bin sets the x and y binning factors for subsequent CCD readouts (it has no effect on readouts currently in progress). The factors must be integers in the range 1..10 inclusive and may be different on each axis. Where more than one CCD (or more than one CCD readout-point) is involved in each observation, as with the INT's mosaic camera, the same binnning factors are used for all the readout points of all the CCDs.
bin x-factor y-factor
Set 4 by 2 binning:
bin 4 2
Turn off binning:
bin 1 1