The background frames consist of the dominating detector dark current 
(monitored by the IFS dark level plot) and a small component originating from the instrument. 
The reported QC parameters cover 
the instrumental background radiation plus the dark level of the detector. 
The background has a minor dependenece on the CPI dichroic
which can be INS4.OPTI13.NAME=DIC_H or DIC_K and a major dependence on the
IFS bench temperature.