MDM Trouble Report for 2014 Jun 21

Telescope: 2.4m
Observer(s): John Thorstensen (Dartmouth)
Instrument: Modspec + echelle

Problem(s) Encountered:
As twilight approached I set up a sequence of 10-minute exposures
on an object.  The first 3 were fine, the fourth was a bit weak,
and the last two were completely blank -- the chip read fine, and
there were cosmic rays on the images, but there was no light.

I thought (of course) that the shutter had failed, so I closed
up and pulled the shutter from the instrument.  It worked 
when commanded from the Uniblitz box; it worked when commanded
from the non-intuitive shutter control icon in Owl.  I then
put it back into the instrument (after re-seating that 
unfortunate O-ring - hope I got it right) and took a few short
Neon exposures - and it worked again.  

So I don't know what happened.  I can't think of anything else
that would do this except a failing shutter, but it seems
to check out OK.  Maybe it's on its last legs, and taking it
out of the instrument cured it temporarily?  

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Submitted on 2014 Jun 22 [4:57:56]