FOCAS readout modes

FOCAS has a number of readout modes for on-chip binning of data. This can be useful to significantly improve the signal-to-noise ratio for faint objects, or where resolution (spatial and/or spectral) is not essential.

Note: Since 2003 September, longer readout time is required to reduce read noise.

Binning (spatial x spectral)	Readout time (s)	Image size
1 x 1	166	2047 x 4095
2 x 1	85	1023 x 4095
3 x 1	61	683 x 4095
4 x 1	49	512 x 4095
2 x 2	52	1023 x 2047
3 x 2	37	683 x 2047
4 x 2	29	512 x 2047
2 x 3	36	1023 x 1365
3 x 3	26	683 x 1365
4 x 3	20	512 x 1365
3 x 4	19	683 x 1023
4 x 4	15	512 x 1023

Some partial readout modes with either 1 x 1 or 2 x 2 binning are available for quicker target acquisition on slits.