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ProEM is a 1024x1024 frame transfer camera with 13 micron pixels and optional electron multiplication readout, although we have never used that feature except on the commissioning run to observe the Crab pulsar. The camera is triggered by a GPS-disciplined double-quartz oven clock. The setup used most often is 4x4 binning for an effective pixel size of about 1/3 arcsecond. At the Cassegrain focus - currently the only available configuration - the plate scale of 7.3 arcsec/pixel yields an image about 1.5 arcminutes on a side.
Two filter sets are available. A manually-controlled wheel contains the Johnson-Bessel filters UBVRI, and an automated FLI wheel contains the standard Sloan filters and BG40. Most observers using UBVRI substitute a clear near-red blocking filter for U. When using the FLI wheel, this filter is removed.
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