Star Halos

[mhamburg]

Forgive me if this has been addressed before. What is the cause and the fix for the small halos around stars (especially around the fainter ones)?
Michael

[admin]

Forgive me if this has been addressed before. What is the cause and the fix for the small halos around stars (especially around the fainter ones)?
Michael

Hi Michael,

Any chance you could post a small (processed) crop of the problem?
Halos are caused by a number of things. If all your optics are perfect (e.g. we can rule out focus and chromatic aberrations), then the usual culprit is atmospheric turbulence (aka seeing), as well as your telescope's diffraction pattern.

[mhamburg]

16X240s@1600iso w/Canon 40D and Orion 80mm ED APO refractor piggybacked on CGEM. Captured w/ BYEOS and guided w/PHD2.

sized_Autosave.jpg (85.15 KiB) Viewed 5042 times

Hi Ivo,
Look especially at the fainter stars. Could this be an artifact from some type of masking during processing that I somehow didn't do correctly?
Michael
ps. When I look at a crop of the star field, now I only see that there is a focus problem. I no longer see the halos!!!

[admin]

Hi Michael,

The stars don't appear offensive to me at all

Could you describe the problem/symptom a bit more and also describe what you would expect to see instead?

Due to your scope's diffraction pattern and (possibly) atmospheric conditions, stars will never appear perfectly pin-point.

StarTools' clipping protection also ensures your stars are never blown out/clipped (sometimes you see these perfect blown out circles in other images from other software). This will indeed preserve (but not create!) halos, but they are real image data (and contain important information about star coloring). This behaviour can be quite important too for retaining detail close to overpowering stars (e.g. Alnitak) or stars shrouded in nebulosity (ex. Iris nebula).

However, if the halos bother you, try the Magic module's "Tighten" algorithm on the offending stars (and their halos) in a star mask. this algorithm was specifically designed to 'Tighten' the halos around the stars towards their core.

[mhamburg]

Thanks for the reply, Ivo. The halos seemed to have disappeared when I saved the original .tif to a .jpg format. (Or maybe I have been looking at these images for too long? )