TheGreenDishcloth

@Simon Pepper Thanks Simon, that's an interesting workflow you posted (I sometimes wondered why PixInsight included a noise generator!). I'll give the workflow a shot as soon as I get a moment - I would be great to process this out rather than invest in more kit (although @Louis D's pics provide a strong case for an upgrade 😉 ) The main thing is that I know understand that this is a known issue with cheaper OIII filters - being a newbie, I wasn't sure whether it was either something wrong with my kit or something fundamental I was doing wrong in the processing. Thanks to everyone who replied!

Hmmm, that would be annoying to say the least. I’ve got so much light pollution, the filter is important for most of the targets I’m interested in. The filter does look like the culprit here - I never saw this effect before I started to use it but I also think that I had clean images for a couple of the Cygnus targets before the cold nights in December. Looks like there are a number of things to experiment with. I’ll post an update. Tony

Thanks for the reply! Yes, it’s as close as I can get it. I have the filter in Zwo filter drawer. Any reason it’s so pronounced in the bright stars?

Greetings! This is my first post to the group so please bear with me. I'm new to astrophotography and still getting to grips with many of the practical aspects and I'm hoping someone can help me with this - I've attached a subframe of the Horsehead nebula (300 secs with RedCat 51, ASI 294 MC Pro cooled camera and Optolong L-Extreme filter) - i.e. no processing done on the image. While I've been blown away with the pictures I've been able to get, particularly after recently getting hold of the filter, I've noticed something odd while imaging different targets. I've started to see what appears to be spherical aberration which is really noticeable on some (see "A" and "B" in the photo below) but not all stars (see "C" below) which is kind of odd. The effect on "B" is really noticeable in the processed image (even though I tried to ignore it in the excitement of processing the nebula!). I'm not sure if this is down to the formation of dew or if its something more serious with the scope/filter/optical train. I'm cooling the camera down to -20 to get rid of as much noise as possible but I'm wondering if this is the cause of the problem. As of yet, I've not used dew heaters - would these solve the problem? Any suggestions would be welcome! Thanks in advance Tony