NGC 7293 Helix Nebula under City Suburban Skies

[strongmanmike (Michael)]

Originally Posted by Startrek

Thanks Mike for comments and comparisons
Much appreciated
Newcastle back in 2002 was probably a Bortle 6 compared to Sydney in 2024 at Bortle 8 to 9 , only a guess by the way
Next time your in Sydney take a drive along Canterbury road around Petersham and look up at the night sky , you’ll wonder why we bother imaging.
My LP reading is 18.22 mag/arcsec2 and getting worse each year
I’ve tried 5min subs on the Dolphin a while back and the noise floor was still fairly high which inhibited me from stretching too far to expose fine detail.
Catch 22 scenarios

Cheers
Martin

All valid factors I guess, oh and my data was from 2011, taken from the suburb of New Lambton, so yes, in 2015 it was Bortle 6, probably Bortle 7 by now..?

Mike

[AlexN]

Martin,

Here's the foraxx blend of mine - 200x600s (33hrs 20min) subs now with an 65mm f/6.4, IMX294 and 6nm Ha/OIII dual band filter.

Dithered every 5 frames, 2x drizzle, sharpening applied at 2x then resized down to original resolution (This is a 100% crop from my full image)

Adding more exposure now is helping with noise, but I'm not resolving anything finer than the detail that's already present I don't think...

With your background noise - I used to have a similar issue when I was running too low of an offset value - the darker detail was being lost at the very bottom of the histogram and I wasn't really able to pull it out without also draging the noise up with it. I went from an offset of 25 to an offset of 60 and now darker details are becoming visible in relatively short integrations, longer integrations are allowing me to reveal very dim structures, even in OIII data...

Alex

[CaptainCook (Gary)]

Attached are two figures from CR O'Dell et al 2004 "Unravelling the helix nebula: its structure and knots'', which analysed Hubble and ground based images, together my starless Ha as a comparison of what you are able to get from B7 Sydney. I am seeing all of these features after a few hours using a 6nm Ha filter and 300s subs- with the exception of the NE shockwave. Doubling integration time to 11 hours made no difference but the SNR helped reduce the background artefacts a bit more.

[Startrek (Martin)]

Originally Posted by AlexN

Martin,

Here's the foraxx blend of mine - 200x600s (33hrs 20min) subs now with an 65mm f/6.4, IMX294 and 6nm Ha/OIII dual band filter.

Dithered every 5 frames, 2x drizzle, sharpening applied at 2x then resized down to original resolution (This is a 100% crop from my full image)

Adding more exposure now is helping with noise, but I'm not resolving anything finer than the detail that's already present I don't think...

With your background noise - I used to have a similar issue when I was running too low of an offset value - the darker detail was being lost at the very bottom of the histogram and I wasn't really able to pull it out without also draging the noise up with it. I went from an offset of 25 to an offset of 60 and now darker details are becoming visible in relatively short integrations, longer integrations are allowing me to reveal very dim structures, even in OIII data...

Alex

Alex,
That’s a fine Helix , well done !
I dither every sub as my settle time in PHD2 / APT is only 12sec
My problem is I’m looking at too many Helix images on Astrobin under super dark skies with mammoth hours +40. I’ve captured some more Ha last night and tonight so will process just Ha and see how much more detail can be pulled out without crashing the image.
My offset of 50 for the 2600MM at Gain 0 and Gain 100 HCG is fine and recommended by ZWO.

Cheers
Martin

[Startrek (Martin)]

Originally Posted by CaptainCook

Attached are two figures from CR O'Dell et al 2004 "Unravelling the helix nebula: its structure and knots'', which analysed Hubble and ground based images, together my starless Ha as a comparison of what you are able to get from B7 Sydney. I am seeing all of these features after a few hours using a 6nm Ha filter and 300s subs- with the exception of the NE shockwave. Doubling integration time to 11 hours made no difference but the SNR helped reduce the background artefacts a bit more.

Thanks Gary,
Yeh it’s a hard one this Helix as with most faint targets under heavy LP.
I’ve captured more Ha last night and tonight , so when I get some time I’ll process a new version just in Ha and see how it compares.
Cheers
Martin

[gb44 (Glenn)]

Could a tweak in post-processing help...I just found a function in SIRIL where
one can highlight a region of interest within the generalised hyperbolic stretch and manipulate that region - increasing its stretch and contrast. The method is to draw a box on the ROI and then click on the eyedropper of the symmetry point slider. Stretch and increase the local stretch intensity to effect.

Surely with the data you have you may well have the desired look anyways.

GlennB

[Startrek (Martin)]

Originally Posted by gb44

Could a tweak in post-processing help...I just found a function in SIRIL where
one can highlight a region of interest within the generalised hyperbolic stretch and manipulate that region - increasing its stretch and contrast. The method is to draw a box on the ROI and then click on the eyedropper of the symmetry point slider. Stretch and increase the local stretch intensity to effect.

Surely with the data you have you may well have the desired look anyways.

GlennB

Thanks Glenn,
Appreciate your input
I use Startools which has AutoDev as your global stretch where you draw a ROI around your object, adjust this ROI and it automatically and mathematically finds a starting point to commence adjusting parameters to taste.
Very powerful tool
Have a read if you have time

https://www.startools.org/modules/autodev

Martin