Date: Wed, 23 Sep 1998 03:25:47 -0600
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 980922
                        TUESDAY SEPTEMBER 22, 1998
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
   The enclosure was rolled off at 18:30.  The imager was briefly lowered
from the telescope and a shim was added.  The intent was to level the focal
plane across the array.  As well as could be determined in 2 to 3 arcsecond
seeing, this seems to have been achieved.
   As mentioned above, the weather tonight was poor.  Strong east winds
made for seeing in the 2 to 3 arcsecond range.  A nearby thunderstorm in
twilight forced us to close for about an hour and a half ( from about 20:00
to 21:30 ).  We reopened when the threat was gone and remained open in
mostly clear skies until about 01:00 when clouds moved back in.  It began
raining at about 02:00.  We did not reopen.
   During the time we were open, Robert did more work on the focus loop.
It managed to keep the telescope focused despite the poor seeing.
   We unfortunately had several problems with the telescope this evening.
First, the fiducial setting function apparently had incorrect positions, as
the fiducial positions were not the ones we determined at the start of the
run.
   Next we found that the scale factor was changed, so that even after we
entered the correct positions, we did not slew to the desired position.  We
went about 2.3% too far.
   The third thing we noticed was the telescope azimuth drives were causing
a noticeable vibration in the telescope when moving at all but the slowest
speeds ( <3000 cts/sec ).  It was also faintly audible as about a 20 to 30
Hz hum.  It happened in either direction.  We tried moving again after we
had reopened, and this time we could not make it hum.
                                    Dan