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QUIRC User Guide
dither subtract on/off This option, when turned on, will subtract the previous image
from the current one and store the result in a file with a “chop" added to the normal
data file name instead of the file number. The name is the same as the chop mode
described above. This is often useful when dithering on a faint source that cannot
be seen without subtracting the sky/array background from the image.
For experienced users: note that if you want to use auto from a script, you can specify
the complete set of parameters, in the order above, as numeric arguments. Be careful not
to skip any, and use 1 for on and 0 for off.
clear num Clear (reset) array
clear resets the detector num times, default 1. If you have CTRL-C’d out of an
integration, you should do a clear to reset the device and qcdcom. If you do not use
clear after CTRL-C, on typing the next go qcdcom will assume you want to continue the
previous exposure.
comment text Adds a comment to the obs.log file, and to the FITS header of the
image file. This is added only to the next observation header, then it is cleared.
et seconds Set exposure time
et sets the exposure time. Any floating point value is accepted; the accuracy of the
exposure timing is somewhat better than 0.01 second, but it is ultimately limited by the
mechanics of the shutter. et uses Unix to compute the exposure time, and an exposure
which is based on Unix timing can be interrupted. Some care is taken to make sure that
the unix timed exposures are correct, but the machine running qcdcom is heavily loaded
it is possible for the shutter to stay open slightly longer. The exposure time recorded in
the header, however, will reflect the true amount of time the shutter was open.
filter num command Set filter
This command selects the filter setting. If no filter setting number is given, the list
of installed filters and the current setting is given. To specify a filter setting, its number
is given. If it is different than the current filter setting, the wheels are moved to the new
position. Note that for a filter wheel setting, both wheel positions are specified and the
movements are done simultaneously. See the fw command description below if other
filter wheel motions are required. To reinitialize the filter wheels, the command fi
home is used. One can use fi home1 or fi home2 to reinitialize only one particular
wheel. To use the polarizer (wheel 2 position 8) with one of the filters in wheel 1, one
adds the word “pol" after the number requested, e.g. fi 1 pol will select filter setting
1 and the polarizer instead of the OPEN position in wheel 2. Since the polarizer is in the
second wheel, it can only be used with filters that are in wheel #1 (filter settings 1-7).
The command fi DARK will move the filter 1/2 filter step backward between filters
to aid in taking a dark frame if necessary. Note that there is now a LOWFLUX filter
setting which should give a reasonable dark frame. The command fi BACK inverts the
DARK command and restores the wheel to its previous position. Be very careful to issue
BACK when finished taking dark frames, otherwise the filter wheel position will be lost.
If this happens, more than one DARK or BACK command in a row or not in pairs are
issued, or the filter wheel motion fails for any reason, issue a filter home command
to re-calibrate the filter wheel positions. It is well worth the extra time.