Date: Mon, 12 Apr 1999 04:36:22 -0600
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 990411 ( MJD 51280 )
                           SUNDAY APRIL 11, 1999
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
   Tonight was a good night.  In short, I think we are ready to take
pointing model data!
   I started by testing that I could take engineering camera images with
the TCC.  This was successful once I realized the camera ID was 2, which I
found by setting the instrument to ENGCAM.
   To insure a good starting point, I homed both mirrors.  The secondary
had measurable position error but I'm not sure how large it really was.
The line was
    000030002,  000010002,  000010002, -000000350, -000000200 position error
   The primary had some really large number for target position of axis A.
The field was all nines.  I couldn't get rid of this by a MOVE, or even
HOME.  I ended up power cycling the primary galil.
   Once open, I slewed the telescope to Polaris, and Connie helped me align
the finderscope to the engineering camera chip.  The finderscope and EC are
well aligned at this point.  I would ask anyone doing work around the 2.5m
telescope not to bump or even touch the finderscope.  It takes quite a
while to do this alignment.
   With the finderscope aligned, we slewed to an FK5 star and used the
finderscope to quickly get the 5th magnitude star on the chip.  The
required exposure times to avoid saturation were too short to even out the
seeing, so we will want to put in an ND1 to ND2 filter when taking the
model data.  The centroiding algorithm and offset to the center worked
reasonably well, though the star after the correction wasn't quite at the
center.  It showed up about 50 pixels low, and 10 pixels to the left.
Repeated TRACK/PTERRs didn't walk it off the chip or bring it closer to the
center.
   We are essentially ready to try a model at this point!
   There were a few axis problems tonight which should be mentioned.  The
rotator went into oscillation part way through a slew, hummed for a minute
around -25 degrees, then quited down and finished the slew with no hum.
   A large calibration offset ( around half a degree ), caused the altitude
to stop tracking.  While this might not be unexpected, the fact that it
could not be recovered using AXIS INIT cause problems.  Even after issuing
an AXIS STOP from the TCC, when I attempted to enter the Menu program to
reset, stop, and hold altitude it crashed.  I couldn't bring it back to
life with ctrl-x, and so had to reboot via the reset button.
  A couple of times AXIS STOP caused an axis to drop out of closed loop,
and required going into the Menu to stop and hold again.
  On a couple of other occasions, an axis ( alt and rot to be specific )
seemed to be tracking, but well offset from the TCC requested position.  It
seems likely that it was acting on an old MOVE, and ignoring the current
ones, so it looked like it was tracking with an offset.  As above, the only
way to get things talking again was to go to the Menu and reset, stop, hold
the axis and then try again with the TCC.  AXIS INIT was insufficient to
clear the problem.
   The telescope was closed at about 03:30, once we had tested the pointing
model commands and the finder scope was aligned.  We had been pushing the
dust limit for some time and since we had accomplished what we had intended
to do for the night we decided to close.
                                   Dan