Red and Green fringing in stars

[thefrogulox (Al)]

Hi all

Another problem for you.

I am doing LRGB imaging with a QHY9 using a Skywatcher Black Diamond 120 ED f/7.5 refractor.

I did my first serious image the other night and captured 100:60:60:60 with Luminance 5 min subs unbinned and RGB 4 min subs binned 2x.

After alignment, stacking and colour combine my stars show red and green fringing. I have attached a zoomed in image of one of the large stars in the image.

I can only gather that the problem is due to one of the following:

(a) filters not being truly parfocal (I have been advised that they are parfocal);

(b) telescope showing colour (I have not seen this in my previous images where I used shorter subs);

(c) internal reflections from stray light; or

(d) focusing not spot on from the get go.

Any suggestions?

[irwjager (Ivo)]

Hi Al,

Any chance you could upload the full image somewhere? It may give use more clues as to what is going on than just a local crop...

Cheers,

[thefrogulox (Al)]

Hi Ivo

I think I figured out the problem (which is too embarrasing to state aloud).

I am going to do some tests shortly (weather permitting) and if I am wrong about the problem, I'll post a full picture.

Thank you for the reply.