Horizontal Heavens Observatory "...From  A Galaxy Far, Far Away"
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This page was last updated on 10/08/14.


FOR SALE 10in Meade LX200 EMC

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05/09/2014 Storm Damage


Flat Fielding, OR Ghosts & Gremlins Exposed

Below is a flat field image taken with my ST-10XME w/H-alpha and OIII filters on my 10" LX200R at a 3 o'clock position.  This image has been stretched to the maximum in order to show the many artifacts that are inherent with CCD flat field images.  This is why we need to process with flats. 

CLICK on the image for full resolution and looking closely you can see:

  • The actual pixel grid layout
  • Optical vignetting, or at the very least Cos4 illumination drop off on the left side (probably due to CCD/reducer mis-alignment)
  • Large dust mote in upper center
  • Smaller dust motes (small donuts)
  • Hot pixels in the flat field that need to be dark-subtracted before being used in processing
  • Diagonal "moir banding" that is quite possibly a result of the misregistration of the microlensing over the pixel grid.  Also note that this banding is opposite between the Ha and the OIII flats.  In other words, bands that are bright in Ha are dark in the OIII flats.  Look closely at the very tip of the bottom right corners of both images to see this effect.
  • Mottling possibly due to variations in the filter glass, cover slip, filter wheel window.  Sometimes this shows up as a color/filter specific gradient in a final image.