Re: correct bias usage and using "Search the TASS Site"

[hjohnson@pluto.njcc.com (Herbert R Johnson)]

On Fri, 3 Aug 2001 12:30:12 -0600 , "Creager, Robert S" <CreagRS@LOUISVILLE.STORTEK.COM> wrote:
*>
*>Arne,
*>
*>I would never accuse you of being dense any day, but I have been accused of
*>obfuscating the obvious regularly.
*>
*>Column 3 was once determined to be a good covered column, as it varied
*>little between exposures of the same length.  Typically, I see variances
*>between column 3 of less than 20 ADU (between dark/object), so this was
*>chosen (by folks before me, I just verified/used it) as a 'scaling' column
*>to offset small timing irregularities.
*>

 There is a TASS Tech Note on older Mark IV images which reviews
 this subject. I am rushed at the moment so I can't offer a pointer
 to it, I believe I authored (edited) it, so check my Mark IV
 TN's first. Other dark columns are also considered.

 You should verify to your own satisfaction that the covered column of
 your choice correlates to the dark current levels in the images. My
 Tech Note on Mark IV dark current provides some simple tools for this.
 The note speaks to these issues.

 Tom said he is likely to change these covered columns; this may
 change which columns offer useful info.

 Finally: there has been a TREMENDOUS history of prior discussion about
 dark current and sky background. A somewhat tedious search of TASS
 email via the TASS Web site will uncover some of it. My TN's may have
 some referernces to that discussion; other TN's will name and date
 the interest of other people. These will help in a search. That is
 what the email archive and TN's are for.

Herb Johnson

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