Help with diffraction-like spikes - blue channel only

William Optics Redcat 51 ZWO ASI2600MM Pro Processing Deep Sky Artifacts
7 replies•217 views
David Ebbecke avatar
David Ebbecke avatar
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 

Well Written Respectful
Chris White- Overcast Observatory avatar
Chris White- Overcast Observatory avatar
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…
Oscar H. avatar
Oscar H. avatar
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.
David Ebbecke avatar
David Ebbecke avatar
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.
Well Written Respectful
David Ebbecke avatar
David Ebbecke avatar
Oscar H.:
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.
Well Written
Oskari Nikkinen avatar
Oskari Nikkinen avatar
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.
Helpful Concise Engaging Supportive
David Ebbecke avatar
David Ebbecke avatar
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.
Related discussions
Blue "stars" in image of NGC 55
I've been working on an image of NGC55 from The Astro Imaging Channel (YouTube) 2023 Workshop. It includes LRGB and Ha from Terry Robison. The attached image is an LRGB… I have not added the Ha. At first, I thought the blue specks were star...
Blue channel anomalies in stacked images; similar processing artifact investigation.
Jul 2, 2023
Reduced CA without AI
I tried an old (as I’ve now learned) method, fueled by frustration, to reduce chromatic aberration in my images. I’m shooting with a Explore Scientific ES-ED102, a ZWO ASI 2600MC PRO, and an Optolong L-Para. The Method: After loading the final stacke...
Addresses chromatic aberration reduction, relevant to purple spike artifacts.
Feb 7, 2026