MPIA Students' Homepage

General information

• Contact person: Markus Feldt
• Also have a look at the homepage for further information not contained in the "complete" manual!

Practical notes

Background knowledge

• Purposes of wavefront analysis in astronomy
• Generating a plane wavefront:
  • Laser produces parallel light
  • But this is coupled into the fibre using a lens
  • So we need a collimator
• CCDs:
  • physical background:
    • Photoelectric effect
    • Process of reading the CCD
    • Amplifying the signal
    • Analog/digital (A/D) unit, produces 12-bit output -> finite resolution of electrons
    • Efficiency (electrons/photon)
  • Quantities and effects:
    • Bias
    • Flat-field variation
    • Dark current

Technical aspects

• Don't try to follow the manual word by word, especially
• Working directory on PC: /home/fprakt/INDIVIDUAL_DIR
• Flat-field LED: keep voltage <= 3.3V!
• Representation of an image on screen:
  • This TFT screen displays 24-bit colors
  • As grey tones are made of equal values of R/G/B, it can distinguish only 8-bit (i.e. 256) shades of grey
  • But the camera delivers a 12-bit image
  • This is why we need to adjust the color scale when displaying an image
• Usage of objectives:
  • If you use the big objective, you can fix it to the rail with the left screw and still make fine adjustments using the micrometer screw
  • Remove the objective before taking flat-fields (otherwise, not the entire CCD will be illuminated; even though in this way, you cannot correct for potential intensity variations due to the objective)

Hints for viewing FITS files

• From shell: ds9:
  • view -> tile
  • Color maps:
    • Adjusting the scale: hold down right mouse button and drag up/down or left/right
    • Try different scale modes
    • Try color button
    • Resetting: color -> reset color map