5.1 Imaging Overview

HRC has been unavailable since January 2007. Information regarding HRC is provided for archival purposes.

ACS has been used to obtain images through a variety of optical and ultraviolet filters. 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 × 72 arcsec2 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.

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, see Figures 3.2 and 3.3. (Users need not specify CLEAR in their HST proposals.) For SBC imaging, the single filter wheel is rotated to the desired position. Every third spot (#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. Tables 5.15.2, and 5.3 summarize the filters available for imaging with each channel. Figures 5.1 through 5.6 show the filter transmission curves. Figures 5.10 and 5.11 show the location of the filters in each filter wheel. Figure 5.7 shows the integrated system throughputs. Please visit the ACS System Throughputs webpage or refer to Chapter 10 for a full catalog of the ACS filter throughputs.

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, each of which can be used with the WFC while only the middle segment was used with the HRC. See Table 5.2 for the list of available ramp filters. 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] [a]

POL60UV

2000 to 6000

60° UV polarizer

HRC[/WFC] [a]

POL120UV

2000 to 6000

120° UV polarizer

HRC[/WFC] [a]

F892N

8917

154

Methane (2%)

HRC[/WFC] [a]

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

a [/WFC] indicates that polarizer filters, designed for the HRC field of view, induces vignetting when used with the WFC, producing a 72  × 72 arcsec2 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%1

[OII] Ramp—middle segment

WFC/HRC

FR423N

4050 to 4420

2% [a]

[OII] Ramp—inner segment

WFC

FR462N

4420 to 4820

2% [a]

[OII] Ramp—outer segment

WFC

F435W

4297

1038

Johnson B

WFC/HRC

FR656N

6270 to 6850

2% [a]

Hα Ramp—middle segment

WFC/HRC

FR716N

6850 to 7470

2% [a]

Hα Ramp—inner segment

WFC

FR782N

7470 to 8160

2% [a]

Hα Ramp—outer segment

WFC

POL0V

4000 to 8000

0° Visible Polarizer

HRC[/WFC] [b]

F330W

3354

588

HRC U

HRC

POL60V

4000 to 8000

60° Visible Polarizer

HRC[/WFC] [b]

F250W

2696

549

Near-UV broadband

HRC

POL120V

4000 to 8000

120° Visible Polarizer

HRC[/WFC] [b]

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% [a]

Broad Ramp—middle segment

WFC/HRC

FR853N

8160 to 8910

2% [a]

IR Ramp—inner segment

WFC

FR931N

8910 to 9720

2% [a]

IR Ramp—outer segment

WFC

FR459M

3810 to 5370

9% [a]

Broad Ramp—middle segment

WFC/HRC

FR647M

5370 to 7570

9% [a]

Broad Ramp—inner segment

WFC

FR1016N

9720 to 10,610

2% [a]

IR Ramp—outer segment

WFC

FR505N

4820 to 5270

2% [a]

[OIII] Ramp—middle segment

WFC/HRC

FR551N

5270 to 5750

2% [a]

[OIII] Ramp—inner segment

WFC

FR601N

5750 to 6270

2% [a]

[OIII] Ramp—outer segment

WFC

aThe width of the ramp filters is a percentage relative to the central wavelength of the bandpass, Δλ/λ.
b [/WFC] indicates that polarizer filters, designed for the HRC field of view, induces vignetting when used with the WFC, producing a 72  × 72 arcsec2 field of view.

Table 5.3: ACS SBC filter complement.

Filter name

Description

F115LP

MgF2 (1150 Å longpass)

F125LP

CavF2 (1250 Å longpass)

F140LP

BaF2 (1400 Å longpass)

F150LP

Crystal quartz (1500 Å longpass)

F165LP

Fused Silica (1650 Å longpass)

F122M

Lyα (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 the ACS narrow and medium band ramp filters. The open squares are the 4 WFPC2 ramp filters. For each of the ACS filters, the peak throughput for the central eleven wavelength points is plotted. For the WFPC2 filters, the peak throughput for every 100 Å within the field of view of any of the 4 chips and for a 0° filter rotation angle (as mapped in Figures 3.4 and 3.5 of the WFPC2 Instrument Handbook) is plotted.