Hi Steve, Phil and Peter
Really enjoying my time on Pier 5 - and thanks for all the wonderful service to date.
I am still having a problem with star halos, which appear on pretty much all images. I attach an image of the Helping Hand nebula, after almost 300 x 180sec subs. The halo around the stars are clearly visible, and this picture can be compared to the Astrobin image
https://www.astrobin.com/bsyt9q/ which is a 25hr exposure with a Tak FSQ106. It goes much deeper and has no halos.
I have tried to restrict the data set to see if the problem is due to high cloud - but a subset of the "best" (in terms of star counts/noise ratio and visual inspection) still has the identical level of halos.
Funnily enough, on my home 'scope (GSO RC8) I had the same problem, and I originally put it down to high cloud/haze. But it didn't go away and I resorted to asking my friends on Astrobin (I was quite a likely thread a week or so ago). The issue was correctly diagnosed - and quickly fixed - to a dewed up secondary. The problem was barely visible to the naked eye, but, boy, did it make an immediate difference when I cleaned it. Indeed, my subsequent image of NGC1097 immediately gathered a top pick nomination - probably more of of pity than anything else. I have also cleaned my primary since and hope for further improvement.
There is also a "gut" feel that the system is not going as fast or as deep as I expected it would. This would also be consistent with dew/dirt. To some extent this is confirmed by requests for fellow subscribers for more data - even in fields without bright star halos. I have also processed the most recent data on the Perseus cloud mosaic. The mosaic is shaping up well, but the noise is much higher than I would expect for 5hours at f2.8. I am having to using a much higher level of noise reduction than I would normally use.
Again this is similar to my experience with a dewed RC8, but of course, I don't know your system like you do.
Grateful for your thoughts on this matter.
1) Could it be due to a dewed/dirty secondary (or primary for that matter)?
2) Is this a feature of the Tak180ED 'scope? I know some widefield scope e.g. RH Veloce has large halos due to size of 2ary obstruction), but I haven't heard of this being an issue with the Tak. If so, perhaps I am simply better off avoiding bright stars.
3) Have we had a particularly bad month with omnipresent high cloud?
Best regards
Brian