Can anyone explain this optical effect?

[Euan]

There's an effect I've noticed quite a lot in really good images and I can't quite see how it's achieved

It's in a lot of Rogelio Bernal Andreo's images, and I've just noticed it in this one from Harel: http://stargazerslounge.com/imaging-deep-sky/117024-ic-59-sh2-185-ic-63-a.html

There is quite a bit of glow around bright stars, and it really shows off the star colour well, what causes this? I really like it, I think it adds a lot to the final image, especially when you have different star colours

With credit to RBA and apologies for the plagiarism, here is a snippet of what I mean (this one is Betelgeuse):

[brianb]

(1) Thin high cloud

(2) Dirt on the lens!

(3) Halo added by software in post processing

(4) Some combination of the above.

[RBA]

(1) Thin high cloud

Doubtful.

(2) Dirt on the lens!

Hey! Umm... Well, the lens of my FSQ isn't what you'd call CLEAN at this moment but...

(3) Halo added by software in post processing

No way

(4) Some combination of the above.

Actually, it pretty much "just happens" on really bright and colorful stars, such as this one or for example, Aldebaran (mag 0.87) in my Hyades shot. It's especially noticeable on red giants, but it too happens on bright blue stars as well.

Anyway, glad to be here! Like I told Harry, I may not be a regular all the time, not because I don't like being accessible but because I feel I'm already in more astro-related forums, groups, etc than I can handle (I'm sure you all know the feeling) and I'm known for having failed before at other forums, but I'll do my best to stop by often.

[Euan]

You can't beat straight from the horses mouth

Welcome to SGL!

[angusb1]

You can't beat straight from the horses mouth

Welcome to SGL!

Welcome to the forum Rogelio.

[harry page]

Hi

Welcome the masterful mr RBA

We would welcome any words of wisdom you have , even if its only now and again

Harry