NGC 7023 Iris nebula revisited

[EyeGuy]

So after Carole helped me to realise that I was taking my flats wrong, I've reprocessed this image and finally the funny rings have vanished.

Original thread

TL;DR - I was underexposing my flats, which resulted in failure of calibration to remove vignetting, as well as it introducing weird red concentric oval rings.

Last night was supposed to be clear, so I set up in the garden. Cue the Irish weather. I only managed to get PA and focus (you know, the most fun bits) and then the clouds rolled in.

Anyway, so instead of imaging, I took a bunch of calibration frames. The setup was slightly different to the lights -

1) temp 4 C instead of -1.5 C (no big deal)

2) camera at different angle to telescope (can't correct dust motes)

3) new camera angle adjuster in path (different vignetting and internal reflections)

so I didn't hold out much hope that it would correct the problem. But it did! I used the new bias and darks to correct the new flats, and then the old bias and old darks and new flats to correct the lights. I'm so pleased I've finally figured out what was going on as it's ruined many images for me over the past year+.

Thanks again Carole,

Barry

 

[tooth_dr]

Wow Barry. They dust just seems to really be hanging in the vacuum of space. Stunning!!

You have a reasonably dark site?

[EyeGuy]

2 minutes ago, tooth_dr said:

Wow Barry. They dust just seems to really be hanging in the vacuum of space. Stunning!!

You have a reasonably dark site?

Thanks!

Sadly not that dark - I live in Derry, but this was from the Ballycroy International dark sky site, which is down in Mayo. That's actually the main reason I wanted to resurrect the image - I was only there 1 night with clear skies and a new moon.

Barry

[tooth_dr]

34 minutes ago, EyeGuy said:

Thanks!

Sadly not that dark - I live in Derry, but this was from the Ballycroy International dark sky site, which is down in Mayo. That's actually the main reason I wanted to resurrect the image - I was only there 1 night with clear skies and a new moon.

Barry

I can understand why you would want to make the most of the data!  It's a stunning image, you've really go it sussed, and taking calibration data weeks after the lights!

I too popped out last night, and as you say it just wasnt playing ball.  At least you got the fun stuff done.

[EyeGuy]

3 minutes ago, tooth_dr said:

I can understand why you would want to make the most of the data!  It's a stunning image, you've really go it sussed, and taking calibration data weeks after the lights!

I too popped out last night, and as you say it just wasnt playing ball.  At least you got the fun stuff done.

It was surprisingly straight forward to do actually - I'm really no guru with PI. It was just a matter of making a new master flat and hoping for the best. I can hardly believe it worked after 3 weeks. I had to crop a fair bit out at the edges as the correction only worked well in the centre, but the best bits were decently corrected. Thanks again,

Barry

[Jkulin]

Hi Barry,

I know I am old and decrepit, but I put your old and new images in the same frame and I still can't see a difference between the two: -

 

The top image is the original and the bottom is the revised.

[EyeGuy]

27 minutes ago, Jkulin said:

Hi Barry,

I know I am old and decrepit, but I put your old and new images in the same frame and I still can't see a difference between the two: -

The top image is the original and the bottom is the revised.

I don't think the bottom one is the new one. I think it's just a copy of the top one. The framing is slightly different in each shot as it was completely reworked. Those 2 have identical framing.

You had me doubting myself there!

Barry

[Jkulin]

Nah Barry I copied them separately, I've redone it and cropped to make them a similar size and this was the link to the files: -

 

I wonder if the cache isn't refreshing, but it shoudl do as the files are different names.

I'm just hoping it isn't my eyes going bad in my old age!

[EyeGuy]

44 minutes ago, Jkulin said:

Nah Barry I copied them separately, I've redone it and cropped to make them a similar size and this was the link to the files: -

 

I wonder if the cache isn't refreshing, but it shoudl do as the files are different names.

I'm just hoping it isn't my eyes going bad in my old age!

 

Hi John, now I can see a difference!

But don't worry, you're definitely not the first one that couldn't see it.

If you go to the original thread and scroll down a bit you'll see that some forum members have kindly posted annotated stretches of the image to demonstrate the effect. It's subtle for sure but it's one of those things that once you see it, you can't see anything else but it! It was driving me absolutely nuts!

Barry

[Jkulin]

No Probs Barry, apologies for being a pain, I just couldn't see it and am normally super critical of my own stuff, that why I rarely publish my own.

Glad you have sorted your apparent problem....lol

[Allinthehead]

That's a very nice improvement Barry. Nice to see the issue resolved.

[EyeGuy]

51 minutes ago, Jkulin said:

No Probs Barry, apologies for being a pain, I just couldn't see it and am normally super critical of my own stuff, that why I rarely publish my own.

Glad you have sorted your apparent problem....lol

Not at all! Thank you for looking at them. You really weren't the only one who couldn't see the problem initially!

Barry

[EyeGuy]

54 minutes ago, Allinthehead said:

That's a very nice improvement Barry. Nice to see the issue resolved.

Thanks. I'm so pleased to have fixed it. I now find myself unable to wait for the next clear night!