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Help with diffraction-like spikes - blue channel only [Deep Sky] Processing techniques · David Ebbecke · ... · 7 · 217 · 4

deebbecke 0.00
David Ebbecke
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After stacking in WBPP (HaRGB), I observe an anomaly in the blue channel only, which appears only in the most prominent stars in Orion.  Initially, I let it go, but after combining channels, some further processing, and pulling the stars, I discovered what are now purple spikes.  Could anyone help me identify both the cause and a solution?  I'm providing an image of the master red (second image) to show that this did not occur.  The green and Ha masters turned out fine as well.

I'm using a WO Redcat 51 III, 2" Antlia filters, 2600mm PRO camera.

Thank you.
David 

Screenshot 2025-05-27 210637.pngScreenshot 2025-05-27 210655.pngScreenshot 2025-05-27 210717.pngScreenshot 2025-05-27 210800.png
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Overcast_Observatory 19.90
Chris White- Overcast Observatory
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Spikes are caused by something protruding into the light path. Do you have an oag in the system?  Is there any debris on the lens?  Etc…
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messierman3000 7.22
Oscar
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hairs on the blue filter? scratches maybe?

was there branches in the way, when you switched to the blue filter? if your imaging sequence was something like RGBRGB, then it cannot be branches, and it could be hairs on the filter.

Just using my imagination here. My 2 cents.
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deebbecke 0.00
David Ebbecke
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Chris White- Overcast Observatory:
Spikes are caused by something protruding into the light path. Do you have an oag in the system?  Is there any debris on the lens?  Etc...

Thanks for the reply, Chris!  I am using an OAG in the system.  It wasn't long ago that I cleaned the filters, so I don't suspect debris.  However, I will give it another inspection.
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deebbecke 0.00
David Ebbecke
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Oscar:
hairs on the blue filter? scratches maybe?

was there branches in the way, when you switched to the blue filter? if your imaging sequence was something like RGBRGB, then it cannot be branches, and it could be hairs on the filter.

Just using my imagination here. My 2 cents.

Thanks for the reply, Oscar.  I don't suspect scratches/debris on the filter, but the target was near the tree line, so this might be a possibility.  I didn't shoot RGBRGB, so an obstruction might be the culprit.  I shot this target over many nights and at various angles.  I'll go back this evening and have a look at blue subs from another night (provided others were taken) and compare.
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ONikkinen 4.79
Oskari Nikkinen
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Does look suspiciously like an out of scope obstruction like a treeline. Spent a good half an hour scratching my head one night a few years ago wondering why my star shapes had taken a dive off a cliff, and every other sub had extra diffraction spikes with guiding going haywire.

Of course once i actually went and checked the scope it was pointing at a tree. Dont have the subs to show as i scrapped them but did look somewhat similar to yours here.
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deebbecke 0.00
David Ebbecke
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Oskari Nikkinen:
Does look suspiciously like an out of scope obstruction like a treeline. Spent a good half an hour scratching my head one night a few years ago wondering why my star shapes had taken a dive off a cliff, and every other sub had extra diffraction spikes with guiding going haywire.

Of course once i actually went and checked the scope it was pointing at a tree. Dont have the subs to show as i scrapped them but did look somewhat similar to yours here.

Thanks, Oskari!  I didn't get a chance to go back and lookk at the subs as I'd hope to yesterday. I'll let you know what I find.
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