Hardware Overview
The Direct Imaging Camera sits at the f/17 cassegrain focus of the Nickel 1-m telescope. The camera is optically very simple, consisting of an aperture wheel, filter wheel, and shutter, contained in an assembly in front of the focal-plane CCD, lying behind a fused-silica window in a liquid nitrogen dewar.The current CCD (CCD-2) is a thinned, Loral 2048x2048 array. The field of view is approximately 6.3 x 6.3 arcminutes with a pixel scale of 0.184 arcsec/pixel. N.B. It is the observer's responsibility to fill the CCD dewar with liquid nitrogen twice in each 24-hours: once before observations begin in the evening and again when observations end in the morning. The aperture wheel is generally placed in the open position for direct imaging, except when using one of the occulting disks provided in the wheel. The aperture wheel is remotely controlled from the Nickel Motor Control GUI. The filter wheel, located just below the aperture wheel, has five positions. Filterwheel position 0 is always empty. Up to four 2x2-inch filters can be loaded into the remaining positions. The filter wheel is remotely controlled using the Nickel Motor Control GUI. The shutter is mounted just below the filter and aperture wheels. There is no minimum exposure time for shutter operation, but shutter timing errors are a few milliseconds. The timing error on a 2-second exposure should be less than 1%, but such short exposures are nevertheless not recommended for absolute photometry where high accuracy is critical. The shutter is of the diaphragm type, so that errors due to underexposure at the edges of the detector compared to its center, become very significant for exposures of less than 0.5 seconds. The CCD is in vacuum, behind a fused-silica window. While we try our best to keep the front surface of the window as clean and free of dust as possible, some dust is unavoidable. Dust motes on the window will be apparent in flat-field exposures as donut-shaped areas of slightly reduced sensitivity. Because the window is well protected, the dust pattern tends to remain fixed in the course of a run, and can be largely accounted for by flat-fielding. |
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Nickel Direct Imaging Camera, Filter and Aperture Wheels |
Support Astronomer (sa@ucolick.org) Last modified: Tue Jul 17 18:12:07 PDT 2012