Space Telescope Science Institute   5.3 Wide Field Optical CCD Imaging  5.4 High-Resolution Optical and UV Imaging

5.3.1 Filter Set


WFPC2 and Johnson-Cousins filters

All of the most commonly used WFPC2 filters are included in the ACS filter set. In addition to a medium and a broad V band filter (F550M and F606W), there is a complete Johnson-Cousins BVI set (F435W, F555W, F814W).

Sloan Digital Sky Survey filters

The Sloan Digital Sky Survey (SDSS) griz filter set (F475W, F625W, F775W, F850LP) is designed to provide high throughput for the wavelengths of interest and excellent rejection of out-of-band wavelengths. The filters were designed to provide wide, non-overlapping filter bands that cover the entire range of CCD sensitivity from blue to near-IR wavelengths.

Narrow Band filters

The H (F658N), [] (F502N), and [NII] (F660N) narrow band filters are full-size, and can be used with both the WFC and HRC.

Ramp filters

ACS includes a complete set of ramp filters that provide full coverage of the WFC wavelength range at 2% and 9% bandwidth. Each ramp filter consists of three segments. The inner and outer filter segments can be used with the WFC only, while the central segments can be used by both WFC and HRC. Unlike the WFPC2, where the desired wavelength is achieved by offsetting the telescope, the wavelength of ACS ramps is selected by rotating the filter while the target is positioned in one of the pre-defined apertures. The monochromatic field of view of the ramp filters is approximately 40 by 80 arcseconds. Details of how to use the ramp filters are given in Section 7.7.2.

Polarizer filters

The WFC/HRC filter wheels contain polarizers with pass directions spaced by 60º, optimized for both the UV (POL0UV, POL60UV, and POL120UV) and the visible (POL0V, POL60V, and POL120V). All the polarizer filters are sized for the HRC field of view. They induce vignetting when used with the WFC, for which the FOV will be about 72 by 72arcseconds. More information on the use of the polarizers is given in Chapter 6.

Grism and Prism

The CCD channels also have a grism (G800L) for use with both WFC and HRC from 5500 Ċ to 11,000 Ċ, and a prism (PR200L) for use with the HRC from 1600 Ċ to 3500 Ċ. These are described more fully in Chapter 6.


 5.3 Wide Field Optical CCD Imaging  5.4 High-Resolution Optical and UV Imaging
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