*: This page refers only to the old 1 CCD configuration of FORS2 (before March 22, 2002). The data for the mosaic of two MIT CCDs can be found here

Modes

Parameters are measured for all four CCD modes: - high gain 1 and 4port readout; low gain, 1port and 4port readout; binning always 1x1.

Parameters

Median level: median bias level.

Structure: sigma (s_A) is measured in the master; the read noise is subtracted geometrically. Ideally this number should be zero. Real values are below 1 ADU.

Sigma DA: fractional difference between median level in port D and A. This value is applicable for 4port readout only.

Read noise: the difference between values in raw files and master files controls the efficiency of the master creation process. The values for master files should be lower than those for raw files by a factor of (4...5)^-1/2 since typically 4-5 raw files are engaged in the master creation process. The broken line in plot 4 marks this nominal value.

parameter procedure applicable typical values plot** bias level (median) B (ADU) median across port A window raw/master high gain*: 225 +/- 5 ADU low gain: 245 +/- 3 ADU 1 structure sstruct (ADU) sstruct in port A window; sstruct = (sA2-sr2)1/2 master high gain: 0.11ADU low gain: 0.06 ADU 2a fractional port difference sCD (%) sCD: fraction (sC - sD)/sC raw/master, 4port only 0 - 8% 2b read noise sr (ADU) in raw file s in 100x100 pixels window raw high gain: 2.88 ADU *** low gain: 2.17 ADU *** 3 read noise sr (ADU) in master file s in 100x100 pixels window master high, low gain: raw/51/2 ADU 4

* actual gain values (since October 1999): high gain = 1.9 e^-/ADU, low gain = 2.7 e^-/ADU.
** numbers in plot
*** nominal values for port A (FORS Manual P77): 2.8 ADU (high), 2.1 ADU (low)