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Old 17-10-2021, 09:03 PM
Pilgrim (Igor)
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Helix nebula under Brisbane skies

NGC7293, perhaps my main object of this "winter", filmed almost every night during its visibility from the balcony. I also have good news that my new cooled mono camera finally arrived, so it's good time to finish and process all the long series I shot with Canon EOS-Ra to the moment.


Canon EOS-Ra DSLR on TAL-250K (10" Klevtsov-Cassegrain) with 0.7x flattner/reducer (NPZ MkII), mount Skywatcher EQ6R-Pro
Balcony in Brisbane (Toowong, Bortle-7 sky).

1359 x 1 min RGB
1285 min by 5 and 10 min subexposures with H-alpla filter (Antlia 3nm), mostly taken under the Moon
1000 min by 10 min subs with O-III filter (Antlia 3nm)

Total 3644 min (60 hours 44 minutes) of exposures taken during 32 nights in 2021:
31 of July, 04, 05, 06, 07, 11, 15, 16, 19, 21, 27, 28, 29 of August 06, 07, 08, 09, 10, 11, 13, 14, 14, 15, 16, 17, 22, 23, 24, 25, 02, 03, 04 of September.

Big image (click to zoom):

https://www.astrobin.com/full/q3eltn/0/

Starless image:
https://www.astrobin.com/full/q3eltn/D/


Stars was removed by Continuum Substraction method, residual artifacts was retouched in PS. not a single neural network was injured.

Software: APT, DSS, Iris, FITStacker, Photoshop
Attached Thumbnails
Click for full-size image (ngc7293_TAL250K_EOSRa_60h_HORGB_BNE_crop_size100_300Kb.jpg)
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Click for full-size image (ngc7293_TAL250K_EOSRa_60h_HORGB_BNE_size50_starless.jpg)
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  #2  
Old 18-10-2021, 08:32 AM
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PKay (Peter)
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A superb effort and result Igor.

One of the best I have seen.

I do prefer the stars left in and you can easily make out the small galaxies.

Very well done
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Old 18-10-2021, 08:47 AM
jahnpahwa (JP)
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Agree with PKay there. Great image, and the stars are beautiful., fun to find galaxies in the background.



Excellent to see an image out of a not-too-common OTA, too!
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Old 18-10-2021, 12:07 PM
AdamJL
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that's a beauty. I really love those galaxies hiding in the background as well!!
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Old 18-10-2021, 06:29 PM
Placidus (Mike and Trish)
Narrowing the band

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Absolutely excellent. There's a hint of one of the outer chevrons at far right. Love the rather large number of background galaxies showing form.



The super-ultra-long exposure was well worthwhile.
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Old 19-10-2021, 03:56 PM
topheart
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Well done!
Cheers,
Tim
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Old 20-10-2021, 12:26 PM
Pilgrim (Igor)
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Thank you so much, Peter, JP, Adam, Tim Mike and Trish!!!
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Old 20-10-2021, 12:36 PM
matlud (Mathew)
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A really great Helix -very nicely done 👍
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Old 20-10-2021, 12:40 PM
Dave882 (David)
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The full star version on a large screen is absolutely stunning!! Amazing work!!
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Old 20-10-2021, 02:06 PM
AdamJL
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Still coming back to this. It's so good. All the little galaxies in the background are beautifully brought out. That's when you know you've got a great image from light polluted skies.
Seriously well done, Igor.

Do you find any issues with using "mono" filters in front of a colour camera?
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Old 20-10-2021, 03:16 PM
JA
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It's incredible up close. Well done on a wonderful image Igor

Best
JA
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Old 20-10-2021, 04:47 PM
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Bassnut (Fred)
Narrowfield rules!

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Thats excellent Igor, especially for urban skies!.
Ive used a Continuum filter in the past for star removal and it works (in this case very well!), but these days starexterminator is way easier, no need for extra exposure time.
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Old 21-10-2021, 05:20 PM
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multiweb (Marc)
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Superb close up. I really like your gallery. Some terrific pics in there. That catadioptric of yours is giving you some great results.
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Old 22-10-2021, 11:00 AM
Pilgrim (Igor)
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Thank you for kind words, Mathew, David, Adam, JA, Fred and Marc!

Quote:
Originally Posted by Bassnut View Post
Thats excellent Igor, especially for urban skies!.
Ive used a Continuum filter in the past for star removal and it works (in this case very well!), but these days starexterminator is way easier, no need for extra exposure time.
The problem with algorithmic removal of stars (no matter neural networks or masks) is that while they work well for bright stars, they produce some artifact in border-condition stars and don't work for extremely faint barely-distinguishable background stars(which are a million times more).

The physical stars removal by subtraction of a continuum frame has the advantage that while giving some unwanted artifacts on bright stars,
it works good on medium, works well on weak and perfectly on an extremely faint indistinguishable "porridge" of background stars.

As a result, you get not only the removal of stars, but a much flatter, less noisy background, although you didn't even realize that part of its "noise" were groups of super weak indistinguishable stars barely leaked through the narrowband filter. Another bonus is that after retouching of artifacts, you can substract that starless H-alpha from the continuum image and this give you nearly perfect stars mask for future post-processing operations.

The closer an object is to the Milky Way, the stronger this effect is.
(It is a pity that there is a limitation, the method is suitable only for emission nebulae, in other cases there is no alternative to neural networks or masks-based wizardry.)
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Old 22-10-2021, 04:28 PM
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Bassnut (Fred)
Narrowfield rules!

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Quote:
Originally Posted by Pilgrim View Post
Thank you for kind words, Mathew, David, Adam, JA, Fred and Marc!



The problem with algorithmic removal of stars (no matter neural networks or masks) is that while they work well for bright stars, they produce some artifact in border-condition stars and don't work for extremely faint barely-distinguishable background stars(which are a million times more).

The physical stars removal by subtraction of a continuum frame has the advantage that while giving some unwanted artifacts on bright stars,
it works good on medium, works well on weak and perfectly on an extremely faint indistinguishable "porridge" of background stars.

As a result, you get not only the removal of stars, but a much flatter, less noisy background, although you didn't even realize that part of its "noise" were groups of super weak indistinguishable stars barely leaked through the narrowband filter. Another bonus is that after retouching of artifacts, you can substract that starless H-alpha from the continuum image and this give you nearly perfect stars mask for future post-processing operations.

The closer an object is to the Milky Way, the stronger this effect is.
(It is a pity that there is a limitation, the method is suitable only for emission nebulae, in other cases there is no alternative to neural networks or masks-based wizardry.)
All That you say is true, the continuum filter can be very effective...but. I often image 60 or more hrs with Ha for lum. I have found the continuum exposure time needs to be near or the same as the Ha image exposure for optimum results. Thats a hell of a lot of extra effort just for star removal !. I have found using that extra exposure time on data collection instead, and more fiddling in post to remove artifacts with software star removal gives a better final image. I do get your point though, a purist would go the extra mile for perfection without cheating .
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Old 24-10-2021, 09:41 AM
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Hi Igor,

That's a truly amazing image and shows the power
of stacking 1000s of frames.
Even with a DSLR camera you have still managed a great deal.


cheers
Allan
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  #17  
Old 01-11-2021, 06:27 PM
Addos (Adam)
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very nicely done! showing us that good equipment blended with good technique yields pretty darn good results even in nasty light pollution!

august / september in bris once the milky way core gets low in the sky is really all about the helix isnt it well that and the tarantula. pretty dry otherwise nebula wise

this 3 week never ending clouds thing is getting old though. and just when orion region is starting to rise early enough to be worth it
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