Well, I think I can finally say I have reached the realms of diminishing returns on this target. I have now collected 111 hours of usable data. I have rejected about 28 hours of data in total, making total collected of 138 hours. Slight guiding errors, cloud and the moon being too close have been the main reason for rejection.
In the end I stacked the following:
60 hours in Ha
39 hours in OIII
12 hours in RGB (4 hours in each)
Some things I noticed as time went by.
1. The extra hours in RGB really worked well to show the star colour and smooth the image. I used lighten mode for the addition of the RGB and in several stages. Of interest is the galaxies that have shown up in the background. Whilst there are not hundreds there are a few more than you might expect. I have spent quite some time looking and deciding what is a faint star and what is a distant galaxy. A perfect example of integration have an effect.
2. Dithering becomes really important at this duration and I am going to reconsider my current dithering settings for future images. I noticed some fixed pattern noise appear over time despite dithering of at least 6 pixels. The Ha data I stacked 120 frames and so the dither was deficient for that many frames. Some subs were obviously overlapping.
3. Signal strength climbed slowly the point where some elements of the Helix look as solid as the central core. The outer reaches in particular took a lot of time to get to a point of solid definition and I suspect it would be a quite a lot of hours more to gain further definition and that gain would not be worth the extra hours. I added 29 odd hours to the previous version of this image and it took all that time to make the outer reaches appear more solid and brighter.
I think this image looks better than the previous version. I have cropped this image to remove a very bright flare from a star on the edge of the field, but essentially the full res image is at 100%.
Just had a fun half hour comparing the two versions. The main change seems to be a slight change in the colour, with the iris bluer and the eyebrow noticeably more magenta/red, less orange. The stars are a tad sharper, but I wonder if some of the faintest filigree in the nebulosity isn't sharper in the previous version.
Noise level is utterly negligible.
You've done a great job in maintaining the details in the cometary knots in the iris, showing the faintest outer features, and somehow, magically, maintaining the feel of their mutual relationship. Magnificent processing.
There's an orange-red blob at about ten o'clock which I'd often thought might be a face-on barred spiral - it has that look in just about everyone's shot - but you've convinced me it's actually nebulosity. I wonder if it's a part of the Helix or if it's just line of sight.
Another great megadata exercise Paul and as deep as I've ever seen the helix! It's amazing how 3D it now looks. One thing I noticed though is that the bright stars have dark centres in them. It's only a small point but I sometimes get told off when I do that.
Ah dammit, that's good! Slightly mesmerising - if I look into that eye long enough I'll be hypnotised by the great astro-deity Paul!
LOL, I seriously doubt that. Thanks for the compliment though.
Quote:
Originally Posted by RickS
Great job, Paul! As deep as I've seen...
Thanks Rick. Several dudes on CN seem to think otherwise. Funny reading some of the comments there. I think it is about as deep as an FSQ can go.
Quote:
Originally Posted by Placidus
That's pretty definitive.
Just had a fun half hour comparing the two versions. The main change seems to be a slight change in the colour, with the iris bluer and the eyebrow noticeably more magenta/red, less orange. The stars are a tad sharper, but I wonder if some of the faintest filigree in the nebulosity isn't sharper in the previous version.
Noise level is utterly negligible.
You've done a great job in maintaining the details in the cometary knots in the iris, showing the faintest outer features, and somehow, magically, maintaining the feel of their mutual relationship. Magnificent processing.
There's an orange-red blob at about ten o'clock which I'd often thought might be a face-on barred spiral - it has that look in just about everyone's shot - but you've convinced me it's actually nebulosity. I wonder if it's a part of the Helix or if it's just line of sight.
Thanks MnT. Maybe I sharpened some areas slightly differently this time and hence the different looking nebulosity. The cometary globules need to be reduced in brightness a lot as the data builds. The integration inevitably brightens that region right up to the point of being burnt out. I don't know what that blob is, but I think it is part of the nebula. I suppose it is possible to be completely separate and distinct from the nebulosity.
Quote:
Originally Posted by Stevec35
Another great megadata exercise Paul and as deep as I've ever seen the helix! It's amazing how 3D it now looks. One thing I noticed though is that the bright stars have dark centres in them. It's only a small point but I sometimes get told off when I do that.
