2.2 Comparison of WFC and UVIS

The UVIS channel of the Wide Field Camera 3 complements ACS/WFC over wavelengths ~3700 Å to 10,000 Å. Observers must determine which instrument is more appropriate for their science from the perspectives of field of view, pixel size, throughput, and filter availability. Table 2.2, Figure 2.1 and Figure 2.2 show these characteristics for each instrument. See also Figures 5.8 (limiting magnitude for point sources) and 5.9 (limiting magnitude for extended sources). ACS/WFC has a larger pixel scale (0.05 arcsec/pixel) than WFC3/UVIS (0.04 arcsec/pixel), so the field of view of ACS/WFC (202 × 202 arcsec²) is considerably larger than that of WFC3/UVIS (162 × 162 arcsec²). WFC3/UVIS may therefore be preferred if angular resolution is more important than field of view. On the other hand, ACS/WFC is more sensitive than WFC3/UVIS at wavelengths longward of ~4000 Å, so ACS/WFC is recommended if greater sensitivity at red wavelengths is important. Due to the trapped radiation environment of HST, both ACS/WFC and WFC3/UVIS suffer from similar charge transfer efficiency (CTE) losses at this point in their lifetimes. See Section 4.3.8 for details. It is also possible to use both ACS/WFC and WFC3/UVIS in parallel. The separation of the two cameras is ~360" (see Figure 3.1).

Table 2.2: Comparison of wavelength coverage, pixel scales, and fields of view of ACS and WFC3/UVIS. HRC is no longer available. More information can be found at the SIAF website.