Date: Tue, 8 Jun 1999 06:00:51 -0600
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 990607 ( MJD 51338 )
                           MONDAY JUNE 7, 1999
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
    Observering team:   Dan Long                (APO)
                        Francisco Castander     (UC)
                        Aronne Merrelli         (CMU)
                        Matt Newcomb            (CMU)
   Since the DA hardware was not repaired to the point of supporting an
imaging run, the spectrograph was used tonight ( rotten seeing would have
made it a spectroscopy night in any case ).  Despite a weather delay, we
got some guiding tests, and even one Coma exposure.  More centroiding
problems prevented the TCC guider from working.  However "evil" guider
worked well in a 45 minute run, and is fast to setup as well.
   The imager was on the telescope during the day being pumped down.  That
was finished around 20:30, and a test of the cooling system followed.  At a
little after 21:00 we took the camera off and put the corrector in, and
mounted cartridge 133, the Coma plate.
   Unfortunately as soon as we made the instrument change, we had to close
due to dust and high humidity.  This was around 22:15.  We remained closed
until 00:15.  I opened up and finished getting the telescope ready (
balance check and fiducial setting ).
        Fiducial readings:             Counterweight readings:  355
        Az:  120:45:44.939
        Alt:  14:53:08.887
        Rot:   0:59:55:35
It should be noted that it took two tries to get the altitude fiducial to
fire moving up ( it triggered every time moving down ), and that the
rotator fiducial wouldn't fire going either direction for three tries.  The
rotator fiducials on either side worked ( something like -3 and +5 deg ),
but of course they weren't valid fiducials.
   We then slewed to the coma cluster and centered up.
        Plate 133:  194.85, 27.95
   We were pretty low by the time things were set up.  The starting
elevation was around 35 deg.  By the time we were ready to guide it was
below 30.  We tried a few times to get the TCC guider to work, but even
after finding most of the stars in the setup phase of guiding, it would
quickly "lose" stars which were visibly still well centered in the fibers,
complaining about being unable to centroid.
   It was decided to see what "evil" guider could do.  We ran this guider
code which simply requires moving the telescope small amounts in a pattern
of object offsets, then determine which directions match which fibers, and
finally uses object offsets and rotation offsets to keep the stars
centered.  On the coma plate the only attempt made with this code resulted
in the stars walking away in rotation.
   During all this, Francisco took a single spectroscopic exposure in which
several of the larger brighter targets showed up nicely despite all the
fiddling with guiding.
   By a little after 02:00, the Coma field was too low to track any more (
rapidly approaching 20 deg ), so we changed to the FASTT field "L".  As
this one already had an instrument block generated, we saw this as our only
hope to get any further guiding tests.  There was a small delay during the
cartridge swap ( only a few minutes out of about a half hour operation).
It took a bit to figure out that the spectrograph slithead door had moved
just enough to make the slithead catch on the way down.  By the time the
cartridge was swapped, and were were on our target, it too was getting low
in the west.  We started tracking when it was at an elevation of 36 deg.
Fortunately some stars showed up on the initial pointing and not too much
tweaking was needed to get them all in.
       Calib offsets  .0008, -.003, -.10        Best focus -300
   This time we went with "evil" guider on the first try, but a variant
which applied rotation corrections of opposite sign.  This worked very
well.  It pulled all the stars into the centers of their fibers and kept
them there for about 45 minutes.  This code seems an excellent ( and simple
) interim measure to facilitate guiding until the centroiding issue can be
addressed in the TCC guider.
   It was interesting to note that towards the end refraction became
obvious ( below about 30 deg ) as the fibers near the edges of the plate
which were nearest and furthest from the horizon began to move toward the
middle , but guiding continued to work well.  We stopped guiding only 22
deg above the horizon.  At this point it was 04:10, so the telescope was
put away for the night.
   When I closed I topped off the 10 liter dewar for the spectrographs, so
it should make it until afternoon sometime before needing a fill.
                                MIRROR NUMBERS
   Primary:
   setmir:  0   3.9   -2.3   -128.1   -213.5
   galil:   4350 -1750   0 -16300  -11550  -11450
   linear gauges
        1.9330
        0.5545
        0.5565
        0.4225
        1.8835
        0.3840
   Secondary:  18.5 deg El.  Spectro as instrument
      SecOrient= 3642.7, -247.7, -100.0, -50.0, 378.9
      galil:  4622648.,4363588.,4780316.,-29042.,-34768
                                WEATHER
   Weather tonight was clear all night.  Winds were southwesterly at 10 to
20 MPH until about 21:00, then switched to the east at 20 to 30 MPH for
most of the rest of the night. temperatures were 12 to 14 C, the dewpoint
depression was 20C until the wind changed direction and ranged between 3
and 9 C the rest of the night.  Dust counts ranged from 2000 to about 3800,
and were over the limit between 22:15 and 00:15.  Seeing was miserable
until after 01:00 ( 3 to 5 arcsec ), but settled down to the 1.5 arcsecond
range for the last few hours of the night.
                                  Dan