Issue with OSC Blue Channel Noise (sometimes) - Forums

Topic starter

Mar 16, 2022 · Edited: Mar 16, 2022

I've been using this telescope, coma corrector, filter and camera for over a year. On two occasions I've ended up with some very strange blue noise in my image.

Here is a single dark corrected and debayered 240sec sub as an example.
https://www.astrobin.com/vqokyo/

Additionally, here is a blink of 80 subs.
https://www.youtube.com/watch?v=3ntoSO11Xcw

Few more notes:
1) This happened to me one other time, but it was a different filter (broadband vs narrowband)
2) Flatts don't seem to have an impact. Flatts do remove the vignette and dust moats, but do nothing for this issue.
3) I gathered data on a second target this night (M78 ) with no issue.
4) This is from PI, but I have checked using Deep Sky Stacker and Siril and they give similar results.

Any thoughts?

Thank you in advance and clear skies!

Nathan

Well Written Helpful Engaging

jewzaam

Mar 16, 2022

I want to say I've seen this when there's a strong source of light causing reflections or leak in the imaging train. I have not seen it specific to a particular channel. Maybe a strong light source nearby with blue or some way that only blue leaks into the imaging train? Just thoughts off the top of my head. Good luck!

Respectful Concise

andrea tasselli

Frequent contributor

Mar 16, 2022

It looks like an issue with the filter, which might happen with steep light cones, with maybe a slight tilt of the filter. The pattern has all the hallmarks of an issue with dichroic filters transmission.

MirachsGhost

Topic starter

Mar 16, 2022

andrea tasselli:
It looks like an issue with the filter, which might happen with steep light cones, with maybe a slight tilt of the filter. The pattern has all the hallmarks of an issue with dichroic filters transmission.

Thank you. The filter drawer I use has a little vertical play. Not a lot, maybe 1mm. What about flex between the coma corrector and the focuser draw tube? Is f/4 fast enough to cause these issues? Sorry for all of the follow ups. I've been fussing with this data since November, and starting to go mad. Just strange that it isn't every image with this setup.

Thank you again.

andrea tasselli

Frequent contributor

Mar 16, 2022 · Edited: Mar 16, 2022

Thank you. The filter drawer I use has a little vertical play. Not a lot, maybe 1mm. What about flex between the coma corrector and the focuser draw tube? Is f/4 fast enough to cause these issues? Sorry for all of the follow ups. I've been fussing with this data since November, and starting to go mad. Just strange that it isn't every image with this setup.

1mm play is plenty to give this sort of issues at f/4, which I reckon is similar to that causing newton's fringes. I don't believe that flexure is a more likely explanation but I can't rule it out as I'm not there. In my imaging trains with similar cameras and filter holders nothing of that sort has ever happened.

daywalker

Mar 17, 2022

process of elimination i guess… remove filter draw if you can mount the filter elsewhere in your image train .

Best wishes 2u.

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