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).