Sigma QUick Infrared Camera manual Cold Restart, Running VF to display data, Taking Dark Frames

October 30, 1997 9

5.2Taking Dark Frames

Since there is no blank position in the filter wheel and the shutter is warm, some extra care is required to obtain reasonable dark frames. With the installation of the second filter wheel, a “LOWFLUX" setting has been provided. This setting selects two filters simultaneously with incompatable bandpasses, e.g., the J filter and Br￿(2.16 ￿m). This produces a reasonably low flux condition at the array, limited by the out-of-band blocking of the filters and leakage around the filter wheels.

Another way to get a dark frame is to move halfway between filters on the wheel to block most of the emission of the warm shutter. Special commands have been provided for doing darks, and a typical sequence might be as follows:

>filter 2

>filter DARK

>dark 180 Dark Frame

>go 5

>filter BACK

This takes 5 180-second dark frames. The dark command works exactly like the object command, except that the shutter will not open for the exposure. Note you must use the object command before your next data exposure, or change the default actions with auto, or the shutter will not open! Also note that you should always do only one filter DARK followed by exactly one filter BACK, always in pairs, otherwise the filter wheel will get lost and require a filter home. Be careful, there is no indication from the program when this has happened, as there is no encoder on the filter wheel. Moving the filter wheel between the J and H filters, as in the example, appears to minimize the thermal radiation from the warm shutter reaching the detector.

6 Cold Restart

If the power should fail or the DSP computer should need to be reset, the following sequence of commands should be issued:

>sy

>df quirc

>du util

If this happened during a filter wheel move or pupil mask motion, you will need to reset that with the filter home or pupil home commands, respectively. Note that the pupil mask re-initialization can take a long time (up to 30 minutes!) and is a bit tricky. Because of this, observers should never move the pupil mask unless you are sure it is absolutely necessary–it usually isn’t.

7 Running VF to display data

The VF program is a tool for displaying FITS files, written by Tony Denault for the IRTF. See the VF manual for detailed information on the program and its capabilities. Its interaction with the qcdcom