NGC6888 The Crescent Nebula in HOS

[TerryMcK]

I went over some old data that I took in August/September 2020 of the Crescent Nebula in my Bortle 7/8 skies with no real darkness. 

Telescope: William Optics ZS103 with x0.8 flattener/reducer

Camera: ZWO ASI183MM Mono

154 x Ha subs at 3 minute duration. Gain 111. Offset 8

90 x OIII subs at 3 minute duration. Gain 111. Offset 8

43 x SII subs at 3 minute duration. Gain 111. Offset 8

Processed as HOS with PixInsight and cropped.

 

I tried HSO and SHO but liked the HOS much more.

 

 

and below is my more recent processing with a slightly different technique - still using PixInsight no longer green OIII and a star reduction/erosion

 

[Stub Mandrel]

Loads of nice detail!

[peter shah]

That's a lovely rendition

[PeterBolt]

Amazing! ? 

[MarkAR]

Love it, The Crescent isn't easy to get right.

[TerryMcK]

Thanks all 🌜

[AstronomyUkraine]

On 2/3/2021 at 10:56 AM, TerryMcK said:

I went over some old data that I took in August/September 2020 of the Crescent Nebula in my Bortle 7/8 skies with no real darkness. 

Telescope: William Optics ZS103 with x0.8 flattener/reducer

Camera: ZWO ASI183MM Mono

154 x Ha subs at 3 minute duration. Gain 111. Offset 8

90 x OIII subs at 3 minute duration. Gain 111. Offset 8

43 x SII subs at 3 minute duration. Gain 111. Offset 8

Processed as HOS with PixInsight and cropped.

The HOS looks great, was wondering how you determined the gain and offset for the 183, they look very precise numbers.

Brian

[Jkulin]

Very nice Terry, I would personally just knock the green with the SCNR at 0.7: -

[TerryMcK]

2 hours ago, AstronomyUkraine said:

The HOS looks great, was wondering how you determined the gain and offset for the 183, they look very precise numbers.

Brian

They are the default values that ZWO set if you use their Windows driver or ASCOM driver. I replicated those values into the INDI driver. I’ve experimented with gain setting at higher values like 180 but that really results in too much amp glow for my liking. Halving the gain to 53 also is surprisingly good if you increase exposure slightly to compensate.

I have been using 111 and offset of 8 with longer exposures recently and getting fantastic results. The 183MM and 183MC are both seriously good cameras for the focal lengths I use. 

[TerryMcK]

2 hours ago, Jkulin said:

Very nice Terry, I would personally just knock the green with the SCNR at 0.7: -

Interesting results there John. It gives an ethereal glow to it.

[Jkulin]

Its lovely your image Terry and when I process my own as much as I love green I keep hearing in my head to remove it, but with your original it looked really good, but just wanted to see what it looked like with a reduction.

[AstronomyUkraine]

32 minutes ago, TerryMcK said:

They are the default values that ZWO set if you use their Windows driver or ASCOM driver. I replicated those values into the INDI driver. I’ve experimented with gain setting at higher values like 180 but that really results in too much amp glow for my liking. Halving the gain to 53 also is surprisingly good if you increase exposure slightly to compensate.

I have been using 111 and offset of 8 with longer exposures recently and getting fantastic results. The 183MM and 183MC are both seriously good cameras for the focal lengths I use. 

Intesting you use the windows driver. I have the 1600mm cool, it's not recommend to use the windows driver with SGP, but the Ascom driver instead. Using the windows driver in SGP allows you to change gain and offset automatically between sequences without going into the driver settings, and changing it manually, as you would with the Ascom driver.

Edited February 4, 2021 by AstronomyUkraine

[TerryMcK]

8 hours ago, AstronomyUkraine said:

Intesting you use the windows driver. I have the 1600mm cool, it's not recommend to use the windows driver with SGP, but the Ascom driver instead. Using the windows driver in SGP allows you to change gain and offset automatically between sequences without going into the driver settings, and changing it manually, as you would with the Ascom driver.

Sorry for the confusion. I don’t use the Windows nor ASCOM drivers at all as I no longer use the Windows operating system for image acquisition. I actually use the Linux based Raspberry PI4 with Astroberry/EKOS and that uses INDI which is similar to ASCOM. I just used the unity gain and default offset settings I saw when I used to use Windows/ASCOM and entered those into INDI. The parameters gain/offset are exactly the same in INDI as one would see in ASCOM.
EKOS (which is comprehensive sequencing software) also works just like SGP where gain and offset, amongst many other parameters, can be changed as you outlined.

 

Hope this makes sense.

