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S--Distortion Correction

The IPCS-II S-distortion correction is a rebinning operation performed by the DMS, and the parameters for the correction are determined by the DMS.

Set up the spectrograph and comparison lamp unit to give a narrow tungsten spectrum with reasonably uniform illumination along the spectrum:--

Open the shutter carefully in OVERSCAN mode to check the count rate, and adjust the comparison filters, slit width and grating angle if necessary.

The s-distortion correction must be calculated at full (x8) resolution in both X and Y directions, even if this resolution will not be used for the observations. Run the ICL procedure:--

IPCSSDC

which will set up a full resolution window 30 camera pixels wide centred on the spectrum. If, after running this procedure the tungsten spectrum is not in the centre of the window the value of the Y starting pixel of the CCD window must be changed, this can be done with:--

SEND IPCS OBEY Y_CCD_WIN MOVE <ystart> 30

The existing s-distortion correction must be turned off by typing at the DMS control window:--

0 ESD

At the ICL terminal take a fairly long exposure, it is important to have a strong signal in the S-curve:--

IPCSOPEN
EXPOSENP IPCS 1000

After this exposure has finished, close the IPCS shutter with:--

IPCSCLOSE

then at the DMS control window type:--

CALC-SDC

This calculates the s-distortion correction, and takes about 80 seconds during which time the DMS will not respond. After the correction has been calculated it must be loaded and enabled on the DMS control window with:--

LOAD-SDC
1 ESD

S-distortion corrections can be stored on the DMS disk with:--

PUT-SDC-ARRAY

and recalled with:--

GET-SDC-ARRAY

After recalling an s-distortion correction it is necessary to load and enable it as described above. Unlike the first generation IPCS on the INT the s-distortion correction is a digital process, and no ``tweaking'' is necessary or possible.



Previous: Camera Head Rotation
Up: Setting up the IPCS
Next: Collimator Focus
Previous Page: Camera Head Rotation
Next Page: Collimator Focus


Fri Jan 7 15:34:48 GMT 1994