Horizontal Heavens Observatory "...From  A Galaxy Far, Far Away"
Clear Sky Chart  

This page was last updated on 08/23/13.

Home

About  Horizontal Mike

Horizontal Hell

Planetary Nebula Discovery

Equipment

Observatory

Clear Dark Sky Charts

Local Links

Analysis Page

The Woodshop

Wood Working Links

Old Navy Pics 1974

 

GALLERIES

NEWEST Images

Comets ISS Shuttle Flyovers etc

Clusters

Galaxies

Moon Images

Nebula

Eclipsing Infrared Binary

Yerkes Observatory

Texas Weather

Birds & Critters

M42 Orion Nebula

NGC2024

NGC2261 + NGC2264 Nebula

 

TECHNICAL INFORMATION

MoonLite Focuser

Photometrics Cooler

Flocking LX200R

LiteBox for Flats

CCD Inspector Page

DEC Motor Modifications

Dovetail Mounting Details

Focal Reducer Information

LXD55 Mount Mods

Meade Superwedge Modifications

Robo-Focus

 

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.