NGC 5139 Omega Centauri (Rod Kennedy)

NGC 5139 Omega Centauri

Omega Centauri is the sky's biggest and brightest globular star cluster and rises high in the sky here. It is easily visible naked eye even in the suburbs.

There was nothing too exceptional about the capture and processing. Perhaps the following are relevant:

* Deliberately very short exposures where used so that the core region didn't saturate.

* Only very minor post-processing was done in Photoshop.

* The Sento Senso motorised focuser and SGPro made focussing a joy. Focus is super important especially at the pixel scale used.

The pixels size on the 20M ZWO ASI183MM Pro being small at 2.4µm are near perfectly matched to the 431mm focal length of the WO ZenithStar 73 (Z73). If you do the math you see that more aperture doesn't give you better image resolution with good seeing at 2 arc secs. The Z73 is pretty fast at F5.9 and the ASI183MM (Sony IMX183CLK-J) is extremely sensitive (84% QE peak) so no bigger scope of similar or greater F-ratio gives any advantage.

There is a bit of redundancy in the equipment configuration.:

* The mount (yes it is not a typo) is for a much bigger telescope, needless to say wind was not a problem.

* The Z73 had a flattener to full frame but the sensor is only 13.2mm x 8.8mm. But remember we are already at 5496x3672 pixels (pictures are large) and you need to sample at round 2.4µm to match the optimal sampling for the seeing (neither under- or over-sampled).

* The cooler was on but not really needed. Same with having dark frames. I was just practicing for serious long exposure DSO down track. Flats still make sense because of dust but not because of vignetting (being well inside the flat field).

* The color guiding camera is one I had used for planetary work and is not a dedicated guiding camera. It was plenty sensitive enough even throwing away photons with its Bayer matrix.

Thanks for reading.

Original
B
Final
C

B

Description: Luminance filter stack image was used as a luminance layer in photoshop for this one which slightly improved the star shapes.

Uploaded: ...

C

Description: Darkened background

Uploaded: ...

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Status	Advanced success
Started	...
Astrometry.net job	3178607
PixInsight job	WA1WSXKIKXUK4LVJRRUXY8XNKEG3DGJ4
PixInsight queue size	n/a
PixInsight stage	n/a

RA (center)	13h26m50s.50
RA (top/left)	13h24m07s.80
RA (top/right)	13h24m35s.35
RA (bottom/right)	13h29m35s.58
RA (bottom/left)	13h29m01s.80

Dec (center)	-47°28′53″.2
Dec (top/left)	-46°52′55″.5
Dec (top/right)	-48°08′09″.4
Dec (bottom/right)	-48°04′36″.2
Dec (bottom/left)	-46°49′28″.1

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