From kashik@zone.mtk.nao.ac.jp Thu Apr  3 07:11:47 1997
Date: Mon, 15 Jul 1996 13:25:39 +0900
From: Nobunari Kashikawa <kashik@zone.mtk.nao.ac.jp>
To: rgm@ast.cam.ac.uk, karkut@ast.cam.ac.uk, mike@ast.cam.ac.uk
Cc: kashik@zone.mtk.nao.ac.jp
Subject: MCCD optical center 


Dear all,

Currently, the optical center is defined as pixel position x-y on 
chip44.

#define XCEN 1459.5
#define YCEN 1919.5

And the fundamental equation which we adopt for the collection of 
optical distortion is as follows;
(these are described in the sorce file of "clean_wht.c" as a comment) 

 *	WHT Prime focuse distortion
 *
 *	Rtrue = k1 * Rfp + k2 * Rfp^3,
 *
 *	where k1= 17.57 arcsec/mm and k2= -4.1185E-5 arcsec/mm^3
 *
 *	This relation can be represented in terms of pix# to arcsec as
 *
 *	Rtrue = k1 * Rpix + k2 * Rpix^3,
 *
 *	where k1= 0.21084 arcsec/pix and k2= -7.116768E-11 arcsec/pix^3
 *
 *	For data analysis, the next fomular between physical pixel# and
 *	corrected vertual pixel# is more useful. ("pixel" here means
 *	the radious of a pixel in the scale of pixel.)
 *
 *	Rpix_true= k1 * Rpix + k2 * Rpix^3
 *
 *	where k1= 1 and k2= -3.3754354E-10
 *
 *
 *	The original parameter k1 and k2 are given in the WHT Prime manual.

regards,
Nobunari