From ndouglas Mon Aug 23 21:44:49 1999
   
  phaseB.review
  =============
  
  A meeting was held during week 29 1999 (July 19 & 24) to review
  the status of the project following receipt of the phase B
  interim report. The intention was  to answer questions raised by the 
  report (produced by RSAA) in order to allow RSAA complete phase B.
  
  Present: MA, ND, KK, KCF, RM (and on July 19 Aaron Romanowsky)
  
  action item for ..............................................XX
  
  MECHANICAL ARRANGEMENTS FOR [OIII] FILTER
  =========================================
  
  Require rigidity with no vignetting.
  
  Prefer square hole or round but with extended corners.
  
  How many rays are vignetting with 182 mm diameter filter?
  
  How many rays are "not useful" in the case where the
  dispersion axis of the chip is 4k (instead of 2k)?
  
  Suggest that fabrication problem be left to NFRA if
  a square hole is required.
  
  Tilt option desirable (7 degrees, with beam displacement
  is not in dispersion direction)
  
  Discuss all this with RSAA.................................KCF
  
  
  [OIII] FILTER
  =============
  
  MA/RM point out lead time of 4 months (so order in January)
  
  Not enough money for full suite.
  
  Steep sides take preference over low ripple.
  
  Baseline is now 30A plateau (proably 45A FWHM), 
  with 1200 km/s redhshift
 
  Note that there is a shift of 2-3A (to blue) over the
  field, with respect to centre, which widens the nominal
  bandpass.
  
  MA has experience of 80% 27A wide filter from Barr
  
  Baseline filter for Virgo: Vsys 1200 km/s, 45A FWHM (this assumes
  plateau is 0.63 * FWHM.
  
  OPTICS PRODUCTION
  =================
  
  How do we specify and verify the optics, especially at
  RSAA where no testing is available.
  
  Talk to KT...............................................KCF
  
  DICHROIC
  ========
  
  3% loss and/or ripple (existing offer) is too much.
  
  Can we do better and how much would it be?...............ND
  
  Note: there was some discussion of reversing the dichroic direction to
  ease the problem. 
  
  GHOSTS
  ======
  
  ND reviewed the various ghosts, in particular
  
  1) coll (m=0, m=0) CCD  (two grating concave arm ghost)
  2) CCD (m=0) CCD	(one or two grating arm)
  
  which are serious and
  
  3) CCD dewar_window CCD
  
  and various other reflections which are not too serious if
  AR coatings are carefully watched.
  
  Changing to 600g/mm gratings eliminates (1) and (2) automatically but
  the new arrangement needs to be checked for possible new
  ones......................................................Gabe, Damien
  
  NEW GRATINGS
  ============
  
  It was agreed that the science is not compromised by the change to
  600g/mm gratings.
  
  ND claims the efficiency is higher. The design angle between
  the collimator and camera (AD=35 degrees) is close to optimum but
  a slight increase may be considered if needed. This would also
  possibly ease the space constraint on the filter.
  
  ND advocates the 1200g/mm for single-grating mode.  However in this case
  ghost (2) must be solved.  For this, a small tilt of the grating is
  enough.  In this case too, a small increase in AD might be useful. 
  
  Recompute ...................................................ND
  
  Price of gratings not on own substrate.......................MA
  
  MATRIX MASK
  ===========
  
  Tilted array, slit and slots, some aid in aligning columns of CCD with
  dispersion direction.  Holes to project onto minimum 3 pixels (for
  sampling)
  
  COMPARISON LAMPS
  ================

  Check on what is happening in focal plane area of instrument...KCF
  and at observatories...........................................KK/MA
  

  CCDs
  ====

  Check on availability of CCDs at observatories.................KK/MA

  COATINGS
  ========
  
  Best quoted seems to be 0.2% but some improvement would be welcome.
  
  Magda's tip: someone to contact Steve Vogt (Keck/Berkely Labs) 
  
  KCF recommends N2 flushing........talk to RSAA...............KCF
  
  Is flushing with N2 or dry air a possibility at site?........KK/MA
  
  BUDGET
  ======
  
  Problem areas filters/gratings and coatings.
  A budget for the Halpha camera is required: signs from
  OAC look positive. ESO and Kudritski to be approached.
  Bringing in a UK partner would also increase WHT access: Merrifield
  to be approached.
  
  

-- 
Nigel Douglas                           | Tel.  : (31)-50-3634088
Kapteyn Astronomical Institute          |  or   : 
University of Groningen                 | Fax   : (31)-50-3636100 
P.O. Box 800,  9700 AV Groningen        |
The Netherlands                         | E-mail: ndouglas@astro.rug.nl

http://www.astro.rug.nl/~ndouglas       | Home  : (31)-50-5418670