Re: CCD Charge clearring, is it required?

[Tom Droege <droege@wwa.com>]

Reading out the CCD clears it, so the clear operation is 
something you only do at the start of the evenings runs,
or if you have been off for a while for some reason.  The 
longer you are off, the more charge accumulates.  When
things get really saturated, then you have to clear several
times.  The charge ends up in funny places on the chip and
it takes a while to migrate to where it can be cleared.  At
least this is what I have found experimentally.  Experts 
can comment.

This is one great advantage of the drift scan operation
over picture mode.  After a few drift scans, the charge 
conditions settle down, and the constant scanning at
constant intervals means you get very repeatable line
to line results.  I give up drift scanning on the Mark IVs
with reluctance.

My view is that in picture mode, you want to take pictures
at very regular intervals if you want comparable results.

Tom Droege

To: tass@wwa.com
Subject: Re: CCD Charge clearing, is it required?