6.4 How to Recalibrate

To recalibrate using calfoc, first assemble your set of calibration reference files. You can then use the task chcalpar in the stsdas.hst_calib.ctools package to edit the header parameters in your .d0h file so that they point to the desired calibration files. After you have set these parameters, run the calfoc task, and it will produce recalibrated FOC data files.

If you would rather execute the individual steps using the appropriate IRAF tasks, these are the steps to apply:

• Dezooming: Use stsdas.hst_calib.foc.focphot.dezoomx. This step is straightforward.
• Absolute sensitivity keywords: Use stsdas.hst_calib.synphot.bandpar as described in "Absolute Sensitivity Keywords" on page 6-8 or stsdas.hst_calib.synphot.calcphot as described on page 3-16.
• Geometric correction: Use stsdas.hst_calib.foc.focgeom.newgeom. Again, this step is relatively straightforward.
• Flatfielding: Use iraf.images.imarith. Remember to use the appropriate subset of the full-format flatfield and to multiply the data by the reference file, unless of course the flatfield has been derived by the user and is not inverted. For a 512 x 512 normal format image the appropriate IRAF command might be:

        fo> imarith image.c0h * flatfield.hhh[257:768,257:768] \ 

        >>>   image.c1h