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Author Topic: Bortal 8+ Imaging from West London  (Read 8092 times)

oliverthom707

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Re: Bortal 8+ Imaging from West London
« Reply #45 on: July 15, 2020, 07:06:56 pm »
Nice images, especially considering your Bortle zone. Thanks for sharing!

susan-parker

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Re: Bortal 8+ Imaging from West London
« Reply #46 on: July 18, 2020, 05:03:28 pm »
Thanks Vince and Oliver :)

At last some clearer skies last night and an opportunity to catch 188 more Hydrogen-alpha frames to add to my M16 Eagle Nebula image campaign.

There is noticeably more details in the dark filaments in the nebula regions.

This one is nominally using the Hubble Pallet (Ha assigned to the green channel), although I have SII and OIII frames most of the information is in the Ha.

1 to 1 pixel crop, with stars down to magnitude 16.

susan-parker

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Re: Bortal 8+ Imaging from West London
« Reply #47 on: July 23, 2020, 12:23:07 pm »
M24 Small Sagittarius Star Cloud with dark nebulae Barnard 92 & 93 prominent, IC1284 HII region in centre of frame, additional Ha regions clearly visible.

Positions of the NGC6603 open star cluster and NGC 6567 Planetary Nebula just visible.

Session was an opportunity grab starting at 11 p.m. BST, through increasing to 20%+ cloud cover as the session progressed.

Atik 7nm narrowband Ha, SII and OIII filters (with Ha on red channel); 40 frames of 30 seconds each per channel, Atik Horizon with Dusk for capture, sensor at -15°C, High Gain (30x).

N.B. I have had to crunch the JPEG quality down to get under the 600K limit although the original is not unexpectedly rather noisy as well as busy with stars.
« Last Edit: July 23, 2020, 07:17:57 pm by susan-parker »

susan-parker

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Re: Bortal 8+ Imaging from West London
« Reply #48 on: July 25, 2020, 06:33:49 pm »
M24 Small Sagittarius Star Cloud campaign update:

I got a chance to shoot a few more Ha frames last night in between the thicker clouds, and got 138 usable frames out of 238 taken.

So I now have 178 Ha frames, 40 SII, and 40 OIII in total, each 30 seconds exposure.

This is still through varying light cloud and background light pollution, but the added Ha really makes a difference. The image looks less punchy but that is from increased background presence. The black in Barnard 92 really is black, just little else in the frame is!!!

CraigG

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Re: Bortal 8+ Imaging from West London
« Reply #49 on: July 26, 2020, 04:09:29 pm »
Nice enhancement Susan. You've inspired me to check out M24 myself. How much do you think the SII channel contributed to your final image? I'm thinking about adding that filter to my toolbox.

Thanks!
-Craig

vince

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Re: Bortal 8+ Imaging from West London
« Reply #50 on: July 27, 2020, 11:46:58 am »
That's looking good Susan.

Vince :)

susan-parker

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Re: Bortal 8+ Imaging from West London
« Reply #51 on: July 27, 2020, 05:50:25 pm »
Hi Craig,

I am still relatively new to NB filter imaging, only got my filter-wheel working at end of February.

The M24 image is apparently a predominantly Hydrogen emission region, what I think I am seeing is that for more conventional nebula targets e.g. Orion Nebula, the normal practise seems to be to back off the Ha as it is a lot brighter than the other two SII and OIII channels to get a pleasing 3 colour RGB image, but this technique applied here would understate the Ha line.

In the M24 area the three filters are narrow-band filtering the normal range of "white" light plus any emission lines.

This image is the Ha 656nm as red with the SII 672nm (green) subtracted. These 7nm filters are very close together so it is reasonable to assume that the camera sensitivity and filter characteristics are similar enough to treat them as equal as far as "white" light is concerned, and therefore taking away the SII filter channel will leave the Ha. If there is some SII then that would be subtracted too, so the assumptions as to the Ha remain sufficiently valid since it is a lesser crime to underreport in this instance :)

The background mottling is from the much fewer SII frames (40) compared to the Ha (178) frames.

The stars down into magnitude 12 have been made blue to contrast with the red.

There seems to be a fair amount of Ha emission going on, above and beyond the background "white" light.

Perhaps someone more knowledgable would care to comment?

For other targets, a SII filter would be directly contributing to the final RGB image.

For fun, look at the human eye response, the Red and Green cones are shockingly close together compared to the blue:

E.g. https://upload.wikimedia.org/wikipedia/commons/3/32/Opsin_Absorption_Spectra.png

... then compare to a colour camera's coloured matrix filter which is much more evenly spaced.

Best,
Susan.

BTW Thanks Vince :)

CraigG

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Re: Bortal 8+ Imaging from West London
« Reply #52 on: July 28, 2020, 01:30:54 pm »
Hello Susan,

Thanks for the great info on your M24 image and for your analysis of the Ha/SII relationship in general. The absorption spectra angle/OSC matrix comparison is an interesting side note. I'm very impressed with your understanding of narrowband components and how they apply to astrophotography. I hope to one day at least approach the level of knowledge that you possess on the subject! As I'm also relatively new to the art of NB imaging, I look forward to your future posts. This forum has lots more potential for sharing details of image acquisition and best practices in a bit slower paced environment than say Astrobin, etc. Hopefully that activity will increase as time goes on! :)

Best wishes,
Craig

susan-parker

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Re: Bortal 8+ Imaging from West London
« Reply #53 on: July 31, 2020, 07:15:19 pm »
Messier M17 - The Omega Nebula in Sagittarius (aka the Swan Nebula) taken last night is poor seeing conditions

There was thin high cloud and the 85% moon was pretty bright and only 10 degrees off the field of view, so a lot of background noise (above and beyond the normal Bortle 8+ stuff).

The Messier M18 open cluster of stars is also present albeit not as dramatic towards the lower-centre of the image.

60 frames of 30 seconds each for each of the 7nm narrow-band Ha SII OIII filters.

This image is a crop of the full-frame at 50% scale.


susan-parker

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Re: Bortal 8+ Imaging from West London
« Reply #54 on: July 31, 2020, 07:23:53 pm »
Hi Craig,

Thanks. Part of this is putting in a lot of time making multiple stabs at the processing. What works well for one image does not always give such good results for another, there is always tweaking and optimizing (as well as going back and redoing from scratch).

Further to the filter thing; here is an image of M17 showing the RGB breakdown by the separate narrow-band filters.

As can be seen for M17 there is substantial nebula emissions on all three channels; whereas for the previous M24 image most of that area was just Hydrogen-alpha.

The Atik 7nm bandwidth filters are definitely earning their keep at cutting down on the background light.

susan-parker

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Re: Bortal 8+ Imaging from West London
« Reply #55 on: August 01, 2020, 12:29:12 pm »
This is a quick-look mosaic of last month's narrow-band nebula campaigns, with my targets in bold.

Top to bottom:
Sharpless 2-54 Nebula
Messier M16 Eagle Nebula
Messier M17 Omega/Swan Nebula
Messier M18 Open Star Cluster
Messier M24 Small Sagittarius Star Cloud
IC-1283 Nebula
μ Sagittarius (Polis) Blue Supergiant Star (mag 3.86)

The three overlapped images represent approximately 10° of the sky in height.
The unscaled image is 4500 x 11500 pixels in size.