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Focusing StanCam - a quick help

One should use the stancam.focus-script which finds a proper focus field, selects R-filter, takes and analyses the data and set the new StanCam focus value
  1. tcs.setup-tel-stancam (if not already done)
  2. stancam.focus

In case you want to change the "Telescope focus step size" use the switch "-s" e.g.

stancam.focus -s 75
Scroll this page to find the documentation of the focus-command

Focusing StanCam - the old, manual, way

In case you want to take and analyse a focus sequence "manually" follow these guide lines:
  1. Stop auto-guiding
  2. Start a focus sequence with the command: focusexpose (focus start-value) (focus step-size) (exptime)
    A good first guess is focusexpose 26130 100 15
    The image should look like this:

  3. Use the sequencer script focus-auto focus-step-size [image] to analyse the image.
    E.g. focus-auto 100

  4. Set the telescope focus e.g. tcs.focus-position 26330

    or on the TCS by (e.g.)"foc-pos 26330".

    !!!NOTE the smallest meaningful focus offset is about 20-30 TCS focus units.

  5. You can also use the Postprocess Imexam to measure the FWHM of the images (use a-key), quite imexam by typing q-key
    Take another focus sequence with finer focus step size if needed.

    If you have problems with the BIAS/imexam you can use iraf/imexam at florence.

    • in florence xterm window type xgterm &
    • in xgterm window type ecl and ds9 &
    • display saved stancam image displ /data/stancam/STnnmmxxxxx[1] 1 fi+ where nnmmxxxxx stands for the prefix and the number of the image
      (see the testimage " /data/stancam/EXfocus.fits")
    • type imexam and move the cursor on top of the star and press r for radial profile and/or a or , for aperture photometry
    • quit imexam by pressing q
    Note, that the telescope focus vs FWHM curve is rather broad around the optimum focus.

Back to top Last modified: April 19 2023