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Spiral Galaxy NGC 6744 in Pavo

NGC 6744 is a Milky Way like barred spiral galaxy in the constellation Pavo.  Visible only from lower latitudes, the light we see now left this galaxy around 25 million years ago. 

554CC5C5-67D9-4D25-A093-9F10D39C9E5A.thumb.jpeg.8eda5b710d2028e8452629ff6ceb1898.jpeg

NGC 6744 in Pavo ( please click / tap on image to see larger and sharper )

 

Capture Details:

North is up.

Telescope: 
Orion Optics CT12 Newtonian ( mirror 300mm, fl 1200mm, f4 ).
Corrector: ASA 2" Coma Corrector Quattro 1.175x.
Effective Focal Length / Aperture : 1400mm f4.7.

Mount: 
Skywatcher EQ8.
Guiding: TSOAG9 Off-Axis-Guider, 
Starlight Xpress Lodestar X2, 
PHD2 .

Camera:
Nikon D5300 (unmodified) 
(sensor 23.5 x 15.6mm, 6016x4016 3.9um pixels).

Location:
Blue Mountains, Australia 
Moderate light pollution 
( pale green zone on darksitefinder.com map ).

Capture ( 16, 17, 19 Sept. 2017 ).
9 sets of sub-images with exposure duration for each set doubling ( 1s to 240s ) all at ISO800.
85 x 240s + 5 each @ 1s to 120s.

Processing ( Pixinsight - 5-17 Nov 2017  ).
Calibration: master bias, master flat and no darks.
Integration in 9 sets.
HDR combination 
PhotometricColorCalibration
Arcsinh stretch ( function written by Mark Shelley )

Image Plate Solver - NGC 6744 - Sept 17, 2017
===================================
Resolution ........ 0.586 arcsec/px ( full size image )
Rotation ............ 0.001 deg.
Focal ................. 1372.24 mm.
Pixel size ........ ..3.90 um.
Field of view ..... 58' 30.3" x 38' 59.0".
Image center ...... RA: 19 09 46.591  Dec: -63 51 13.44
==================================

        

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The new Pixinsight Arcsinh stretch function ( written by Mark Shelley ) was used to stretch the HDR linear image whilst keeping colour in the stars.  Thanks Mark :icon_salut:

 

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13 hours ago, Victor Boesen said:

Beautiful image!!!

 

12 hours ago, cfpendock said:

Very nice image.  Sadly this one is not available here....

Chrid

 

6 hours ago, joelshort said:

Very nice!  I really like the new ArcsinStretch too.  It works really well on RGB data.

Thanks guys, much appreciated.

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Very nice, not one I am familiar with. What’s the benefit of the range of 1s exposures from 1-120s?

Thanks

Adam. 

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7 minutes ago, tooth_dr said:

Very nice, not one I am familiar with. What’s the benefit of the range of 1s exposures from 1-120s?

Thanks

Adam. 

Thanks Adam - NGC 6744 is way down here in the South and is a little compensation for the wonderful objects you have up there in the chilly North :)

The range of exposures is based on my HDR capture and processing workflow...

The shortest exposure is chosen based on the brightest star in the frame; that is, the longest exposure such that the pixel value of the centre of the brightest star < 16383 ( the 14bit maximum ).

Then I use a range of exposures ( doubling every time ) so as to smooth out the tones in the HDR image of the bright stars.  Previously, with an HDR image based on sets of exposures every 2 or 3 stops, the brightest stars had an “onion” like appearance with rings of differing exposure values.  Having said that, my processing workflow has changed quite a bit since then ( in particular I now use Pixelmath instead of the build in HDR module in Pixinsight ) and it may be worth checking to see if I can get away with a bigger step size than the 1 stop I am using now.

Cheers

Mike

 

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Fascinating Mike. Thanks for the detailed explanation.  It certainly works well!

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3 hours ago, MikeODay said:

A deeper look ...

FAA8F6C1-BFB1-4F00-826F-E75E09311D62.thumb.jpeg.4cf8d389e88f01a6a3f2ceedc3f6d916.jpeg

NGC 6744 in Pavo ( negative )

I like that tidal stream coming from the main galaxy. Reminds me of Gabany's work. Do you have any plans of enhancing that in the colour image?

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10 hours ago, wimvb said:

I like that tidal stream coming from the main galaxy. Reminds me of Gabany's work. Do you have any plans of enhancing that in the colour image?

I will have to have another look at it - the challenge is the noise; even desaturated it looks pretty bad in the highly stretched colour image.

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On 20/11/2017 at 10:01, Allinthehead said:

Very Nice Mike.

 

On 20/11/2017 at 10:09, toxic said:

thats a very nice image Mike :thumbright:

Thanks Guys, much appreciated.

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