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M27 Two Ways


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This wasn't an intended target of mine this year, but after realising just how bright it was following a single 2minute test sub and being directly overhead, I decided to pile on the hours and go for the fainter shells on this one. Starting with clear skies in the last waning Moon phase, a run of 4 clear nights in a row (28th - 31st July) followed by two more (3rd and 4th August) I collected 17 hours of RGB data over 6 nights using my 585mc during both Nautical and Astro Dark as it returned.

After 17 hours, I was hopeful of those fainter details. But, somewhat disappointingly, the outer shells remained elusive; they are there in the data, but are still very faint. And masked partially by the colourful starfield in the final process.

M27_RGB.thumb.jpg.250f1b59fd289d6b7c7aa796b425aa35.jpg

With more clear skies predicted, I decided to give up on RGB and swapped over to a dualband filter, and collected a further 10 hours of data over 4 nights (6th, 11th, 12th and 13th August) - 3 more in succession! And who says the summer months are bad for imaging !!!

Next task was how to combine the RGB with the Ha/OIII data that I had collected. After some trial and error using PI's NBRGB combination script, I finally managed a HOORGB rendition:

M27_HOORGB_Combination.thumb.jpg.bb31b5795df1f67ffa179babf1e8e58e.jpg

REVISION A POSTED FURTHER ON DOWN

Z_NBRGBCombination_STR14.thumb.jpg.667bc45ee4dfdff9880910e04c7ec508.jpg

There are those outer shells! Combined with RGB stars.

I don't recall processing a HOORGB image previously, but I do find the colour change rather interesting. Whether this is me making a mistake during processing I am not sure. Both images were treated to a run of SPCC, and in the case of the dualband, this was prior to removing the stars and splitting the channels.

With hindsight, I probably should have opted for the dualband filter from the outset, after all, 10 hours of HOO showing those shells, I can only imagine what 27 hours would have brought me. I might still add to it since I can see fainter details teasing me to try and capture them, but at the same time I feel like I want to move on now to something else.

Equipment: ZWO ASI 585mc + Starfield 102ED + 0.8 Reducer on HEQ5
Filters: Astronomik L2 UV/IR Filter & Askar D2 Ha/OIII
Gain - 252
Frames - 343 x 180s (RGB) + 100 x 360s (NB)
Calibrations - 25 darkflats, 20 flats per session.
TOTAL TIME: 27:09:00
Stacks in SIRIL
Edited in Pixinsight, XT Suite, Starnet2, GraXpert and GIMP

Comments welcome as always :) 

Edited by WolfieGlos
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I would try an ImageIntegration to 'combine' them. You should save the files first and use two instances of each as the ImageIntegration requires at least three files. This process increases a final SNR. 

 

Edited by Vroobel
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1 hour ago, Vroobel said:

I would try an ImageIntegration to 'combine' them. You should save the files first and use two instances of each as the ImageIntegration requires at least three files. This process increases a final SNR. 

 

Thanks Vroobel, I’ll have a look for that. I assume this would be done during the linear stage? 

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32 minutes ago, WolfieGlos said:

Thanks Vroobel, I’ll have a look for that. I assume this would be done during the linear stage? 

Yes, but you loose nothing if try both ways, your images are already processed after all. 🙂

 

Edited by Vroobel
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Nice job Chris!  Both really good images.

How did the dual band filter image itself look Vs the combined as far as shells and detail? 

13 hours ago, WolfieGlos said:

TOTAL TIME: 27:09:00

Serious time spent too, very impressive!  

13 hours ago, WolfieGlos said:

With hindsight, I probably should have opted for the dualband filter from the outset

Hindsight is great :D It's always worth experimenting and the resulting RGB image is still very nice, with the faint shells still just coming through nicely out the background.

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7 hours ago, Vroobel said:

Yes, but you loose nothing if try both ways, your images are already processed after all. 🙂

 

Will give it a go when I next get a chance, thanks 🙂

5 hours ago, simmo39 said:

Like that a lot, I must try the HOORGB combo myself.

Thanks simmo! Yeah, give it a go, look forward to seeing what you produce 👍

4 hours ago, geeklee said:

Nice job Chris!  Both really good images.

How did the dual band filter image itself look Vs the combined as far as shells and detail? 

Serious time spent too, very impressive!  

Hindsight is great :D It's always worth experimenting and the resulting RGB image is still very nice, with the faint shells still just coming through nicely out the background.

