MDM Trouble Report for 2016 May 09

Telescope: 2.4m
Observer(s): Zhijie Qu (University of Michigan)
Instrument: OSMOS

Problem(s) Encountered:
Actually, what's the wrong during the observation, but the obtained images are really strange.
In many images or imaging flat field, there is a dark region, which I don't know the reason.
Also, the seeing is good, but there is always strange tails around bright stars in Halpha band.

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Submitted on 2016 May 10 [4:31:39]