Wizard Nebula with black holes?

[rubecula]

I was inspired to have a go at the Wizard thanks to this wonderful image by MartinB: https://stargazerslounge.com/topic/299571-the-wizard-nebula-ngc-7380-in-bicolour/

My effort is an HOO image made from 15 x 600 sec for both Ha and OIII using an Atik 383L  on an 8" Celestron Edge HD.  I used DSS and then Steve Canestra's method for developing the image in PS.  I've been fiddling with it on and off for days and now think this is the best I can do.  I suppose that getting more data and better focussing might enable me to do better.  I've been struggling with getting good narrowband focusing with a Celestron motor focuser and SGP.  Anyway, here it is:

 

But what's foxed me is the  dark areas around some (but not all) of the brighter stars.  It shows better in this stretched stack of the OIII data:

Any idea what could be causing this?

Thanks

 

Edited January 1, 2020 by rubecula
afterthought

[carastro]

That's come out really well.  No idea about the black areas around the stars though.  ? Dust not calibrated out? 

Carole 

Edited January 1, 2020 by carastro

[CloudMagnet]

Have you used flats? If you have might be worth checking if they are the source of that effect.

If you haven't noticed this before it might not be equipment related, but possibly a side effect of the image processing. It might be worth taking one of the raw images and stretching it to see if you can find any hints there.

[rubecula]

Very perceptive CloudMagnet.  I did use flats, but here is a highly stretched raw sub with nothing else done to it and there's no sign of the dark areas.  So it's a processing artifact.  Now to find out how it got there.

Thanks

[tooth_dr]

38 minutes ago, rubecula said:

Very perceptive CloudMagnet.  I did use flats, but here is a highly stretched raw sub with nothing else done to it and there's no sign of the dark areas.  So it's a processing artifact.  Now to find out how it got there.

Thanks

Robin

A calibrated single sub would be useful.  This would show if the flats are causing it or if it's a stacking issue, or some other issue.  Do you normalise your data or correct light pollution?

[rubecula]

Thanks Adam, I'm not sure what you mean by normalise.  Other than DSS and PS the only other software used on the image was Gradient Exterminator that was run on the stretched images. I'll try calibrating a single sub to see what happens.

I was also going to download a trial copy of APP to see how it compares to DSS/PS.  Is there any particular file structure required for APP?

 

[tooth_dr]

2 minutes ago, rubecula said:

Thanks Adam, I'm not sure what you mean by normalise.  Other than DSS and PS the only other software used on the image was Gradient Exterminator that was run on the stretched images. I'll try calibrating a single sub to see what happens.

I was also going to download a trial copy of APP to see how it compares to DSS/PS.  Is there any particular file structure required for APP?

 

Gradient Xterminator will cause those dark artefacts around the stars.  It thinks it LP and tries to correct it.

[rubecula]

Brilliant, thanks Adam

[carastro]

Quote

Gradient Xterminator will cause those dark artefacts around the stars.  It thinks it LP and tries to correct it.

I knew I had seen that effect before but could not remember where.

Carole 

[tooth_dr]

59 minutes ago, rubecula said:

I was also going to download a trial copy of APP to see how it compares to DSS/PS.  Is there any particular file structure required for APP?

If you get APP up and running, post up any issues you run into.  It uses all the same files as DSS, it just has a different interface.  I still use DSS to do a quick stack on my obsy PC to check progress through the night of my subs, but APP is superior for the main data stacking.