Thanks Lee!

The dualband filter looked largely the same to be fair, only without the RGB stars. The 17 hours of RGB added very little to it, which makes me think perhaps the method Vroobel has described would have worked better.

Yeah, that amount of time across several nights running was doable thanks to my wife looking after the baby! And a completely clear night every time.

The RGB image showed the outer shells after only 4 or 5 hours if I recall, I just continued to pursue it but the gains were only very slight each additional night. I can’t help but wonder if the Nautical Darkness has played a role in it here?

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30 minutes ago, TiffsAndAstro said:

I got my own M27 up to 6.5 hours broadband, but I'm struggling to process it.

Hopefully can do some NB on it soon use the broadband as stars 

Share the stacked, unprocessed image, and I’m sure people will give it a go and provide pointers. We’ve all done it 🙂

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19 minutes ago, WolfieGlos said:

Share the stacked, unprocessed image, and I’m sure people will give it a go and provide pointers. We’ve all done it 🙂

Will do. Don't want people to process it for me, but would love some insights.

Main one likely to be I need to use a mask for the outer stuff. Inner stuff I dunno.

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1 hour ago, WolfieGlos said:

I can’t help but wonder if the Nautical Darkness has played a role in it here?

Agreed, it will have had an impact in RGB, and to a lesser extent in narrowband.

Looking at the tidy, low noise background, there's probably a touch more to stretch in those faint shells - tricky against the bright core though.

1 hour ago, WolfieGlos said:

thanks to my wife looking after the baby! And a completely clear night every time.

Great stuff :) :)  mine is also very accommodating with "family and life stuff" when rare clear skies arrive, I'm always extremely grateful.  I don't think I've ever seen as many clear nights as that in a row though 🤣

Edited by geeklee
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25 minutes ago, TiffsAndAstro said:

Will do. Don't want people to process it for me, but would love some insights.

Main one likely to be I need to use a mask for the outer stuff. Inner stuff I dunno.

Inner is easy and can be achieved with a few curve stretches. But for the outer, yes, masks will be needed unless you want a blown out core. Can be done in GIMP, I did mine in PI.

14 minutes ago, geeklee said:

Agreed, it will have had an impact in RGB, and to a lesser extent in narrowband.

Looking at the tidy, low noise background, there's probably a touch more to stretch in those faint shells - tricky against the bright core though.

Great stuff :) :)  mine is also very accommodating with "family and life stuff" when rare clear skies arrive, I'm always extremely grateful.  I don't think I've ever seen as many clear nights as that in a row though 🤣

When I started, we had an hour of astrodark so I wasn’t concerned about nautical darkness. I’d estimate that for the BB and NB that 75% of the total time is nautical darkness, like I did over the summer months. Maybe I’ll see if I can isolate those subs and see what a stack looks like.

Ill try another stretch , see what I get 👍

Glad to hear Lee, same for me being grateful. Mine is very supportive too but even on that run it became a bit of a stretch for her lol. Luckily working at home 4 days a week helps. I think I had 3 in 5 days last year, but yeah, this was a very good run and too good to miss out on.

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Posted (edited)

Take #2 on the HOORGB version.

I've taken a step back and realised that for the HOORGB image posted in the OP, that I had used the non-linear RGB file and then added linear Ha and OIII to the image.

This time, I've processed both versions from scratch in linear, removed the stars and then combined with the NBRGB script and processed from there. I've also used curves and layer masks in GIMP instead of range masks in PI, and this time around the Ha is a lot more striking.

@Vroobel I tried the Image Combination, but it wouldn't give a satisfactory result, so I went back to the script.

Comments welcome as always :) 

Z_NBRGBCombination_STR14.thumb.jpg.667bc45ee4dfdff9880910e04c7ec508.jpg

 

Edited by WolfieGlos
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I meant ImageIntegration (process), not CombineImages (script) if you used it. 🙂 BTW, I wasn't precise enough. I assume you operate on two files with the same geometry that means they were stacked in the same WBPP run and automatically cropped or one image is registered according to the second one. Moreover, I think you should select Maximum here:

Screenshot_20240821-042601__01.jpg.6e7902acf11fafe1473b15bb592c6d93.jpg

and 'No rejection' here: 

Screenshot_20240821-042601__03.jpg.a1ad8189373dfe1dbb8563c2073b00ae.jpg

Also, I think 'SNR' should be selected here:

