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.
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.
Quote:
Originally Posted by gregbradley
I like the extra details you brought out but it seems to have lost colour saturation in the process.
Greg.
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.
Quote:
Originally Posted by Atmos
Those fainter areas are showing up really well Suavi
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 :-)
Quote:
Originally Posted by Retrograde
Great result Suavi. Love seeing those faint outer shock-fronts.
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.
Quote:
Originally Posted by Placidus
The new stretch is simply stunning.
A magnificent result.
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.
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.
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...
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.
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.
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!
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!
but I feel that Luminance that simultaneously shows faint outer bows and also knots near the brighter centre will be the main challenge...
Yes, I agree completely - It will be an interesting exercise in processing that's for sure.
Quote:
Originally Posted by Slawomir
I look forward to seeing your image of the Helix Andrew.
You can take a sneak peek at the first 15hrs of 3nm Ha data HERE - such a looong way to go to get sufficient data, given Melbourne's fickle weather, and I am doing it in 30mins subs
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.
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
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?!
That is very, very nice. Well managed and I like the colour so far.
Thank you! Colours are not to everyone's taste but that's the nature of narrowband imaging
Quote:
Originally Posted by 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?!
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.
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.
