Date: Tue, 22 Sep 1998 06:58:56 -0600 (MDT)
From: Russet McMillan
Subject: 2.5m obslog 980919
I don't believe this ever went through on Sunday morning, so I'm re-sending.
                         SATURDAY SEPTEMBER 19, 1998
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
We opened around 19:00 to partly cloudy weather.  We moved the
telescope first to the zenith to relax the transverse mirror supports,
then pointed a few arcminutes north of the equator on the meridian, on
the same strip observed the previous night.  During the azimuth
motion, we observed more of the resonant "bouncing" effect on the
floor as seen before.  Fortunately, at the highest permitted speed the
bouncing was minimal.  French Leger speculated that the resonance
might be due to the motion of the hanging racks.
Seeing was poor throughout the night (3.5m reported 1.5 - 2
arcseconds), and clouds ranged from uniform-thin to patchy-thick.
However, the humidity remained low and there was no danger of
precipitation.  Because of the uninspiring weather, the time was used
mostly for focus and image tests.
We started with the primary and secondary mirrors in essentially the
same positions as last night, adjusting only the secondary focus
(piston) position.  Pretty donuts on either side of focus indicated
that there was negligible coma, as seen on the previous night.  During
the first two-thirds of the night, Robert Lupton worked at closing the
loop on the automated focus routine.  After 02:30 we centered the
primary, taking care to relax the transverse supports by moving the
piston up (-1000) and then down to 0 again.  We tried different tilts
to find the best images without translating the mirrors, and found
that a tilt of 15 arcseconds in x and 60 arcseconds in y worked well;
thus the primary was at 0 15 60 0 0 in setmir terminology.  We then
re-centered the primary (relaxing the transverse supports once more)
and left it centered in preparation for some measurements to be made
during the day.
At 03:00 the camera was allowed to begin warming in preparation for
pumping procedures the following day.  We moved the telescope to the
stow position and rolled the enclosure back on at 03:30.
As reported by Dan Long for the previous night, we experienced one
difficulty with altitude motions at the beginning of the night when
something tripped as if a stop button had been pushed (which none
were).  This was easily fixed by pressing the reset button on the
amplifiers, but the reason for the trip in the first place is unclear.
We also managed to get the MCP into a strange state where it refused
to recognize the command "logout" -- it displayed the message "value =
0 = 0x0" and ignored the command.  Since only one MCP session could
run at a time, and we didn't want to risk losing the fiducial
positions if we disconnected the telnet session, we stowed the
telescope with one person controlling the move from the control room
and another monitoring the move (and counterbalancing the full 10l
dewars) at the telescope.
					Russet McMillan.