"Halos" on stars

[Zakalwe]

Attached is a crop of some M101 data that I took last night. it is a stack of 16 x 200 sec, 10 x 150 secs lights and 11 x 200 sec darks. They have been stacked in DSS. Focus was achieved with a Bahtinov mask. All taken on an unmodified canon 50D, SW Equinox 80mm Pro, SW field flattener and SW LP filter.

When you zoom in, some of the stars appear to have dark centre with a halo around them. Some have a bright centre and a concentric dark and light band....they almost look like Airy discs.

What is doing this? Is it normal? bad focusing? Bad tracking being averaged over the stack?

[Psychobilly]

Has the image been cropped as well as resized... ?

If its been cropped any chance of posting the full frame but reduced in size and some larger cops of the problem stars and where they have come from in the image.

Billy...

[Zakalwe]

Thanks for the reply Billy.

Not, it is not cropped, but it was stacked using the Region of Interest in DSS, to cut down on the stacking time.

Would a full frame sub help? Or should I restack using the full frame?

[Psychobilly]

A full frame sub will be enough as long as you can see the "effect"...

[Zakalwe]

A full frame sub will be enough as long as you can see the "effect"...

Ahhh...now that's interesting. I have looked at a couple of the RAW files. No sign of the effect, though one or two subs have a wee bit of trailing when viewed at 100%. I guess that a couple of those would mean that DSS is averaging out the trails. crating a "halo"?

I think that I will go through the stack again with a more critical eye and delete anything that has any trailing?

[Psychobilly]

Definitely worth doing that first and see what happens... Going to be out for a few hours will catch up later...

Billy...

[Zakalwe]

Thanks fella...I appreciate you taking the time.

[SteveL]

Isnt this DSS and the fix cosmetics options? Clean hot pixels/clod pixels?) Have seen this asked before with dark centres on stars, and turning off the costmetic options fixed it first time.

[Zakalwe]

Isnt this DSS and the fix cosmetics options? Clean hot pixels/clod pixels?) Have seen this asked before with dark centres on stars, and turning off the costmetic options fixed it first time.

Hmmm...I have re-stacked them, and chucked out any less than perfect subs. Still got the dark stars, so will try unchecking the cosmetic tickbox.

[Zakalwe]

Isnt this DSS and the fix cosmetics options? Clean hot pixels/clod pixels?) Have seen this asked before with dark centres on stars, and turning off the costmetic options fixed it first time.

You, Sir, are a genius. Please send me your fax number so I can fax a £50 note to you by way of thanks:D

Deselecting the Cosmetic "Detect and Clean Hot Pixels" has returned my star cores to me.

Thanks very much:icon_salut:

[SteveL]

I just remember seeing this problem and fix a few times in various places, so it was worth mentioning it here to save your sanity

[Psychobilly]

Cheers Steve one to watch for

Billy...