Can someone advise me please?

Hi Folks,

I wonder could one of you imaging gurus advise me on an image of M81 in the link attached please?

M81 10th Feb 2 hrs Exposure

There are colour patches at the periphery of the image which I can't explain. I took another photo of M81 a few weeks previously which had no such issues, see this link

M81 1st Feb 1hr Exposure

The only major difference between these two images (apart from exposure time), is that I used AUTODARK on the 1st Feb image. I am wondering if the colour fringing on the 10th of Feb image is due to insufficient dark frames? Or is there something else I'm not thinking of?


Many thanks and clear skies!


Dave

Hi Dave, it looks strange alright, the 10 feb image artefacts look broadly rectangular to me, this may be a result of post processing?

I know in photoshop thd colour balanced of am image is dictated somewhere between green and magenta, though I really can't explain it here

Hi Dave, it looks strange alright, the 10 feb image artefacts look broadly rectangular to me, this may be a result of post processing?

I know in photoshop thd colour balanced of am image is dictated somewhere between green and magenta, though I really can't explain it here

Did you use 'binning' whereby pixels are combined together on the basis of associated colour?

Keith..

Hi Keith,

Many thanks for your reply. I had thought of something like that and went back to the original images. They are present in the raw data, so I had ruled out a processing artefact. These artefacts also have RGB data associated with them, so it is broadband light coming from somewhere. I reviewed all the books I have on it (including Wodaski), I see nothing explaining this. I should add, that I don't have a light pollution filter (need to wait for Santa on that one...or the lottery).

So I had thought it was sky glow, light pollution or the fact I didn't have enough darks. I am west of the city and was imaging high over the city, so to me light pollution is a contender, but it does not fit with what I see in the books. I can probably eliminate the darks myself by reshooting the image with AUTODARK switched on. I'm just reluctant to use up a precious nights imaging when I could ask a question first!

Clear skies


Dave

Any possibility that it is pixel reflections of off CCD window?
Try a high quality flat (take many and average them).

Mark C

Hi Mark,

Thanks for your inputs. I did take 12 flats and average them together to create a master flat. I wonder if perhaps somewhere along the way I made a mistake? I might go all the way back to the raw data and reprocess the whole lot from scratch.


Thanks for the idea


Dave