Date: Thu, 29 Oct 1998 07:35:52 -0700
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 981028
                        WEDNESDAY OCTOBER 28, 1998
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
   On the last night of the dark run, the weather cooperated.  It was clear
all night, with seeing varying between 1.0 and 1.5 arcseconds.
   When we opened, it was discovered that the 15V power supply of one of
the azimuth drive amplifiers was dead.  Power cycling the amplifier didn't
help.  A check of the fuses in the back showed none blown.
   To get set up on the equator the telesope was moved in azimuth using the
windscreen on manual.  Since we stayed parked there all night, the dead
amplifier had little impact on observing.
   While cleaning the drive surfaces this afternoon, I noticed the left
altitude encoder wheel was quite encrusted in moth guts.
   I took some measurements of the clearance of the west door over the
telescope when the altitude is in stow position ( 0.9 deg, or when the
windscreen plunger is just touching the stop ).  The low point, which is on
the south side of the west door, was 2.5 inches above the front end of the
windscreen.  On the north side of the west door, the clearance was around
4.5 inches.
   Once set up on the sky, the first task was to get the best images we
could.   Donuts showed a need for Y-tilt at the same settings which looked
good a few nights ago.  So I took the telescope to zenith and relaxed the
primary.  No change.  Next I homed the primary.  Images still look the same
afterwords.  Homing the secondary didn't change anything either.  French
mentioned that some work on pinning the Truss had been done during the day
which may have affected primary/secondary positioning.  We applied tilt to
the primary to get rid of coma.  The best values for this were...
        setmir  0       -11.3   55.7    1675    350
        galil   5350    -6750   2800    -5950   46200   46200
After looking at the camera array, and not being satisfied with image
quality away from the center, we decided to convert the tilts we applied
tonight to a translation of the primary.  We ended up at
        setmir  0       -1.3    5.7     305     80
        galil   4700    -3550   300     -10350  1050    1050
after implementing additional tilts.  This gave pretty good images across
the array, but favored the leading side of the array.
   A small change was applied to the linestart rate as well.  For the
science run ( #211 ) the rate was 26319.  This run went from about midnight
until 04:40 when the archiver stopped writing to tape and the queue depth
got too large.  This happened after we switched tapes, and may have had
something to do with archFldPause getting reset to a smaller number after
we had set it to an adequately large one, but it isn't clear yet.
   After a bit of thrashing around to recover and get going again, the last
part of the night was spent doing focus sweeps.
   The camera was taken off the telescope at the end of the night.  The
next night use of the telescope is scheduled to start the second week of
November.
                                   Dan