Imaging the pacman and the lion. RGB plus NB

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timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Imaging the pacman and the lion. RGB plus NB

#1

Post by timh »

Continuing the theme of the last post - more images of smallish nebulae chosen as suitable targets for framing with a f = 1000mm Newtonian imaged with RGB + NB combinations as worked best.

In the case of NGC281 the RGB Ha image was clearly better than any RGB OOHa image that could be produced (not shown). Despite the fact that the O3 signal of this nebula is strong near the central star cluster it entirely coincides with Ha and there seemed no satisfactory way (luminance or colour channel) of adding in the 35x3 min of O3 signal without adding noise and/or decreasing the apparent resolution of small stars. So the additional time spent collecting NB O3 was wasted and the RGB (UHC) signal adequate to describe the location of the O3.

A new bit of learning - for NGC281 it was better to discard the RGB luminance altogether and simply replace it with the Ha signal. This led to the appearance of smaller and better resolved stars - cf the young (<3M years) central B1 multiple star - (but still with realistic colours) than by using the previous method of using a luminance signal derived from the maximum of both HA and RGB-L.

The lion nebula (Sh2-132) is too extensive to frame properly at f = 1000 mm. It was interesting though to see a separate and distinct area of blue-green OIII nebulosity (i.e where OIII outshines Ha) near the tail region (most of which was unfortunately out of frame) as well as some quite distinctly localised OIII banding within the 'head' region. Such strong OIII implies the presence of some very hot stars and indeed there are two Wolf Rayet stars---WR153ab (which may be a double pair?) and WR152 located just out of frame near the tail region. Because the Ha and OIII are not coincident it was more appropriate to image the Lion as RGB OOH - so here the luminance added back into the RGB signal was the overlayed maximum of the Ha and O3.

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SW200PDS Newtonian F5.0, Baader MkIII coma corrector, CEM70 mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, ASI 120 mm guide camera, Startravel80, f= 400mm guidescope

1) 110s exposures at gain 124 -10C with an ASI 1294 MC camera and Astronomik UHC filter under moonless Bortle 6 skies, 0.946 arcsec/pixel

2) 180s exposures at gain 151 -10C with an ASI 1294 MM camera and Optolong 7 nm HA filter and Bortle 6 skies. 0.946 arcsec/ pixel

3) 180s exposures at gain 151 -10C with an ASI 1294 MM camera and Astronimik 6 nm OIII filter under moonless Bortle 6 skies. 0.946 arcsec/ pixel

Capture using Sharpcap and FWHM / brightness filter. FWHM of individual frames 2.5 to 3.0. Guiding using PHD2 multistar, RGB frames preprocessed and stacked in PixInsight.

NGC281 (Pacman nebula) 48 x 110s (UHC), 35 x 3min (OIII) and 27 x 3 min (HA)

Sh2-132 (Lion nebula) 50 x 110s (UHC), 20 x 3min (OIII) and 20 x 3 min (HA)


The HA , OIII and RGB images were separately processed (noise reduction, background removal etc) and then, after stretching to non-linear. Here the RGB luminance was discarded altogether and replaced into the RGB image with either just the HA or with the maximum of the combined HA and O3 images. The resulting lumiunance-adjusted RGB image was was then adjusted using PI curves and tidied up using Affinity Photo and PhotoscapeX.






Tim
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aaa_pacman.JPG
aaa_pacman.JPG (102.67 KiB) Viewed 1408 times
aaa_lion.JPG
aaa_lion.JPG (181.13 KiB) Viewed 1408 times
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Menno555
Posts: 1053
Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
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Re: Imaging the pacman and the lion. RGB plus NB

#2

Post by Menno555 »

Always love your experiments and explanations Tim! :D
Over here there are simply not enough clear skies to experiment and that's kinda frustrating.

Menno
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