Jump to content

SkySurveyBanner.jpg.21855908fce40597655603b6c9af720d.jpg

Bi-Colour Heart Nebula Mosaic

PhotoGav

By PhotoGav
in Imaging - Deep Sky

Recommended Posts

PhotoGav

PhotoGav

Posted
Posted

IC1805 - The Heart Nebula:

Skywatcher ED80 with reducer

QSI 683-WSG8

Lodestar X2

HEQ5

Ha: Pane 1 = 10 x 1800s, Pane 2 = 8 x 1800s

OIII: Pane 1 = 8 x 1800s, Pane 2 = 9 x 1800s

The different sub numbers were not intentional, simply a result of conditions scuppering collection sessions.

This is a new personal best for integration time, clocking in at a total of 17.5 hours.

post-29321-0-08007900-1414018076_thumb.p

This has been a painful experience. I'm not sure that I am a big fan of the mosaic... It's difficult! I got stuck at 3/4 completion thanks to the weather which left me hanging for about two weeks with one pane of OIII data missing. Finally, despite the wind's best efforts, I managed to collect that final pane last night. I also collected some SII data, which I will eventually put into a hubble pallette version. The original plan was to do a 'natural' looking Ha/OIII version and this is it. I used Noel's actions to make a green channel. There are a couple of patches around the image that probably shouldn't be there, but I'm not certain where they have been introduced during processing!

I look forward to hearing your opinion on this one, good or bad, but hopefully not indifferent!

Surely the weather is set to turn in our favour once the clocks change?!

I then look forward to doing a nice simple single image!!!

Link to comment
Share on other sites
  • Replies 25
  • Created
  • Last Reply
PhotoGav

PhotoGav

Posted
  • Author
Posted

Thank you for your feedback folks.

Regarding the star misalignment... First of all, thank you for highlighting that - it is indeed a problem and hopefully can be solved. I think I know why it is happening, but a solution may be tricky?

I use Nebulosity3 to stack and align subs and also to align the processed Ha and OIII layers. It has worked perfectly, except for the corner areas along the mosaic join... Which are the centre top and bottom. The subs themselves have very slight star elongation in the corners (we'll come back to this problem a bit later) and this seems to be slightly amplified when the subs are stacked, giving more obvious star elongation in the corners of the stacks. So, when I try to align the two mosaic panes by hand in Photoshop, the middle portion of the join is very easy to align, but the top and bottom have obvious star misalignments. My way round that was to locally mask one layer of a misaligned star so that only the other layer's star would show and is nice and round. When it comes to placing the Ha and OIII over each other, the majority of the image is aligned, but those areas where I have masked stars have been masked differently in Ha & OIII, so one star (though round) is not necessarily in the same place on both channels, giving misalignment.

So, how to solve this problem?

Why are the stars slightly elongated in the subs? Is this a limitation of my scope, despite the reducer? The solution would be a perfectly flat field scope, cue Baby Q. Would that really solve the problem though? Is this problem actually down to the spacing between reducer and QSI?

Is the problem in the stacking? Nebulosity seems to be working perfectly though and I have a feeling that the error in the data going in cannot be eliminated by any stacking program.

Perhaps the problem is exacerbated by my poor pane alignment in Photoshop? This is definitely true. I can see two solutions: firstly I can try and mask the same stars in both Ha and OIII - that is potentially an even more painful approach to mosaic building... Have you seen how many stars there are just in those small portions of the image?! The second is to align the panes in a different way, using software rather than my dodgy eyes and hands. The app that comes to mind is Registar - would that make a better job of it? I don't want to buy it to find it doesn't make a difference though and I believe it works on the PC only and my processing is Mac based.

So, your thoughts and solutions on this irritating problem will be much appreciated. Otherwise I will just have to buy that Baby Q and have a large enough field of view to not even have to worry about making mosaics for a while longer!!

Link to comment
Share on other sites
PhotoGav

PhotoGav

Posted
  • Author
Posted

Here's a little update on flat field progress:

post-29321-0-84622900-1414620068_thumb.p

Many thanks for pointing out the star problem as that led me to a fundamental problem in my set up. I had the wrong spacing between reducer and CCD! It now produces a much better flat field (though not perfect...), which has made the mosaic a great deal easier to put together. I have re-captured all the data, though not enough yet...

Please note, this is not a final version of the image, it is a work in progress, really it is just to see if the registration is better.

Link to comment
Share on other sites
PhotoGav

PhotoGav

Posted
  • Author
Posted

Thank you Ruud, Guy & Mark.

Mark, it's mainly down to you for pointing out the dodgy stars in the first place, so a special thank you! It's a shame to lose quite a bit of data, but I feel like I've made a large step forwards as a result, so all is most definitely not lost!

Now all I need is one more night to gather the rest of the Ha data and then process it 'properly'. Though I much prefer this softer version to the first version anyway... Learning all the time!

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.