<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 98.1p1 release (March 2nd, 1998) originally by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>Flat-fielding</TITLE> <META NAME="description" CONTENT="Flat-fielding"> <META NAME="keywords" CONTENT="vol2"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <LINK REL="STYLESHEET" HREF="vol2.css"> <LINK REL="next" HREF="node704.html"> <LINK REL="previous" HREF="node702.html"> <LINK REL="up" HREF="node696.html"> <LINK REL="next" HREF="node704.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html10275" HREF="node704.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html10272" HREF="node696.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html10266" HREF="node702.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html10274" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html10276" HREF="node704.html">Wavelength calibration</A> <B> Up:</B> <A NAME="tex2html10273" HREF="node696.html">FEROS</A> <B> Previous:</B> <A NAME="tex2html10267" HREF="node702.html">Order extraction</A> <BR> <BR> <!--End of Navigation Panel--> <H1><A NAME="SECTION003770000000000000000"> Flat-fielding</A> </H1> <P> Since the flat-fields are also taken through the fiber, the FEROS spectra cannot reasonably be flat-fielded in a 2-D way. Instead the extracted spectra of the object and the flat-field lamp are divided to remove the pixel-to-pixel variations. This division also removes the blaze function of the echelle grating with good precision. However, this requires that the background subtraction is sufficiently accurate. The command corresponding is FLAT/FEROS. <P> <BR><HR> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
