NGC6960 - The Witches Broom

[steppenwolf]

Pretty moist conditions again tonight but clearer than I have had for some time so I had a go at the Witches Broom which is part of the Veil Nebula. I was keen to capture some of the more elusive green colouration tonight and succeeded to some extent!. 18 subframes of 300 seconds each with a Skywatcher 8" Newtonian and SXVF-M25C camera.

[Psychobilly]

Very nice Steve...

Nice to see you out and imaging again ... Lovely tracking focus colour and processing

What stacking method are you using as there is a hint of a satellite trail top left?

Peter...

[Beyond_Vision]

A lovely capture Steve it certainly is a beautiful object. I managed to see this one with my 12" Lightbridge last night with a UHC-s filter.

Regards

Kevin

[moocher]

Fabulous!!!

Alan:)

[steppenwolf]

What stacking method are you using as there is a hint of a satellite trail top left?

As this is such a relatively whispy object and I needed to extract as much from it as I could, I used the basic 'sum' method in MaximDL as I wanted to get on and process the image - if I had waited for SDMask (which would have resolved the hot pixel and satellite tracks somewhat) I'd still be waiting for the stack to complete!!!

[MartinB]

That's worked really well Steve. Were there any filters involved. I've always hesitated to use my QHY8 on emission line stuff, I found it pretty sluggish on the Horsehead last year but you've captured plenty here.

Did you have to do much work on the bright star? If you did then you've done a great job!

[steppenwolf]

Hi Martin,

The only filter I used was the IDAS LP filter which I consider a 'fixed' part of my imaging train. As I only have OSC cameras, I have no choice but to use them on emission objects but I find the M25C pretty responsive but, of course, I don'r have anything to compare it with on site! I did carry out a fair bit of post processing but I do this routinely anyway and I got the effect that I wanted by using several layers including one for just the green portion that I extracted using PhotoShop. The bright star is often problematic with this object but I think I took sufficient subs. to collect enough emission structure to combat the star with careful manipulation.

[RobH]

Very nice indeed Steve.

You've captured the wispy quality perfectly.

Cheers

Rob

[Aza]

Beautifully framed and processed.

The colours have been captured very well!

[Doc]

Oozes Quality.

[steppenwolf]

Thanks for comments folks - I must concentrate more on getting rid of satellite trails!

[roundycat]

what settings do you normally use for SD Mask? I think the default is three passes but if your sat trails are nor really noticeable in the first place one pass may well do the job and it will run like greased lightning.

Median is well worth a try as the difference in data 'loss' compared to SDM is minimal. Anything but Sum!!

Dennis

[steppenwolf]

Hi Dennis, I normally use 3 passes, Sigma Factor 3 as well. Thanks for the suggestion, I'll give that a try too.

Anything but Sum!!

You know, it's strange, sometimes I feel that Sum gives me the best result all round but it does vary from image to image.

[roundycat]

Steve, the sigma factor goes from quite small values to quite high but my reading of the way the algorithm works is that for the majority of decent sized stacks, ie, at least twenty, each pixel group will approximate to a normal distribution so anything above 3 sigma will effectively include all pixels in that group. The SDM algorithm will then give you an average for the output value. If you set the sigma factor lower then there is a much higher probability of the median value being used. This means that SDM tends to Median for low sigma values. Any outlier will be discarded regardless.

In the hundreds of tests I have done with these settings I have not been able to measure any meaningful difference. I usually go with sigma from 0.5 to 1 but there is no difference in the processing time.

Once the output from a Sum is scaled you are left with an average which tends to leave thousands of small pixel noise groups all over the place (which of course spread out if you dither). All that happens is they get fainter so with a small stack they are more obvious in the output.

Dennis

[Psychobilly]

Steve - I'll send you a sack of best Welsh Steam Coal for your computer

Peter...

[steppenwolf]

Thanks for that enlightenment, Dennis, very interesting and useful input!

That coal could come in handy, Peter although I am going to do a new stack tonight with Dennis' suggestion of a single pass in SD and a lower sigma value to see what results I get so the PC may be a little happier with the first bit!

[Tim]

It's a lovely shot Steve, but I think you will see a big improvement when it comes to processing when you go with SD Mask.

One of my favourites this, but like you, I've found it tough to get the OIII data with a OSC.

Cheers

Tim

[RichieJarvis]

Lovely capture Steve.... The focus is spot on, tracked perfectly, and full of detail. Glad to see you imaging again

I must say, I was surprised at your comment about taking so long to stack - until I remembered our conversation the other week about your steam powered computer

Although, saying that, once I grow up and get a proper size chip, I am sure I'll have the same problem!

Cheers,

Richie

[steppenwolf]

Hi Richie, the M25C doesn't help because of its relatively large sensor! For what it is worth, my PC has the following:-

AMD Athlon 64 3200+ 2.00GHz

1Gb RAM

Not exactly top stuff but it should be adequate, surely?

[RichieJarvis]

I think the best bet (and cheapest way forward) would be to up the RAM to 3GB - thats the max for Windows XP 32bit anyway - that will help alot, and is relatively cheap.

Good luck!

Richie

[daz]

Steve

That's the same chip I have in mine, and its no slouch, but you do need the RAM