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 Figures
5.8 (limiting magnitude for point sources) and
Figure 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 x 202 arcsec
2) is considerably larger than that of WFC3/UVIS (162 x 162 arcsec
2). WFC3/UVIS is therefore 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 ~ 400 nm, so ACS/WFC should be used if greater sensitivity at red wavelengths is important. However, users should also consider ACS’s generally lower charge-transfer efficiency (CTE) compared to WFC3/UVIS, and its increased number of hot pixels caused by its lengthy exposure to
HST’s trapped radiation environment. (See
Section 4.3.7 for details.)
