NGC6820 - finally a bit of data

[gorann]

Astrodarkness is getting back up here. This is the first decently large data set I got with my new ASI071mcc pro, almost 6 hours over the last two nights, but with a half moon. First night I managed to get 29 x 3 min of RGB data (gain 150 offset 20) and the second night I put on a Ha fliter and got 52 x 5 min Ha data (gain 200 offset 20). So Ha through a OSC.... yes I know it is not optimal but it has 16 megapixels and is quite sensitive with low noise and what do you do if they do not sell APS-C sized mono CMOS cameras (yet). Chip at -15°C. Stacked and calibrated in PI. Processed in PS. This is a fairly faint object so obviously more data would be nice. But I think it is a very promising camera.

Comments and suggestions most welcome!

[Adreneline]

This is a new one for me. I need to see if this target is in a bit of sky I can see - or whether it's behind the house! Arghh!

The Ha-osc combination seems to have worked very well.

Thanks for sharing.

[wimvb]

Congratulations on a double successfull first light: camera and scope.

Now you just need to learn how to create that black border in PixInsight. ? (spoiler: it's easier than you'd think)

[drjolo]

It is faint object indeed - I imaged it once with modded DSLR for 11 hours, and the outcome was a little bit disappointing. I think for OSC cameras it is hard to capture photons with Moon present (without Ha filter). Maybe the overall frame is a bit too red, but quite a lot of detail was recorded. 

PS - I also miss larger mono CMOS sensors  

[Cozzy]

Yes that is a great image.

there is a lot of data yet to pull out, IMHO you could try to lift the mid tones, lighten a touch, a bit of contrast and push the red over to the blue slightly to reduce that red a bit. just my opinion.

Tim

[gorann]

3 hours ago, Adreneline said:

This is a new one for me. I need to see if this target is in a bit of sky I can see - or whether it's behind the house! Arghh!

The Ha-osc combination seems to have worked very well.

Thanks for sharing.

 

2 hours ago, wimvb said:

Congratulations on a double successfull first light: camera and scope.

Now you just need to learn how to create that black border in PixInsight. ? (spoiler: it's easier than you'd think)

 

2 hours ago, drjolo said:

It is faint object indeed - I imaged it once with modded DSLR for 11 hours, and the outcome was a little bit disappointing. I think for OSC cameras it is hard to capture photons with Moon present (without Ha filter). Maybe the overall frame is a bit too red, but quite a lot of detail was recorded. 

PS - I also miss larger mono CMOS sensors  

 

1 hour ago, Cozzy said:

Yes that is a great image.

there is a lot of data yet to pull out, IMHO you could try to lift the mid tones, lighten a touch, a bit of contrast and push the red over to the blue slightly to reduce that red a bit. just my opinion.

Tim

Thank you all!

Before I read you comments I had already made a second version. Maybe a bit more in Tims taste?

[gorann]

With the rather strong stretches I had to apply to this faint object there was some apparent banding noise and amp glow on top and bottom, even if I used darks. Wim now told me of the PI script called Canon Banding Reduction, which actually worked fine for both the banding and amp glow, although it introduced some artefacts so I applied it selectively using layer masks in PS). So here is a version that I think is the best so far. Also worked a bit on colour and contrast. Another conclusion is probably that 10 min exposures rather than 5 min would be better for such weak Ha at gain 200.

 

 

 

[gorann]

For the record. Here is the final version where I brought out as much dust as possible, suppressed red blotches in the background, and had a go at deconvolution in PI to sharpen the stars. Since there has been no clear skies I have been messing with this one for too long now.

[ollypenrice]

My feeling about targets like this, which I think Gorann has done very well indeed, is that they are difficult because the nebulosity has only one colour dimension - red - from the Ha. To redress this colour dimensional problem we need either a different narrowband source or very deep LRGB and extremely strong star colour. This isn't a criticism of Gorann's image, it's a reflection on the relationship between certain targets and the equipment which is available to us.

