Subject: Residual charge on the red chip

From: strauss@astro.Princeton.EDU

Submitted: Thu, 26 Nov 1998 00:49:34 -0500 (EST)

Message number: 70 (previous: 69, next: 71 up: Index)

Hello all,
  As all frequent users of DIS are aware, there is a nasty problem
with residual charge on the red chip.  If you have a bright star,
seen for example in imaging mode, and you are not careful to do a 
wipe of the chips, there can be a nasty streak of residual charge 
left behind on the next exposures, which can play havoc with faint
object spectroscopy.  This can be particularly nasty, if you have
just taken a focus frame on a bright star; this can ruin a subsequent
faint exposure.  We recommend therefore deliberately placing focus
stars on one side of the chip, not in the center, and being sure to
do a careful wipe of DIS before taking any spectra. 

			Michael Strauss

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