MDM Observatory 1.3m Telescope Observer's Report for 2008 Sep 26

Observer(s): Atlee
Institution(s): OSU

Instrument: 4k Camera

Worked for 8 hours (most of the night)
Conditions were Non-Photometric most of the night.
No equipment or software problems were encountered.

Seeing and Weather:
   Clouds from 1800 until 1900.
   Beg: Patchy Clouds, Winds Moderate
   Mid: Clear, Winds Light & Variable
   End: Clear, Winds Light & Variable

Observing Summary:

I conducted an ad hoc campaign to study the variation in focus
as the telescope tracks across the sky.  I set the focus as best
as I could at a variety of declinations and hour angles and
then allowed the focus to drift naturally.  

In the first field, I found a new problem.  The focus position
does not appear to be repeatable.  Focus positions which gave
reasonably good PSFs during the focusing did not yield good 
PSFs in the images taken subsequently.  After my focusing
exposures, I moved the telescope to ~15mm below the nominal
focus position before moving up to the desired value, in
keeping with my experience last night that the nominal focus
values must be approached from below.  The focus in the later
images, which were taken near the declination of the
observatory, appeared to be stable, however.

I was forced to do a partial lightning shutdown to return the
DAQ to a known configuration.  (See Trouble Report.)  It appears
that the TCS box is on UPS Breaker #2 not Breaker #3 as
previously indicated.  This may be problematic as most of the
DAQ computers are also on that breaker.

It appears that the focus of the telescope CAN be stable.  In
fact, the focus of the telescope only ran away during one test
sequence.  However, it is not easy to get the telescope into a
repeatable focus position, either from above or below, to get
a good PSF.  Focus values that yielded nice, round PSFs during
the focus image yielded elliptical or even irregular PSFs
shortly after when the focus was set to the nominal values for
the test sequence.

On several occasions, the high pitched whining from the Dec
motor seems to be associated with changes in focus.  That is,
once the  forcible adjustment  of the telescope to stop the
whine also stops the change in focus.  I have no idea how that's
possible, but it happened more than once.

In summary: in many cases, the focus was quite stable
throughout the sequence.  In others the quality of the focus
declined so quickly that it was impossible to get the telescope
in focus in the first place.  Finally, in the last sequence I
did I found that the focus would remain stable for long periods
before slipping stochastically.  In one such case, it even 
slipped back into better focus.

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Submitted on 2008 Sep 27 [4:07:30]