Hi everyone:
I came here because I'm kind of desperate. I've tried to capture the witch head nebula twice this winter (in fact, the only 2 clear nights available). I use a 2600 MM and I was trying to make LRGB. The first night I had an issue with the frames made with the Blue filter (image attached). I didn't do anything and tried to fix it later at home. First I repeated my flats to see if the strange image repeated, but it didn't appear. Then I unmounted the Blue filter, checked that there were no scratches and cleaned it from some dust. . Yesterday I tried again and the problem repeated just the same. I checked Red, Green, Lum and HA images and they were ok. I cleaned it again but with no success.
The filter is a Baader B, 36mm, and it has worked perfectly until now.
I don't know what else can I do. Is it possible that the filter has an "invisible scratch", is it possible that the issue comes from de OAT (WO Z73 reduced) and only happens with blue light?
I only attach the JPG versions of the master B and the B reference.
Thanks in advance.
