RGBHa of Elephants trunk at f = 1000 and f = 616 mm

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timh
Posts: 311
Joined: Mon Aug 26, 2019 5:50 pm

RGBHa of Elephants trunk at f = 1000 and f = 616 mm

#1

Post by timh »

110 mm Apochromatic William Optic Zenithstar F 7,0 refractor, William FLATIII 0.8X reducer flattener (to f = 616 mm and F 5.6), CEM 70 Ioptron mount Moonlite focuser and controller. PHD2 guiding using an ASI 120 mm guide camera and 80 mm SW startravel refractor at f = 400 mm.

SW200PDS Newtonian (f = 1000mm, F5.0) Baader MkIII coma corrector, CEM70 Ioptron mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, PHD2 guiding using an ASI 120 mm guide camera and 80 mm SW startravel refractor at f = 400 mm.

ZWO AS1294 MC camera for RGB (UHC) captures or ZWO ASI294MM mono camera for HA , both 4.63 uM pixels cooled to -10C

ZWO IR/UV cut filter, Astronomik UHC filter. Optolong HA 7 nm filter

All frames captured between 28'th August and 11'th October.

UHC frames captured under under moonless Bortle 6 skies, HA frames captured with the moon risen but low in the sky and far from IC1396 which was near the zenith.

All frames pre-selected for quality using SC FWHM filter and then (pass rate 40-80%) PixInsight Blink and Subframe Selector tools.

Captures with Sharpcap and then preprocessing plus processing in PixInsight.

I found processing images of the Elephants trunk (IC1396A) to be quite difficult and it took some time.

One problem is that the object is much bigger than either of my telescopes could frame. This means that you can run into trouble if you try to use any of PI's background subtraction tools (DBE and ABE) - a frequently used first step - because applying any sort of arbitrary initial subtraction seemed to lead to eventual colour distortion.

In the end a 'less is more' approach to image processing seemed to work best ...the processing tools used were photometric colour calibration, star mask/ size reduction, noise reduction and curves. The object presents many choices in terms of how it should best be represented. I again went for using the HA as luminosity (once again O3 was coincident and added nothing over HA) which, as well as better detailing the nebulosity also minimizes the stars and limits bloating.

Overall I think that the object framing is better suited to the refractor (1.55 AS/ pixel) - and ideally an even shorter focal length - but that the longer focus Newtonian (0.95 AS/ pixel) does resolve a bit more detail in the closer up image. However the colour of the Newtonian image is a bit washed out because I wasn't able to accumulate enough good quality RGB frames relative to HA.

Image 1. Zenithstar 110 mm refractor f = 616mm. 133 x 110s exposures (UHC filter) at gain 124, pixintegration, with luminance from 35 x 3 min exposures (HA filter) at gain 151

Image 2. SW 200PDS newtonian f = 1000 mm, 43 x 110s exposures (UHC filter) at gain 124, pixintegration (debayer), with luminance from 70 x 3min exposures (HA filter) at gain 151

Tim
Attachments
aaaIC1396_Zstar.jpg
aaaIC1396_Zstar.jpg (962.51 KiB) Viewed 366 times
aaaIC1396_Newt_Baader_060921_UHC_43_selected_x110s_gain124_CROP_PCC_strmask_MLT_TRANS__lum__71x3minHA_gain151_2508__curves_PX.jpg
aaaIC1396_Newt_Baader_060921_UHC_43_selected_x110s_gain124_CROP_PCC_strmask_MLT_TRANS__lum__71x3minHA_gain151_2508__curves_PX.jpg (950.17 KiB) Viewed 366 times
Last edited by timh on Wed Dec 08, 2021 8:36 pm, edited 1 time in total.
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Menno555
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Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
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Re: RGBHa of Elephants trunk at f = 1000 and f = 616 mm

#2

Post by Menno555 »

Great captures Tim! I like the 2nd one a lot, the contrast does a lot there.
And yes, I did find the Elephant Trunk also difficult to process. It really was a balancing game to get details without overstretching. It's always a balance ofcourse but with this it was really harder

Menno
timh
Posts: 311
Joined: Mon Aug 26, 2019 5:50 pm

Re: RGBHa of Elephants trunk at f = 1000 and f = 616 mm

#3

Post by timh »

Many thanks Menno. Working on processing old stuff at the moment since the weather has permiited so few opportunities this past month or so - expect that it is similar in the Netherlands?

Tim
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Menno555
Posts: 599
Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
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Re: RGBHa of Elephants trunk at f = 1000 and f = 616 mm

#4

Post by Menno555 »

Oh man, it's terrible here :( There were a few hours on 22 November (with of course an almost full moon), a few hours on 25 October ... and long term predictions are all in the red also.
I really can understand more and more that people give it up out of frustration. I won't of course ;)

Menno
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