Date: Wed, 7 Apr 1999 02:52:08 -0600
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m obslog 990406 ( MJD 51275 )
                          TUESDAY APRIL 6, 1999
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
   Tonight didn't go a lot better than last night.  Russell and I still
couldn't slew using the TCC.  Either the MCP would crash, or one or more
axes would go into oscillation, or both.
   The azimuth fiducial gave a position which was 15 degrees off in the
positive direction.  Charlie Briegel later fixed this problem.  There was
an off-by-one error in which fiducial was being chosen as the valid one.
   When the altitude fiducial was used to set position, the equator mark
was some 13 arcminutes off, when I moved to 57:13:11 ( put another way, to
get the mark to line up I needed to move the telescope to 57:00:00 ).  If I
remeber correctly, this position was much more accurate than that during
the last dark run.  A check of refraction at 57 deg, showed a difference of
less than 30 arcseconds, so I don't think that is it.
   We were open from about 19:30, when the wind died down enough, to 21:30,
when dust counts shot up.  After that dust count remained high and after
about 01:00 thick clouds moved in.
   Charlie came back in around 22:00 and worked with the rotator inside the
building until about 02:00 ( thanks Charlie for the extra time and effort
).  Progress was made regarding MCP crashes when commanding moves with the
TCC.  Humming of the rotator during moves, and occasional unexpected
oscillation were still occuring though.
   It seems that quite a bit more work on the MCP, servos, and fiducials is
needed before a pointing model can be acquired.
                                  Dan