==========================================================
 Pupil stop positioning repeatibility
 

 Test performed by Simon Rees and Paul Jolley (6/3/2003)
 Images analyzed by Almudena Zurita
 ==========================================================
 The test consisted on repeating movements of the pupil stop
 wheel between two positions at both sides of the reference
 pupil stop (cass-s). The pupil imager was in all the time,
 allowing an easy measurement of drift between images. An image 
 was taken everytime the cass-s pupil stop was in the beam.

  cass-s -- reference image
  cass-k
  cass-s -- second image
  ker
  cass-s --thrid image
 
  cass-s pupil stop: external radius: 500 pix
                     internal radius: ~135 pix


The table below contains the run number and the position of
the center of the cass-s pupil stop on the detector.

------------------------
Image           x     y     
              (pix) (pix)
------------------------
r579166.fit    499   526
r579167.fit    499   526
r579168.fit    497   526
r579169.fit    497   526
r579170.fit    495   526
r579171.fit    492   526
r579172.fit    492   526
r579173.fit    489   526
r579174.fit    489   526 
r579175.fit    484   526 
r579176.fit    485   526 
r579177.fit    481   526
r579178.fit    482   526
r579179.fit    476   526
r579180.fit    477   526
r579181.fit    476   526
r579182.fit    476   526
r579183.fit    474   526 


Clear evidence of drift.
Images analized with ds9 (to find centroid) and later with 'area.pro' in IDL.
See plot: Pstop.repeat.20030306.ps