Olly

[gorann]

18 minutes ago, ollypenrice said:

My feeling about targets like this, which I think Gorann has done very well indeed, is that they are difficult because the nebulosity has only one colour dimension - red - from the Ha. To redress this colour dimensional problem we need either a different narrowband source or very deep LRGB and extremely strong star colour. This isn't a criticism of Gorann's image, it's a reflection on the relationship between certain targets and the equipment which is available to us.

Olly

Thanks Olly. Yes, what is suffering in the image is colour in the smaller stars and I just need more RGB data for that. Not sure if there is much Oiii in this object that could help. In any case this is for another time with clear skies of which I have none right now. I still I think that the image shows that it is possible (but obviously not ideal) to collect Ha with these new CMOS OSCs - the 52 x 5 min of Ha is what brought out all the details in the image.

[wimvb]

2 hours ago, gorann said:

Not sure if there is much Oiii in this object that could help

This is actually a very interesting nb target:

http://www.astronomersdoitinthedark.com/index.php?c=183&p=592

Btw, I think I prefer the previous version. On my mobile device, the weaker areas seem to show a little more definition. Haven't looked at it on my laptop yet.

Edit: On my laptop the latest version looks better. Btw, I think you should test ACDNR noise reduction in PI on chrominance only. Try it with an inverted lightness mask at the very end of the process. It's very good at killing chrominance noise from osc cameras.

[gorann]

9 hours ago, wimvb said:

This is actually a very interesting nb target:

http://www.astronomersdoitinthedark.com/index.php?c=183&p=592

Btw, I think I prefer the previous version. On my mobile device, the weaker areas seem to show a little more definition. Haven't looked at it on my laptop yet.

Edit: On my laptop the latest version looks better. Btw, I think you should test ACDNR noise reduction in PI on chrominance only. Try it with an inverted lightness mask at the very end of the process. It's very good at killing chrominance noise from osc cameras.

Thanks Wim - will try and it gives me something to do on this rainy Sunday,

[tooth_dr]

I agree the latest version looks much more pleasing. 

On 05/09/2018 at 10:48, gorann said:

With the rather strong stretches I had to apply to this faint object there was some apparent banding noise and amp glow on top and bottom, even if I used darks. 

Interesting, I’ve been stretching my DSLR data quite hard recently and for the first time I’ve noticed broad colour banding across it the image. Is this what you were experiencing?

[gorann]

On 09/09/2018 at 09:20, tooth_dr said:

I agree the latest version looks much more pleasing. 

Interesting, I’ve been stretching my DSLR data quite hard recently and for the first time I’ve noticed broad colour banding across it the image. Is this what you were experiencing?

Thanks Alan!

Yes, it was broad bands at least in the Ha data. Here I have "overstretched" the Ha data to emphasize the banding (First Image). Attacking it with Horizontal Banding Noise Reduction (Noel's Actions) in PS had no effect (but I know it to work fine for more narrow banding) (Second Image). However Canon Banding Reduction in PI did a very good job at removing them so as long as that works this banding is no big problem (Third Image). I know Wim @wimvbwill have a field day now when I admit that certain things work better in PI than in PS.

[wimvb]

Since the camera is osc, even the Ha is colour. You can convert it to gray scale in two ways: 1. Extract luminance or 2. Extract the red channel. To me, the second option makes more sense. Since green and blue pixels don't contain any signal , but only dark current and read pattern noise, the banding may originate from these. The red channel is the only one containing pure data. And this turned out to be banding free(*).

No banding, no need for CBR. And no artefacts introduced.

(*) Göran kindly provided me with the Ha master.

[gorann]

6 hours ago, wimvb said:

Since the camera is osc, even the Ha is colour. You can convert it to gray scale in two ways: 1. Extract luminance or 2. Extract the red channel. To me, the second option makes more sense. Since green and blue pixels don't contain any signal , but only dark current and read pattern noise, the banding may originate from these. The red channel is the only one containing pure data. And this turned out to be banding free(*).

No banding, no need for CBR. And no artefacts introduced.

(*) Göran kindly provided me with the Ha master.

Interesting. I turned it into grayscale in PS. Will try to do it your way in PS next time Wim.