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 a filter wheel and shutter contained in an assembly in front of the focal-plane CCD.The current CCD is an Andor iKon-L 2048x2048 array. The field of view is 5.68 x 5.68 arcminutes with a pixel scale of 0.1665 arcsec/pixel (13.5 um pixels).The CCD is normally operated at -80 degrees C, using a thermo-electric cooler and water chiller, to reduce dark current to 3.48e-5 e-/pixel/sec. The filter wheel, located just above the camera shutter, 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 Filter Control GUI. The shutter is mounted just below the filter wheel. 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. For photometry and flat fields, a minimum exposure time of 3 seconds is recommended. 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 and Filter Wheel |
Support Astronomer (sa@ucolick.org) Last modified: Mon Nov 2 14:51:48 PST 2026