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MagIC Shutter Timing Accuracy

MagIC employs a leaf shutter. Tests performed on December 19, 2003 gave a timing error of 113 milliseconds at the center of an image for a 1-second exposure. The error is not constant over the field as seen in the shutter timing error image shown below.

 

shut.jpg


Shutter timing error image for MagIC. The timing error ranges from 113 milliseconds at the center to ~60 milliseconds at the edges for a 1-second exposure. The errors are in the sense that the shutter stays open longer than requested. The same shutter is used by each of the MagIC chips -- only the positioning of the shutter pattern on the image differs.

 

From these results, the following graph may be plotted of the ratio of the actual exposure time to the requested exposure time as a function of the requested exposure time. As may be seen, for exposure times greater than 10 seconds, the shutter timing is good to better than 1%. Images taken with exposure times less than 10 seconds can be corrected by creating correction images through observations of dome flats. The idea is to alternate 20-sec flats and twenty 1-sec flats. This is done multiple times to average out any variations in the quartz lamp intensity. Although it is best to take such data as part of the calibrations for your runs, a set of correction images (Quad-Amp unbinned and E2V unbinned) can be obtained by clicking here. These images are multiplicative. That is, if you have an image with a 4-sec exposure you would type in IRAF:

 

imarith image * 4sec image

 

shutter_timing.gif
Shutter precision for MagIC plotted in terms of the ratio of the actual to requested exposure time versus the requested exposure time in seconds.

 

 

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