Helix HOO - NII data

[Slawomir]

Hi all,

Sharing my first attempt at combining Ha and OIII data for the Helix. I am hoping to also add NII data in the coming weeks to put together a tri-colour image.

Acquisition details:

CFF 105mm at f/4.5 (with Riccardi reducer)
30 hours of OIII
38.5 hours of Ha

A link to Astrobin: https://www.astrobin.com/full/362928/0/?nc=user

Version with a touch of noise reduction: https://www.astrobin.com/full/362928/B/


Third version with a more aggressive histogram stretch: https://www.astrobin.com/full/362928/D/?nc=user


This is my first planetary nebula, so colours and processing certainly need refinement.

Thank you for looking
Suavi

[miki63au]

:eyepop: Amazing ... very sharp



Mick

[strongmanmike]

Excellent Smithers...exccellleeent :evil2:

[RickS]

A great start, Suavi!

[cometcatcher]

Looks great Suavi! How did you get neutral colour stars in a bi-colour image?

[vlazg]

Fantastic Helix Suavi, looking forward to the NII

[Peter Ward]

Things I'd fix...

Colours are too pastel.
Stars show no colour variation...RGB field stars would be cool.
A deep luminance channel may well reveal the many faint fuzzies also present but not seen here so far...it's tough with 105mm of aperture.

That said...

Gee, the data is so tight....a few tweaks and dare I say... you'll
have an award winning result.

This is really great stuff. :thumbsup::thumbsup:

[Placidus]

Excellent acquisition and processing, and with 4% of the photon flux we threw at it. Brilliant.

[troypiggo]

Rounds and tight stars across the field - always the foundation for an awesome image. Well done. :)

[Ryderscope]

The deep detail of the nebula has come through well Suavi.

[gregbradley]

Lovely colours and tight details. A high class Helix.

Greg.

[Slawomir]

Thank you all for such kind feedback.

It has been my longest exposure by miles and I enjoyed slowly adding data from night after night. ICX in QSI body is very clean - having signal only 1 ADU above the floor (about 0.25e) and there is absolutely no sign of any glow or fixed pattern even with an extreme histogram stretch. I did not use darks and did not apply noise reduction nor decon.

The thin long bow/shockwave at the 'top' of the Helix gets only one photon per pixel per hour of exposure with my set up - I personally think it's remarkable that an average amateur has access to technology allowing to capture such faint signal.

Kevin - Creating starless master HA and OIII and combining those for RGB allows for neutral star colours in narrowband images.

RGB stars are certainly on the cards, thank you for the advice Peter. Let's hope weather will be good later next week after the Moon will start moving away from the Helix.

Who knows, maybe I will be lucky to reach a century with the total exposure for this image :)

[graham.hobart]

EEK! A giant effort mate and one smooth lookin eyeball. lovely!:eyepop::thumbsup:

[Geoff45]

Great stuff Suavi, although I would agree with Peter that the colours are too pastel.
Geoff

[Camelopardalis]

Beautiful image Suavi :thumbsup: way deeper than we can catch here in Brisvegas...

[Paul Haese]

Nice detail Suavi. I also don't mind the colour, maybe a bit pink but I think it is ok. I like the outer chevron detailing, it only comes with integration. At full resolution it is an interesting image to cruise around.

[Slawomir]

Thank you all again for encouragement and feedback.

I find it a bit tricky to balance colours with bi-colour data, so I will leave it as is and play with colours again, once I finish collecting NII, and hopefully will then add RGB stars as well.

Applied a touch of noise reduction and tried to bring out the outer details within reason: https://www.astrobin.com/full/362928/B/

Thank you for looking
Suavi

[Atmos]

It's more of a pink than a red that you find in many of the HOO images of Helix but I quite like it.
Very nice and VERY smooth :) :thumbsup:

[Slawomir]

Thanks Colin. It might have been my mood on that day subconsciously directing my processing towards pinkish colours :lol:

Anyway, I was just having a go at processing the data since there is one more channel yet to be added at some point to the image, and also RGB stars as well.

[Slawomir]

Hi all,

I tried to squeeze a bit more out of the data I have: https://www.astrobin.com/full/362928/D/?nc=user

Focus was on showing the outer bits - colours will be adjusted once I complete collecting NII data.

Thank you for looking
Suavi

[Ryderscope]

It will be interesting to see where the NII takes this Suavi. I’ve wondered how much data there is to be had from NII for these objects.

[gregbradley]

I like the extra details you brought out but it seems to have lost colour saturation in the process.

Greg.

[Atmos]

Those fainter areas are showing up really well Suavi :)

[Retrograde]

Great result Suavi. Love seeing those faint outer shock-fronts.

[Placidus]

The new stretch is simply stunning.

:eyepop:


A magnificent result.

[Slawomir]

Signal in NII is quite strong for the Helix, that's probably why people get good SNR more quickly with 5nm Ha for this target.

I will post NII master after I collect the data.




Thank you Greg for your feedback. I am still not quite happy with the colours but hopefully the final tri-colour image will be more satisfying.



Thank you Colin. I have never before pushed my data this much, so all of that is a new territory and experimenting has been quite enlightening :-)



Thank you Pete. This project was intended to be a quick one (10 hours per channel), but somehow I kept adding more and more integration to see how much can my small refractor reveal.



Thank you Mike and Trish.

I have not been using darks for calibration in my images, but in the coming days I will collect some darks and see if that helps in rescuing a few more photons from the camera-induced signal.

[willik]

I like it a lot
Martin

[Slawomir]

Glad you like it Martin.

