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Concepts

Wed, 04/28/2010 — Daniel

Definitions

  • Lights - Frames that include the subject matter.
  • Offset/Bias frame - A calibration image taken with little to no exposure time.  Corrects for the noise inherent in the CCD.  Can be taken anytime and are considered viable for long periods of time.
  • Dark frame - A calibration image taken with the same exposure time as the "Lights" frames.  Corrects for thermal and electro-luminescent noise that accumulates over long exposures.  Should be taken near to the same time as the lights so that temperature conditions are nearly identical.
  • Flat frame - A calibration image taken of a uniformly bright, white screen.  Corrects for optical problems with the CCD and telescope.  Note that the focus point used on the subject must used when taking the flat frame.
  • Cosmetic file - A file specific to IRIS that identifies hot, or warm, pixels on the CCD.  Derived from the dark frame.

Hints

  • Take several (7-9) exposures of each of the calibration frames.  Then use IRIS to combine them.
  • 2:1- lights to darks

GUI Procedures for IRIS

  • Preprocessing->"Make an offset..." - Save the resulting master offset image.
  • Preprocessing->"Make a dark..." - Save the resulting master dark image.
  • Preprocessing->"Make a flat-field..." - Save the resulting master flat-field image.
  • Load the master dark image and run "find_hot cosm X".  Vary X until 100-200 hot pixels are identified.  Result is in cosm.lst.
  • Preprocessing->"Automatic preprocessing(1)..." or Preprocessing->"Automatic preprocessing(2)..."

CLI Procedures for IRIS

 

 

The above has been adapted from http://astro.ai-software.com/articles/dslr_iris/dslr_iris.html and http://www.saratogaskies.com/articles/cookbook/index.html