Quote:
Originally Posted by strongmanmike
Oh and Jase I'm not sure where those halo like rings are coming from? They may be the CCD window or the KAI11002 cover slip..? But I need a good clear night to really get to the bottom of them. Like you say they don't bother me that much and may just be something I have to live with like reflector imagers put up with diffraction spikes..?
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Possibly Mike. Though the CCD will have a MAR (multi-layer anti-reflective) cover glass, then above the chip is the cover slip which also has an anti-reflective coating. However, it doesn’t always stop internal reflections. If your Ha filter has a matt and reflective side, I would recommend pointing the reflective side towards the telescope (dull side to the chip). You probably already know all this.
If you really want to know where the halos are coming from, you need to measure the diameter of the halo and know the mechanical measurements of the CCD. In particular distance between the CCD chip and MAR, MAR thickness, MAR to cover slip, cover slip thickness, distance from cover slip to filter and then finally filter thickness. Other than the halo diameter, the above are not used in the formula – you just reference them once you’ve obtained result X.
HD = Halo Diameter in pixels
P = Pixel size in microns
FR = Focal Ratio
(HD * P * FR) / 2 = a distance of X mm from the chip.
Having stated all this, I usually image process them out. I seriously think yours are thin high-level cloud rather than reflections. They are rather small. More tests will prove this.