Space Telescope Science Institute   7.6.1 WFC Gain  7.7 ACS Apertures

7.6.2 HRC Gain


GAINs 2 and 4 are fully supported for the HRC, and analogous to the supported WFC values provide a low readout noise case and a GAIN that provides sampling of the physical full well depth.

GAIN=4 on the HRC, which is needed if high dynamic range on the bright end is desired, does not provide critical sampling of the readout noise. Not only is the readout noise penalty in going from GAIN=2 to 4 non-trivial, but background estimation will be less robust without critical noise sampling. As with WFC, when the full well depth is sampled with GAIN=4 the detector response remains accurately linear up to and even well beyond saturation. Compression is not an issue for the small HRC images, therefore use of the unsupported GAIN=8 is not anticipated. GAIN=1 is available-but-unsupported, but the very modest improvement of readout noise in comparison to GAIN=2 (< 0.2 e- higher rms) seems unlikely to present compelling need for its use.


 7.6.1 WFC Gain  7.7 ACS Apertures
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