[TerryMcK]

9 hours ago, Jkulin said:

Its lovely your image Terry and when I process my own as much as I love green I keep hearing in my head to remove it, but with your original it looked really good, but just wanted to see what it looked like with a reduction.

Yes I know what you mean John. Green can be a bit Marmite in astro photos but great that it can be toned down easily. I still have to learn the techniques how those greens can be changed to golds ala the most famous Hubble shots without looking plasticky. So much still to learn - so little new data with all these clouds 🙂

[AstronomyUkraine]

36 minutes ago, TerryMcK said:

Hope this makes sense.

Perfectly! I didn't realise that ZWO supported INDI. On their website I only see ASCOM or windows drivers.

[Jkulin]

1 hour ago, TerryMcK said:

Yes I know what you mean John. Green can be a bit Marmite in astro photos but great that it can be toned down easily. I still have to learn the techniques how those greens can be changed to golds ala the most famous Hubble shots without looking plasticky. So much still to learn - so little new data with all these clouds 🙂

It was very easy in Pixinsight using the SCNR tool.

 

ATB

[Gina]

Lovely colours 👍👍

[P Holdsworth]

Very nice image 👍

[TerryMcK]

I've done another rendition of the Crescent reducing the stars with erosion and star de-emphasis.

Processed entirely in PixInsight as CFHT which is the Canada-France-Hawaii Telescope Palette, assigning hydrogen to red, oxygen to green and sulphur to blue.

A bit more magenta than red in the Ha.

 

[AstronomyUkraine]

1 hour ago, TerryMcK said:

I've done another rendition of the Crescent reducing the stars with erosion and star de-emphasis.

Processed entirely in PixInsight as CHFT which is the Canada-France-Hawaii Telescope Palette, assigning hydrogen to red, oxygen to green and sulphur to blue.

A bit more magenta than red in the Ha.

This is an interesting combination. I think it can be renamed the rainbow Crescent. 😁

[gabs]

On 2/3/2021 at 8:56 AM, TerryMcK said:

I went over some old data that I took in August/September 2020 of the Crescent Nebula in my Bortle 7/8 skies with no real darkness. 

Telescope: William Optics ZS103 with x0.8 flattener/reducer

Camera: ZWO ASI183MM Mono

154 x Ha subs at 3 minute duration. Gain 111. Offset 8

90 x OIII subs at 3 minute duration. Gain 111. Offset 8

43 x SII subs at 3 minute duration. Gain 111. Offset 8

Processed as HOS with PixInsight and cropped.

 

I tried HSO and SHO but liked the HOS much more.

 

 

3 hours ago, TerryMcK said:

I've done another rendition of the Crescent reducing the stars with erosion and star de-emphasis.

Processed entirely in PixInsight as CHFT which is the Canada-France-Hawaii Telescope Palette, assigning hydrogen to red, oxygen to green and sulphur to blue.

A bit more magenta than red in the Ha.

 

Stupendo!! Wow

[PeterBolt]

Stunning 👏👏👏

[TerryMcK]

2 hours ago, AstronomyUkraine said:

This is an interesting combination. I think it can be renamed the rainbow Crescent. 😁

Good idea. I tried doing it in SHO using channel combo and didn't like the results so then I tried the more sort of traditional blend of Hubble with PixelMath to get the golds

// R:

.6*S2 + .4*Ha

 

// G:

.7*Ha + .3*O3

 

// B:

O3

 

 

I didn't like that either so back to HOS with equal blend just using channel combination and this is the result. I shall rename the process icon to Rainbow LOL

[AstronomyUkraine]

3 hours ago, TerryMcK said:

Good idea. I tried doing it in SHO using channel combo and didn't like the results so then I tried the more sort of traditional blend of Hubble with PixelMath to get the golds

// R:

.6*S2 + .4*Ha

 

// G:

.7*Ha + .3*O3

 

// B:

O3

 

 

I didn't like that either so back to HOS with equal blend just using channel combination and this is the result. I shall rename the process icon to Rainbow LOL

I use the exact formula for my SHO, but to get the gold colour, I also mix 50/50, or 60/40 with the dynamic formula used on the Coldest Nights website.

 

Sii/Ha/Oiii :

R = (Oiii^~Oiii)*Sii + ~(Oiii^~Oiii)*Ha

G = ((Oiii*Ha)^~(Oiii*Ha))*Ha + ~((Oiii*Ha)^~(Oiii*Ha))*Oiii

B = Oiii

 

The top image is the formula you use. The second image is the SHO formula mixed with the Coldest Nights formula. The second image was recently reworked image.

 

 

 

 

 

 

 

[TerryMcK]

Great tip Brian. I really must read the coldest nights website in greater detail. I saw it but skipped through the dynamic formula.