UIST: Engineering - IJ and JH Focus

History:

• June 2005: Installed new IJ and JH grisms in UIST; problem with Focus and wierd arcs (see previous page).
• December 2005: UIST warm - install 4pix and 2pix slits with 3mm spacers to try and bring IJ and JH spectra into focus.
• July 2006: UIST warm over summer. Use smaller spacers to improve focus. Also update OT so new slits available (to be released later in the year). 4pix slit+spacers now give ~4-5 pix resolution.

Jul 2005 - Normal/old slits (no spacers); new IJ and JH grisms

DAYTIME TESTING -

Arc Line width versus internal (array) focus:

IJ / 2-pix  foc = 1mm  FWHM = 15 pix   IJ / 4-pix  foc = 1mm  FWHM = 14.9 pix
            foc = 2mm  FWHM = 13 pix               foc = 2mm  FWHM = 13.1 pix
            foc = 3mm  FWHM = 11 pix               foc = 3mm  FWHM = 11.2 pix
            foc = 4mm  FWHM =  9 pix               foc = 4mm  FWHM =  9.5 pix
            foc = 5mm  FWHM =  7 pix               foc = 5mm  FWHM =  8.0 pix
                
            - Optimum focus @ 7.5mm                - Optimum focus @ 7.4mm

JH / 2-pix  foc = 1mm  FWHM =  5 pix   JH / 4-pix  foc = 1mm  FWHM = 5.6 pix
            foc = 2mm  FWHM =  5 pix               foc = 2mm  FWHM = 5.2 pix
            foc = 3mm  FWHM =  4 pix               foc = 3mm  FWHM = 4.8 pix
            foc = 4mm  FWHM =   --                 foc = 4mm  FWHM = 4.5 pix
            foc = 5mm  FWHM =  3 pix               foc = 5mm  FWHM = 4.3 pix 
       
            - Optimum focus @ 7.0mm                - Optimum focus @ 5.2mm

Width of BB spectrum thru the 2 pix pinhole versus internal (array) focus:

IJ / 2p-pin foc = 1mm  FWHM = 21.7 pix 
            foc = 2mm  FWHM = 19.5 pix 
            foc = 3mm  FWHM = 17.8 pix  
            foc = 4mm  FWHM = 15.5 pix 
            foc = 5mm  FWHM = 13.6 pix  

            - Optimum focus > 5.0mm 

JH / 2p-pin foc = 1mm  FWHM =  2.7 pix 
            foc = 2mm  FWHM =  2.0 pix 
            foc = 3mm  FWHM =  2.2 pix 
            foc = 4mm  FWHM =  2.8 pix
            foc = 5mm  FWHM =  4.0 pix   

            - Optimum focus ~ 2.4mm ?? check - first value bad?

The above tests "suggest" that the array needs to be focused beyond its current "high" limit of 5mm. Possible solution - move slits away from array!

Feb 2006 - New slits plus 3.5mm spacers; new IJ and JH grisms

DAYTIME TESTING -

Arc Line width versus internal (array) focus:

IJ / 2-pix+sp  foc = 1mm  FWHM =  5.8 pix   IJ / 4-pix+sp  foc = 1mm  FWHM =  6.3 pix
               foc = 2mm  FWHM =  6.0 pix                  foc = 2mm  FWHM =  6.6 pix
               foc = 3mm  FWHM =  6.7 pix                  foc = 3mm  FWHM =  7.4 pix
               foc = 4mm  FWHM =  7.6 pix                  foc = 4mm  FWHM =  8.2 pix
               foc = 5mm  FWHM =  8.5 pix                  foc = 5mm  FWHM =  9.2 pix

               - Optimum focus @ -1.0 mm                  - Optimum focus @ -1.0mm

JH / 2-pix+sp  foc = 1mm  FWHM =  2.7 pix   JH / 4-pix+sp  foc = 1mm  FWHM =  5.1 pix
               foc = 2mm  FWHM =  3.6 pix                  foc = 2mm  FWHM =  5.9 pix
               foc = 3mm  FWHM =  5.3 pix                  foc = 3mm  FWHM =  7.6 pix
               foc = 4mm  FWHM =  7.8 pix                  foc = 4mm  FWHM =  9.7 pix
               foc = 5mm  FWHM = 10.3 pix                  foc = 5mm  FWHM = 13.3 pix

               - Optimum focus @ 1.0 mm                   - Optimum focus = 0.5mm

On arc spectra, now see sharpest lines at a focus of around zero - i.e. at the other end of array travel! Below - comparison plots from the above data.

Comparison of old/no-spacer and new/3.5mm-spacer 4-pixel slits

IJ grism - bottom three plots show old 4pix slit at focii of 1,3 and 5mm (blue/green/red); top three plots show new 4pix slit + spacer at focii of 1,3 and 5mm (blue/green/red).	JH grism - bottom three plots show old 4pix slit at focii of 1,3 and 5mm; top three plots show new 4pix slit + spacer at focii of 1,3 and 5mm.

July 2006 - New slits plus 2.0mm spacers; new IJ and JH grisms

DAYTIME TESTING -

Arc spectra look a bit better. Established best focus of 2.0 for IJ and 4.0 for JH.

Comparison of old/no-spacer and new/2.0mm-spacer 4-pixel slits

IJ grism - bottom three plots show old 4pix slit at focii of 1,3 and 5mm (blue/green/red); top three plots show new 4pix slit + spacer at focii of 1,3 and 5mm (blue/green/red).	JH grism - bottom three plots show old 4pix slit at focii of 1,3 and 5mm; top three plots show new 4pix slit + spacer at focii of 1,3 and 5mm.

Note about black coating on new slits

The manufacturer had problems with the black coating on the new slits. However, this doesn't seem to have any effcet on the data. Comparing the new 4-pix (plus spacer - bad coating) with the old 4-pix (no spacer - good coating):

 IJ / old 4-pix     foc 5.0  Ave on sky background = -0.72, RMS=3.5  
                             Peak S/N on standard star spec ~ 600

 IJ / new 4-pix+sp  foc 5.0  Ave on sky background = -2.9, RMS=3.5  
                             Peak S/N on standard star spec ~ 600

 IJ / new 4-pix+sp  foc 0.5  Ave on sky background = -1.7, RMS=3.4  
                             Peak S/N on standard star spec ~ 750