Date: Wed, 28 Apr 1999 05:42:50 -0600
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 990427 ( MJD 51296 )
                         TUESDAY APRIL 27, 1999
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
   Tonight was the productive engineering night we'd be trying to get for
the past two weeks.  The weather was gorgeous, the telescope behaved, and
we got a 1.4 arcsecond sky rms model for the 2.5m!!
   Jeff and Ellyne were here during the day and for the first few hours of
the night, and got the engineering camera mounted, as well as some practice
with the interlocks system.  I arrived around 22:30 and we got the
telescope balanced for the engineering camera with a cartridge, and one
spectrograph on the rotator.  The counterweight settings for this
configuration are 285 on each.
   Something changed with the alignment of the finderscope to the
engineering camera.  I suspect the scope may have got bumped.  It was
fairly quickly re-aligned with the engineering camera by slewing to Vega
and using the card trick to place it on the chip.
   Russell modified/debugged some new TCC code, which enabled us to run an
automated pointing model.  With the axes initialized before each slew, we
got excellent model data.  We got a 30 point model in roughly 2 hours, and
the fit was 1.4 arcseconds sky rms!!  This rivals the 3.5m's best results.
A couple stars were tried after the model was implemented, and they showed
up right on the center of the engineering camera chip within an arcsecond
or two.  I think this really shows the potential of the servo system.  It
might be nice to get a model with more data points, but if the current
pointing accuracy holds, I think we're there in terms of an operational
model.
   Twice after an AXIS INIT tonight, the telescope started moving in both
axes.  The rates were faster than normal tracking, but not as fast as
slewing.  In one case I stopped motion with a stop button, and the other by
hitting "s" in the Menu.  In neither case did the MCP crash, or even stop
sending updated axis position information.
                                  Dan
P.S.  No observing was done last night as mounting the spectrograph was a
two day project which didn't leave the telescope in an observable state
after the first day.