The Mystery of the Missing Cone Nebula in the Nighttime

[Knight of Clear Skies]

In February I had a go at shooting the Rosette and Cone region with my Samyang 135mm and modded 1100D. My run using the Ha filter come out pretty well but I also spent about 3 hours shooting in colour. I had a great deal of trouble stacking the data but finally managed after downloading the latest DSS, choosing 'bicubic' rather than 'automatic' as the alignment option and rejecting a few more subs. However, while I can see the Rosette I've tried stretching out the stack and can see nothing of the Cone region. This is bizarre, as I could just make it out in a 30 second framing shot.

I'm wondering what might have gone wrong and whether anyone has any suggestions please? A few vague ideas:

• Could the data be clipped somehow in DSS? I notice there is a 'set dark point' option ticked.
• Could the sigma clip be somehow destroying the faint nebulosity?
• I get very inconsistent results from DSS, sometimes the stacks are easy to process and other times they are an utter pain. Perhaps It's hiding in there but I'm just not processing it correctly.
• Were conditions worse than I thought with thin cirrus cloud obscuring the sky? Not that I remember.
• Could the lens have fogged up somehow? I think I remember checking it at the end of the run.

I've uploaded the autosaved stack from DSS to Dropbox if anyone would like a play with it. It's just stacked with dark bias as I my flats were over-correcting. I've also uploaded a single 2 minute sub.

Any help with this would be appreciated, I'd really like a colour version to put alongside the more detailed Ha portrait.

[Knight of Clear Skies]

Here's a two minute sub with a rough colour balance and quick run through Gradient Xterminator to get rid of the worst of the vignetting.

So the fainter nebulosity is definitely present in the subs.

[ollypenrice]

I think this is just a good demonstration of the value of the Ha filter. The camera is sensitive to Ha but it is the filter which excludes all but the Ha and finds the contrasts. I reckon you'll have a cracking result when you blend in the Ha.

Olly

[Knight of Clear Skies]

Thanks Olly but there is something else going on here - my stack appears to contain far less Ha signal than a single 2 minute sub!

I'm tempted to try blending the Ha in with a single RGB sub for the starfield.

[ollypenrice]

1 minute ago, Knight of Clear Skies said:

Thanks Olly but there is something else going on here - my stack appears to contain far less Ha signal than a single 2 minute sub!

I'm tempted to try blending the Ha in with a single RGB sub for the starfield.

Ah, gotcha. Very odd.

Olly

[tomato]

At the risk of stating what you already know, the Ha subs have plenty of signal so it must be the stacking process in DSS. Could you register all the subs then stack the channels separately in DSS then combine them with some other software, or is that your workflow already?

[Knight of Clear Skies]

On 07/04/2019 at 17:56, tomato said:

At the risk of stating what you already know, the Ha subs have plenty of signal so it must be the stacking process in DSS. Could you register all the subs then stack the channels separately in DSS then combine them with some other software, or is that your workflow already?

I shot it with a DSLR, so I don't think that's an option. I could try blending the Ha into the red channel of a colour starfield using Photoshop, I have done that once with partial success.

Would anyone be willing to take a quick look at the stack I attached to my first post please, to see if there is anything hiding in there? I often have trouble with the initial histogram adjustment in DSS.

[ollypenrice]

I know this is heresy but I can't say that I think much of DSS. I stack and calibrate in AstroArt which is far from expensive.

Olly

[Knight of Clear Skies]

Thanks, I'll take a look at the demo. DSS is great when it works but from time to time it gives me a stack which is a nightmare to colour balance, and I've had a lot of trouble applying flats as well.

I restacked sing the median option instead of a sigma clip and spent a lot more time trying to colour balance and stretch out the fainter detail. I'm finally getting somewhere, this is what I have so far.

Although as I couldn't get my flats to apply I suspect I may have nixed some of the nebulosity from the left of the image with GradEx. I'll play with this a bit more tomorrow and then see if I can blend in my Ha image into the red channel, using Photoshop.

[ollypenrice]

Looking very good. These very wide targets are never easy.

Olly