Feedback from fellow astronauts made me thinking about trying to squeeze a bit more out of the data I have already, and I also got an advice to use darks in calibrating data as I have not been using darks at all.

So I completely recalibrated Ha data with fresh bias and dark frames and tried fine-tuning pixel rejection settings and carefully picked a reference frame and....happy days - SNR for the Ha master improved by nearly 2% and st.dev for background (background noise) has decreased from 1.25 ADU to 0.92 ADU. That's about 0.24e for my camera for Ha master made from 15-minute subs.

Later I will recalibrate OIII data in an attempt to rescue a few more photons.

Also NII data collection has been scheduled to resume tonight.

[Slawomir]

Update 30/08/2018

Hi all,

I braved the Full Moon and acquired about 20 hours of NII data of the Helix when it was positioned on the sky quite close to the moon. I will need to carefully calibrate with flats and remove gradient from the Moon glow, and the data is not as clean as Ha or OIII that were captured during darker nights, but nonetheless NII seems to be a bit different from Ha and I look forward to combining all three channels into one image of the Helix.

Attached are histogram stretches of NII (left) and Ha (right).

Thank you for following my progress with this project.

Suavi

EDIT: I am wondering whether similarities between the Ha and NII is due Ha signal leaking into NII and NII into Ha even with 3nm filters...

[Ryderscope]

Interesting to see where this is going. I don't see a lot of additional information in the NII but processing further might bring this out. I see that the 3nm Ha and NII fitlers do overlap quite a bit so some duplication would be evident.

[Slawomir]

Thank you Rodney for the graph - yes, there is some overlap plus not sure whether wavelength shift at f/4.5 would cause even stronger mixing of Ha and NII.

The most noticeable difference is that NII has the weakest signal out of the three filters near the central's star remnant, with OIII being the strongest, perhaps also outer bows and shockwaves are less evident with NII as opposed to Ha.

Also, NII seems to have more strongly defined structures in the nebulosity surrounding the central star.

[Andy01]

Following with interest Suavi.
As you know I too have a 3nm Astrodon NII filter and I am co-incidentally gathering data on this very same object.
From past experience, mapping Ha/N2/S2 is rewarding but challenging- but it can be done with pleasing results. Ha/N2/O3 is going to be interesting!

http://www.parkes.atnf.csiro.au/news_events/astrofest/awards/2018images/HM_Deep_Andrew_Campbell.jpg

I look forward with great enthusiasm to your final rendition. :thumbsup:

[Slawomir]

That's a fine image Andrew.

Yes, I was thinking of Ha/NII/OIII (I do not have SII for the Helix), but I feel that Luminance that simultaneously shows faint outer bows and also knots near the brighter centre will be the main challenge, to me anyway. Was hoping to collect RGB data for the stars last night, but unfortunately clouds rolled in and it looks like I will need to wait a bit for a clear night.

I look forward to seeing your image of the Helix Andrew.

If I was to attempt this target again, I would have gone with 30-minute subs instead of 15-minute subs, as now I have 373 15-minute subs across all three filters! :lol:

[Andy01]

Yes, I agree completely - It will be an interesting exercise in processing that's for sure. :question:



You can take a sneak peek at the first 15hrs of 3nm Ha data HERE (https://www.astrobin.com/full/363926/0/) - such a looong way to go to get sufficient data, given Melbourne's fickle weather, and I am doing it in 30mins subs :D

[Stevec35]

I agree with the comment about the colour being too pastel and the suggestion about adding RGB stars but overall I think that's a very nice result Suavi.

Steve

[Slawomir]

Your image of the Helix already looks very good Andy. It will be very interesting to see your interpretation of the Helix. My data processing skills are probably my greatest weakness in astro, so I am prepared for making numerous revisions until I reach the final image.

Thank you Steve for your feedback, it will help me greatly when I will make an attempt at putting all three channel together. Weather forecast predicts clearish night - I will be ready :)

[Bart]

That is very, very nice. Well managed and I like the colour so far.

[SimmoW]

Really deep and crisp there Suavi, and the noise controlled superbly so far. And you haven't been using Darks all this time? So your images will get even better?!

[Slawomir]

Thank you! Colours are not to everyone's taste but that's the nature of narrowband imaging :)




Thank you Simon. Well, it's not that simple with darks.

So far I have found that unless I have a very large number (more than 120 or so) of dithered subs, applying darks lowers the SNR.

For example, when stacking 120 dithered 15-minute OIII subs, SNR went slightly down for a stack of subs calibrated with darks, while for a stack of 165 dithered 15-minute Ha subs, SNR has very slightly improved when I applied darks in preprocessing.

My guess is that my camera adds only a tiny amount of fixed signal to 15-minute subs and mild dithering is sufficient to control it, and only stacking a lot of subs starts to bring up that signal to measurable levels.

In my recent project with the Helix, even extreme stretching to show faintest signal only 1ADU above the floor did not result in any noticeable glows nor banding in stacks that were calibrated without darks.

Here is an example of a bias-subtracted dark from my camera: https://www.astrobin.com/363774/?nc=user

Perhaps I could use many more darks than just 38 15-minute ones, but I'm not convinced that this will improve my data in a meaningful way.

[Atmos]

There was an interesting discussion on another forum recently about the SNR increases in a Master Dark as you increase the number of darks and 16 seemed to be pretty much the optimal amount between SNR and time put into darks.
Surprisingly the difference in SNR was only about 5% between 16 and 25 darks and as you also rightly point out, heavy dithering makes that further increase even more marginal.

[topheart]

Wow!, that is good Suavi!
Cheers,
Tim