20100921UT
As in 20100919UT
several sequences of 10 bias separated by increasing time spans
were exposed.
Apparently, due to the dark tape in the spacers space,
this time no strange high counts are observed in the first bias in a row
indicating that the light contamination was diminished dramatically.
However, for a long enough time between exposures and enough light intensity
you may saturate the CCD.
Discussing with DLT, it seems that during CTIO 1m runs Ricardo Schmidt
ran some kind of wipe out before and after exposures, so that this
special effects wouldn't appear on registered data.
Such wipe out needs to be added to the PreCam CCD exposure procedure,
since it seems that the CCD keeps integrating all time,
regardless of exposing of not.
Note that if light leak is not a big issue for bias we still have to understand
why astronomical sources appear in the bias in the middle of the night as
described in Electronics-20100917UT and 20090920UT.
And how to deal with Cosmic rays that appear also in the bias,
regardless how quick the previous bias exposure was taken (which work
as a type of wipe out).