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Been working on this again, still with old data. Loads of gradients that I can't seem to get rid of. I dumped a lot of [NII] subs that had rubbish stars, elongated and trailed.

TS 80mm f/4.4 six-element astrograph, 3nm Astrodons, ASI1600. I think I ran 5 min subs at max DR. Captured in Maxim DL processed in AstroArt5. Sigma Add stack, multiple gradient removals, ans several Histogram Stretch iterations.

Need more data. I have 2 hours of decent HII, but I want to add new [NII] and [OIII].


C&C welcome, and suggestions for further work. The JPEG looks nothing like the FITS I was working on, or how it looks on my monitor from Windows Photo Viewer. Pah!

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Nice detail.... I'm glad to be seeing imaged captured by the ASI1600 since I'm in the market for one.... good work.

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Thanks guys.

Yes, the 3D effect jumped out at me as I was processing the RGB stack.

The original subs have a much wider FoV, unfortunately they are offset at an angle to each other needing a heavy crop. Hopefully the new data I capture (When I can) will be better aligned.

I still need to get rig of some annoying gradients resulting in an uneven background that multiple gradient removal algorithms failed to cure. Cleaner data should help.

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I'd be really interested in seeing the single NB channels side by side..... what does the NII look like compared to Ha and OIII for example?

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Hi Sara

The [NII] is almost as strong as the HII with the [OIII] very weak and noisy by comparison. I'm at work ATM (Naughty!) so I'll see what I can do tonight.

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4 minutes ago, DaveS said:

Hi Sara

The [NII] is almost as strong as the HII with the [OIII] very weak and noisy by comparison. I'm at work ATM (Naughty!) so I'll see what I can do tonight.

Thanks! I'd be interested to see not the different strength in the data, but the actual changes in where the data is.....SII is quite interesting on this one.

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I'll put up the individual stacks, though to get them on here I may have to post JPEGS. I have a Dropbox account (Which I've hardly used) so I'll try to dropbox the original FITS files.

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I'm not worried about the raw data .... Just a quick stretch jpeg to show the difference would be interesting :) 

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OK, for Sara @swag72

Firstly, the HII


Next the [NII]


Lastly the [OIII]


As I intimated, the [OIII] is horribly noisy and all suffer from gradients, the [OIII] worst of all, probably due to imaging in less than brilliant conditions. All are from 5 min subs using the Max DR setting in the ZWO driver.

I will have to recapture good data and dump these dodgy files when I do. I'll probably keep some of the HII data captured most recently.

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Many many thanks for this Dave - Most interesting........ :) 

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Very interesting more data in the N11 image.


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You're both very welcome :wink:.

When I first looked at the [NII] data I thought I'd made a mistake and used the HII filter, they're so similar. I think that similarity is what gives the 3D effect.

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Added more data to the stacks, and dumped some dodgy [OIII] that was very noisy. I also did a lot of pre-processing before stacking. Each set of data was individually stacked and gradient reduced before each group of hydrogen, nitrogen and oxygen data was individually aligned and combined, to give the three components. These were then aligned with each other before each was given a preparatory sequence of histogram stretches. After combining in the NHO palette there was a lot of cropping needed, to get rid of the horribly skewed alignment borders. Another gradient reduction was applied before many small iterations of histogram stretch, with and without curves to give the final result.


Not entirely sure it was worth the effort, as I think my first version was better.

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