60	Ne V (2%)	HRC
F220W	2228	485	Near-UV broadband	HRC
FR914M	7570 to 10,710	9%	Broad Ramp—middle segment	WFC/HRC
FR853N	8160 to 8910	2%	IR Ramp—inner segment	WFC
FR931N	8910 to 9720	2%	IR Ramp—outer segment	WFC
FR459M	3810 to 5370	9%	Broad Ramp—middle segment	WFC/HRC
FR647M	5370 to 7570	9%	Broad Ramp—inner segment	WFC
FR1016N	9720 to 10,610	2%	IR Ramp—outer segment	WFC
FR505N	4820 to 5270	2%	[OIII] Ramp—middle segment	WFC/HRC
FR551N	5270 to 5750	2%	[OIII] Ramp—inner segment	WFC
FR601N	5750 to 6270	2%	[OIII] Ramp—outer segment	WFC

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1

[/WFC] indicates that polarizer filters, designed for the HRC field of view, induces vignetting when used with the WFC, producing a 72 by 72 arcsecond2 field of view.

Table 5.3: ACS SBC filter complement.

Filter name	Description
F115LP	MgF2 (1150 å longpass)
F125LP	CaF2 (1250 å longpass)
F140LP	BaF2 (1400 å longpass)
F150LP	Crystal quartz (1500 å longpass)
F165LP	Fused Silica (1650 å longpass)
F122M	Ly-α (λ = 1200 å, Δλ = 60 å)
PR110L	LiF Prism (R~100)
PR130L	CaF2 Prism (R~100)

Figure 5.1: ACS broad-band filters.

Figure 5.2: ACS SDSS filters.

Figure 5.3: ACS UV and medium-band filters.

Figure 5.4: ACS narrow band filters.

Figure 5.5: ACS SBC filters.

Figure 5.6: Comparison between the ACS and WFPC2 ramp filters.

The crosses and open circles are for the ACS narrow and medium band ramps. The open squares are for the 4 WFPC2 ramps. For each of the ACS ramps the peak throughput that was calculated for eleven central wavelength values is plotted. For the WFPC2 ramps, the peak throughput calculated every 100 å within the field of view of any of the 4 chips, and a 0 filter rotation angle (as mapped in Figures 3.4 and 3.5 of the WFPC2 Instrument Handbook, version 3.0), are plotted.