I am posting a solution to a problem I was having with my subs, specifically with the UV-IR (L) and the blue filter, in this case the Astrodon E series. I was getting near horizontal lines using the L and B filters, but the G and R filters the subs were always perfect. Then it occurred to me that the L and B filters share the same starting point in the transmission curve, in this case for the Astrodon filters is 380 nm. I wasn't getting good usable data so I bought a new set of Astronomik RGB deep sky and their L3 filter, which start at 420nm. Problem solved! No more unwanted horizontal lines. This was back in early 23, I decided to post this to possibility help someone. Question is, what could be the cause?
Hi Mike, I see what looks like a "repeating" pattern of diagonal bands (not horizontal) in the Blue image, and assume this is what you are referring to. Can you tell me a bit about your setup? eg round 36mm unmounted glass filters, edge blackened What's the scope? 12 inch f/8 ??? Focuser? Rotator? Did you try rotating the filter in its carousel slot to see if the angle of the pattern moves? Did you try rotating the camera in the focuser? Is it in the same orientation in different parts of the sky? Any chance there is an off-axis light source (leak?) It's a bit like some kind of internal reflection, less like an interference pattern.
Hi Colin, Astrodon E series. They come with blackened edges. Yes, my Meade 12" F/8. Moonlight nightcrawler. I didn't try to rotate the filters and I likely had the camera orientated the same. I just found another image of the issue, ngc 2685 using the Lum filter, to me the diagonal lines looks at the same angle, so that should rule out the filters or it's an exceptional coincident. I don't think it's any internal reflection, just prior to this issue I was having very poor subs that I found was due to some light pollution from the neighbor. My setup is at the cottage which is B2-3 zone but some light from the neighbor comes through. I solved this issue with a dew shield and a tarp that I geared up to draw across to block the unwanted light. I included a stacked lum to show what the light pollution was doing, it was awful. So after the light pollution issue was solved then I noticed the other issue with the diagonal lines.
Agreed - they look like they are in the same orientation and place, so I suspect it's polishing marks on the sensor. @Doug can you have a look? Do you have a focal reducer/flatenner in that setup?
Most likely it is etaloning. See https://andor.oxinst.com/learning/view/article/optical-etaloning-in-charge-coupled-devices
