PNS MANUAL: Filter Calibration

For each filter, and for each tilt at which it is used, it is important to perform a filter characterisation. The bandpass of the filter changes over the field, with temperature, and with aging of the filter. So the filter(s) should be calibrated often, and always if the tilt is changed.

This is done by using a tungsten lamp to determine the filter bandpass, in conjunction with the arc lamp exposures, which indicate the wavelength scale.

Where relevant (lamp, filter angle) !! UPDATE THE PNS HEADER CREATER GUI !!

How to take calibration exposures

Arc lamps

This is just an 800-second version of the usual procedure to increase the S/N, especially in the places where filter cutoff weakens the lines. Check that the images are not saturated.

Perform the following commands, in sequence:

  1. Issue AGCOMP command on A&G console (this puts mirror in calibration position). This can be slow; proceed meanwhile.
  2. Enter CALIB on PNS console (this puts in mask and opens shutter). Ignore the 1-second countdown.
  3. Once AGCOMP above has completed, on DAS console give arcslong command. This starts 800-sec integrations on both arms. Then follow the instructions the script gives, spiced with beeps:
  4. On A&G console do COMPLAMPS   CUAR+CUNE to switch on lamps.
  5. After 800 seconds you are asked to do COMPLAMPS   OFF to switch them off again.
  6. A little while later the readouts will start.

Continuum lamp

  2. CALIB
  3. COMPND 1 - put in neutral density filter to prevent saturation
  4. flats
  5. COMPLAMPS   W -- count to 12 seconds, then:
  7. finishpns
  8. COMPND   0.0

Measured Curves

Profile of Filter B measured with the PN.S in the centre of the field at two tilt angles in July/September 2001.

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