Date: Sun, 21 Mar 1999 05:54:40 -0700
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 990320 (MJD 51258)
                         SATURDAY MARCH 20, 1999
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
   It was a good night tonight.  Skies were clear by astronomical twilight
and remained that way all night.  Seeing was poor for the first half of the
night varying between 1.5 and 2.5 arcseconds.  However shortly after
midnight, the winds shifted from easterly to southerly and seeing improved
to between 1 and 1.5 arcseconds ( individual chips got as low as .8 ).  The
southern equatorial strip was imaged ( run 752 ) from about 22:00 until
05:00.
   The enclosure was rolled off at around 18:00 after being closed all day.
The exhaust fan was turned on at about 16:00.  Images at the start of the
night had none of the nasty astigmatism seen first half of last night.  As
the optics were in the same position as last night, the only apparent
change was the telescope not seeing the sun in the afternoon.  This would
seem to indicate some thermal effect which is quite long lived when the
telescope is out during the day, as images last night were still quite
astigmatic six hours after sunset.
   The focus loop worked well all night, with no communications problems or
oscillations.  There was one event at around frame 50 of run 752 where the
estimated focus value of CCD60 jumped by around 100 microns, then a few
frames later swung to the other side of focus by 50 microns.  Fortunately
this had only a small effect on the piston of the secondary as it was a
relatively brief transient.  The absolute piston of the secondary varied
from around 1600 at the start of the night to about 1450 by night's end.
                                Mirror Numbers
  Primary numbers:
   setmir:  0 -25.8  17.2  939  1409
   galil:   6300 -3850 150 9700 24750 24100
   linear guages:  1:+01.9270
                   2:+00.5610
                   3:+00.5570
                   4:+00.3565
                   5:+01.9285
                   6:+00.4290
   Secondary numbers:
   setmir:  1500*  -255   0   0 133
    galil:  1750167   1830167    2098938   -9642  -16642
       *The piston was taken over by the focus loop and did not remain here.
   The enlosure was closed at about 05:30.
                                   Dan