Screenshot_20240821-042601__02.jpg.586635aec90dd00ce6c32e5cb677a224.jpg

Use a global execution (blue filled circle) as last:

Screenshot_20240821-043156.jpg.e95a50f593ed9f2eff2e6b11fac4564e.jpg

Could you share the masterLight files, please? I'd like to check whether my suggestion makes sense... 😁😉

*

Screenshot_20240821-042601.thumb.jpg.c0700a0b2cc4f7f445b34f9007aeed05.jpg

https://pixinsight.com/doc/tools/ImageIntegration/ImageIntegration.html#description_001

 

Edited by Vroobel
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Great M27, the overall structure and faint features are akin to AN's Picture of the Month, and that's a NB/RGB composite of 32 hrs with a Planewave CDK 17 from the Sierra Remote Observatory...👍

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6 hours ago, tomato said:

Great M27, the overall structure and faint features are akin to AN's Picture of the Month, and that's a NB/RGB composite of 32 hrs with a Planewave CDK 17 from the Sierra Remote Observatory...👍

Thank you Steve 👍 Do you have a link to that Planewave image, I can't find it for some reason?

I'm sure I can see some faint Ha on the edges of the upper right corner, so I'm tempted to pump in some more hours and see if it's there. If the CDK image doesn't show it....I won't bother :D 

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Wow, that's really impressive! Thanks for linking it @tomato.

Looks like I'm right about the Ha to the edges although I suspected it went out further still. They've got some lovely detail in the Ha streaking outwards from the core.

Possibly a bit too saturated for my liking, and I know colour is somewhat subjective, but it's interesting that they have blue as did @ONIKKINEN in his recent M27 (which is also superb). Can't help but wonder why mine came out green, which is very similar in shade to what Siril has for the OIII bandwidth, so I presumed it was "correct".

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@WolfieGlos I think there are almost as many different variations in colour palette as there are images of this target out there just because a tiny adjustment will have a huge effect on the end result and we all have different tastes. As for my own image i just reduced the green a bit in Photoshop, but left some in for a slight teal look to the OIII nebulosity. No real science behind that decision, just think too much green looks strange in astrophotos probably because it is not that common in most targets, just a matter of taste. Im not sure there is a clearly right or wrong palette, but if i had to say there is i think the green is more real than not having it.

I think many use SCNR green in Pixinsight, which does the same thing as fiddling with the balance manually in Photoshop, but i like leaving this final tune in towards the end of the process so dont usually do it in PI. The full blast 1.0 strength SCNR green results in a blue-red image, something between 0-1 results in a more teal image without the strong green hue.

Edited by ONIKKINEN
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15 hours ago, ONIKKINEN said:

@WolfieGlos I think there are almost as many different variations in colour palette as there are images of this target out there just because a tiny adjustment will have a huge effect on the end result and we all have different tastes. As for my own image i just reduced the green a bit in Photoshop, but left some in for a slight teal look to the OIII nebulosity. No real science behind that decision, just think too much green looks strange in astrophotos probably because it is not that common in most targets, just a matter of taste. Im not sure there is a clearly right or wrong palette, but if i had to say there is i think the green is more real than not having it.

I think many use SCNR green in Pixinsight, which does the same thing as fiddling with the balance manually in Photoshop, but i like leaving this final tune in towards the end of the process so dont usually do it in PI. The full blast 1.0 strength SCNR green results in a blue-red image, something between 0-1 results in a more teal image without the strong green hue.

I did research the colour on Google (which mostly turned up CN, SGL and Astrobin), and it seems to vary quite a lot between blues and greens and I agree, the green does look odd. There doesn't seem to be a general consensus either from what I can find.

I did try a process to turn it blue (with yours as a reference actually), but yeah, it just didn't look right on my image - that's probably more from my lack of ability than anything else. But on yours, it looks superb.

On my broadband only image, SPCC turned it blue as seen in the original post. I'm not going to get too hung up on it, it's only that I struggle with colour balance at times so I do question myself a lot - more so here than any other target I've imaged so far.

I usually run SCNR on about 0.5 for most of my images, I did it for the stars on this one, but the background didn't need it after Graxpert effectively did it for me.

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13 hours ago, ollypenrice said:

This is a very good M27.  I think the star colour is best in the last one.

Olly

Thanks Olly, appreciate the kind words. I used SCNR on the stars in the revised HOORGB image, which I forgot to do first time around, so I am glad that it’s made a visible difference 👍

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