MDM Observatory 2.4m Telescope Observing Report for 2016 Mar 15

Observer(s): Frank
Institution(s): OSU

Instrument: OSMOS

Worked for 12 hours (all night)
Conditions were Non-Photometric most of the night.
No equipment or software problems were encountered.

Seeing and Weather:
   Beg: Seeing 1.5 arcsec, Cirrus, Winds Light & Variable
   Mid: Seeing 1.2 arcsec, Cirrus, Winds Light & Variable
   End: Seeing 1.2 arcsec, Clear, Winds Calm

Observing Summary:

Another almost(*) perfect night.
Good conditions.

Just one word on the pointing and/or tracking : during one longer exposure,
I noticed that the counts in the spectrum were much lower than expected.
A quick position check revealed that the source had moved by about 400 pixels
(=130 ) out of the position in the slit it had occupied before --- without the
guider somehow noticing (?). When I then checked the position of a bright
star in a 10s exposure, there was a drift visible as if the tracking had
stopped working (although the switch on the TCS was definitely not in off
position). I restored pointing via the zenith-method -- but in the a subsequent
test of slewing in all 4 different directions, an E or W slew resulted in very large
displacement (up to 1200 pixels in one case !). Hence, I repeated the zenith-method, and 
after that second repair mission, the pointing worked more reliable -- 
although there remained a somewhat annoying offset even after that from time to time.
These offsets occurred most prominently when moving from far E to far W 
(but interestingly not in the reverse direction). 
For OSMOS with its big field of view, this behaviour is mostly an annoyance,
but could prove fatal for instruments with smaller FOV, I suppose.
After that incident and the  fixes , the offset were around +-250 pixels, mostly in E/W
rather than N/S.

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Submitted on 2016 Mar 16 [7:02:59]