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Dome offsets and flat fields » History » Version 3

William Wester, 12/27/2013 11:14 AM

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h1. Dome offsets and flat fields
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Introduction: pre-March 2013 it was noticed that there could be small mis-alignments when the dome was moved into position
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for daily flat fields and/or DECal scans. A piece of safety tape was placed so that it would show proper alignment when
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the dome was moved into proper position. The telescope operator, as part of the procedures, now checks for this proper
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alignment. Indeed, some of the early daily flat fields (before the procedure) show a "rim" about 1/3 of a CCD wide
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with response lower by about a percent.
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It is difficult to diagnose whether the observation might be due to dome mis-alignment as the screen illumination comes from
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four discrete stations mounted on the outer ring and the screen itself is nearly a perfect Lambertian reflector (brightness
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is the same no matter the view onto the focal plane). This series of studies attempts to look at the effect of the dome flats
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versus small offsets in the dome position to see whether the illumination pattern matches some of the early problematic daily flats.
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"DocDB 7024":http://des-docdb.fnal.gov:8080/cgi-bin/ShowDocument?docid=7024 (Mar 2013 study)