Cheers
Steve
Thanks Steve, I think that might be a jpeg artefact with the stars. I just checked to see if there is any dots in the Tiff and there are none but I think I can see them on the web image. I did not apply any compression other than the format. Hmm not sure the cause.
I agree about the 3D look. Some of the processing tricks I use tend towards that look and more so with this vast volume of data. I have always wanted to create this sort of image for this object. It's such an interesting planetary.
Quote:
Originally Posted by AG Hybrid
Fantastic as usual. I suppose now you've reached the point where diminishing returns on exposure time are not providing enough usable data?
Thanks Adrian. The main thing I noticed in the last 10 hours of data was that there did not appear to be vast improvements on the signal. The noise in the Ha and OIII was fairly static too. I could easily go on and continue to collect data for another 20-30 hours before the season is over but I figure it would only be an experiment rather than for improving the image.
Top effort Paul: looks fantastic! It is incredible what a 4" scope can do.
Regarding the dark patches in the bright stars: I am wondering whether this is just a contrast effect: if you maximise them on screen and put a white mask around the star the "dark patch" is reduced considerably...
Wow! I love it, great detail around the blue area. I like points 1 & 2 you made, something to consider in the future. Star colours look great, and oh yeah...where do you find the time & clear skies, you seem to be pumping out a few images!
2. Dithering becomes really important at this duration and I am going to reconsider my current dithering settings for future images. I noticed some fixed pattern noise appear over time despite dithering of at least 6 pixels. The Ha data I stacked 120 frames and so the dither was deficient for that many frames. Some subs were obviously overlapping.
I have heard around this forum that sometimes the software dithers in a non random way, so regardless of what setting you use it will eventually image the same spot more than once. You may only be noticing it with really long exposures because it has time to accumulate in the average. You could try stacking with a different algorithm?
Congrats on your highest ever exposure. It'll stand as a record for some time (unless Rolf decides to do one!).
Nicely processed and a great look to it.
Greg.
Thanks Greg, its been epic, but no doubt Rolf is already planning an image of this target. Perhaps this might stand as a record for a 4" scope on this target. In any case, it was an exercise just to see what was really capable of being capture. Alas not much more if any more than other images of lesser data capture I think.
Quote:
Originally Posted by SkyWatch
Top effort Paul: looks fantastic! It is incredible what a 4" scope can do.
Regarding the dark patches in the bright stars: I am wondering whether this is just a contrast effect: if you maximise them on screen and put a white mask around the star the "dark patch" is reduced considerably...
Keep up the good work!
Dean
Thanks Dean, hmmm you could be right about the contrast effect.
Quote:
Originally Posted by E_ri_k
Wow! I love it, great detail around the blue area. I like points 1 & 2 you made, something to consider in the future. Star colours look great, and oh yeah...where do you find the time & clear skies, you seem to be pumping out a few images!
Erik
Thanks Erik, clear skies is a rarity but automation certainly makes the collection of data easy. I basically set an imaging run around late afternoon and then once it starts I take a look at the start and then the system takes care of the rest.
Quote:
Originally Posted by Peter.M
I have heard around this forum that sometimes the software dithers in a non random way, so regardless of what setting you use it will eventually image the same spot more than once. You may only be noticing it with really long exposures because it has time to accumulate in the average. You could try stacking with a different algorithm?
Thanks Pete, I tried three stacking algorithms. I tried mean, median and sum and each has the same results once I stretched the data. Although not entirely the same result, it was quite similar. Maybe I should try stacking stacks of say 20 and then stacking the resultant stacks. Perhaps the result will be different.
Quote:
Originally Posted by LewisM
Wow, 111 hours, and it's Sidonio Pink too
Impressive.
Thanks Lewis for the compliment.
Didn't know that the colour had been reserved. Though my aversion to magenta is not to do with the nebulosity but with the entire field having that particular cast or any other cast for that matter. Despite the fact that hydrogen is the most abundant element in the universe I doubt it exists in such volumes and is excited to the extent that it would create a magenta cast in all parts of the sky. Maybe I am wrong.
Slightly mesmerising - if I look into that eye long enough I'll be hypnotised by the great astro-deity Paul!
Though my aversion to magenta is not to do with the nebulosity but with the entire field having that particular cast or any other cast for that matter. Despite the fact that hydrogen is the most abundant element in the universe I doubt it exists in such volumes and is excited to the extent that it would create a magenta cast in all parts of the sky. Maybe I am wrong. 
