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Re: CCD Charge clearing, is it required?
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- Date: Wed, 28 Jan 98 08:32:37 -0700
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Chris asked if 40 seconds was unreasonable for clearing the CCD (which it
is), and Roland asked if you could just do vertical transfers with one
serial readout at the end.
Usually, to clear a CCD of charge, you need to transfer all charge to
the reset node on the CCD. The usual way is to do several vertical shifts
(like binning), and then do a binned serial readout with reset enabled and
no ADC convert. I think 1000 vertical transfers is a little excessive, as
the trick is to not saturate the serial register 'pixels' terribly. I
usually do tens of vertical shifts plus tens of serial bins for a 2048 CCD,
and then do 1-3 of these 'wipe' operations before an actual exposure. For
normal images, where there are just a few leftover remnants of stars to
remove, this procedure works well.
This should just be an extra clocking scheme to stick in the EPROM -- right,
Tom? The harder one to implement is what is commonly referred to as an
erase cycle, used to clear the chip of any residual images.