galaxy A peculiar galaxy in the southern sky - Centaurus A ( NGC 5128 )

[MikeODay]

Galaxy Centaurus A ( NGC 5128 ) in the southern constellation Centaurus 

( please click / tap on image to see full size )

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Updated again - to try to bring out more faint detail ...

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Updated images ...

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Originals ...

 

( 100% crop )

Centaurus A is relatively near to us in the local group of galaxies and is around 11 Million light years away. The unusual shape of Centaurus A is believed to be due to an ancient collision between a large elliptical galaxy and a much smaller spiral galaxy. 

With an apparent magnitude of +6.8, Centaurus A is the fifth brightest galaxy in the night sky and in the middle of the 20th century it was identified as being the strongest radio source in the Centaurus constellation.

Details:

Galaxy - Centaurus A ( NGC 5128 )

Image ( Nova.astrometry.net ):
Center (RA, hms): 13h 25m 28.924s
Center (Dec, dms): -43° 01' 25.486"
Size: 60.5 x 41.1 arcmin
Orientation: Up is -89.9 degrees E of N

Telescope: Orion Optics CT12 Newtonian ( mirror 300mm, fl 1200mm, f4 ).
Corrector: ASA 2" Coma Corrector Quattro 1.175x.
Effective Focal Length / Aperture : 1410mm f4.7

Mount: Skywatcher AZ Eq6 GT
Guiding: TSOAG9 Off-Axis-Guider, Starlight Xpress Lodestar X2, PHD2 

Camera: Nikon D5300 (unmodified) (sensor 23.5 x 15.6mm, 6016x4016 3.9um pixels)
Format: 14bit NEF
Long exposure noise reduction: off
Filter: none

Calibration: No darks, just master bias and master flat

HDR combination of eight sets of exposures (27, 28 & 29 April 2017):
85 x 240 sec ISO 800
16 x 120 sec ISO 800
16 x 60 sec ISO 800
16 x 30 sec ISO 800
16 x 15 sec ISO 800
16 x 8 sec ISO 800
16 x 4 sec ISO 800
16 x 2 sec ISO 800

Pixinsight May 2017

 

Links:

500px.com/MikeODay
photo.net/photos/MikeODay
www.flickr.com/photos/mike-oday

[StargeezerTim]

Beautiful images 

[MikeODay]

 

4 minutes ago, StargeezerTim said:

Beautiful images 

 

Thanks Tim - I was a little worried that I may have overdone the saturation; it turned out to be so colourful that I just couldn't help myself  

[mikeyj1]

I see you changed up from the SW 10" to the orion 12" Mike, hows that going?

cheers

Mike

[MikeODay]

Just now, mikeyj1 said:

I see you changed up from the SW 10" to the orion 12" Mike, hows that going?

cheers

Mike

Hi Mike

The combination of Orion Optics CT12 and ASA coma corrector produces much sharper images ( particularly in the corners ).  Also, the longer back focus has allowed me to use an OAG instead of a piggy back guide scope.  This has improved guiding ( eliminated differential flex ) and it also means that the addional weight of the larger 12" scope is somewhate offset by the lighter guiding equipment so I have so far been able to keep using my Skywatcher AZ EQ 6 without any tracking issues.  

It has taken a while though to get consistently round stars.  The problem comes from tilt caused by play in the built-in extension tube ( that is, it is possible to tighten the extension tube locking screw with the extension tube tilted relative to the optical path ).  It just means that I have had to adapt the standard collimation process to come up with a way of eliminating the tilt.  Now Ithat I have gotten used to its quirks I am very happy with the scope and my new setup.

Cheers

Mike

 

[MikeODay]

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[Allinthehead]

Stunning.

[MikeODay]

16 minutes ago, Allinthehead said:

Stunning.

Thanks.

[Rodd]

That's the best Centaurus A I have ever seen.  I thought that F4 Newtonians produced allot of diffraction spikes around stars--you only have 3-4.  Did you do something to eliminate them?   How often do you have to collimate?  

Rodd

[MikeODay]

5 minutes ago, Rodd said:

That's the best Centaurus A I have ever seen.  I thought that F4 Newtonians produced allot of diffraction spikes around stars--you only have 3-4.  Did you do something to eliminate them?   How often do you have to collimate?  

Rodd

Thanks Rodd, that is very kind of you.

They do, and mine does but the brightest stars in this image are only mag +9.  The spikes are a lot longer on brighter stars.  I have not done anything to reduce them here - I quite like spikes

I had quite a bit of difficulty getting the scope initially collimated as the built-in extension tube in the focuser has quite a bit of lateral movement that was introducing tilt.  Since I got that sorted in December I have not had to re-collimate.

Cheers

Mike

[Rodd]

10 minutes ago, mike005 said:

Thanks Rodd, that is very kind of you.

They do, and mine does but the brightest stars in this image are only mag +9.  The spikes are a lot longer on brighter stars.  I have not done anything to reduce them here - I quite like spikes

I had quite a bit of difficulty getting the scope initially collimated as the built-in extension tube in the focuser has quite a bit of lateral movement that was introducing tilt.  Since I got that sorted in December I have not had to re-collimate.

Cheers

Mike

  Did you upgrade the focuser outright of make some other kind of correction?

Rodd

[MikeODay]

Just now, Rodd said:

  Did you upgrade the focuser outright of make some other kind of correction?

Rodd

No I kept the standard focuser.

I introduced another srtep in the collimation routine.

1. retract extension tube fully and lock in place ( note there is now play in the extension tube when it is fully retracted ) and collimate scope.

2. with laser collimater in place,  pull out extension tube to approx. length needed to achieve focus. Tilt extension tube until laser dot is re-centered on primary mirror and lock extension tube in place.

Also, I noticed last time I adjusted focus that fully tightening the focus locking screw also tilts the focus tube slightly causing a further small amount of tilt.  I managed to eliminate the distortion in star shape caused by this by slacking off the screw a little until the stars were round.  I'll need to keep an eye on this.  Oh and tightening the focus locking screw shifts focus slightly

All in all I am very happy with the results I am now getting - it's just a pity that the focuser is not better designed so as to remove all play induced tilt in the extension and draw tubes. If I could find a better focuser that was hole-compatible ( ie re-use same holes without needing to drill ) and could achieve focus with the ASA coma corrector then I would upgrade.

[Shibby]

That is just superb. Very nicely processed, too.

[Rodd]

23 minutes ago, mike005 said:

No I kept the standard focuser.

I introduced another srtep in the collimation routine.

1. retract extension tube fully and lock in place ( note there is now play in the extension tube when it is fully retracted ) and collimate scope.

2. with laser collimater in place,  pull out extension tube to approx. length needed to achieve focus. Tilt extension tube until laser dot is re-centered on primary mirror and lock extension tube in place.

Also, I noticed last time I adjusted focus that fully tightening the focus locking screw also tilts the focus tube slightly causing a further small amount of tilt.  I managed to eliminate the distortion in star shape caused by this by slacking off the screw a little until the stars were round.  I'll need to keep an eye on this.  Oh and tightening the focus locking screw shifts focus slightly

All in all I am very happy with the results I am now getting - it's just a pity that the focuser is not better designed so as to remove all play induced tilt in the extension and draw tubes. If I could find a better focuser that was hole-compatible ( ie re-use same holes without needing to drill ) and could achieve focus with the ASA coma corrector then I would upgrade.

Wow--good to know.  Upgrading focuser is not easy without re-drilling.  I did not know this.  I am really attracted to the f4 Newtonian, but redrilling would not be an option (unless it was done upon purchase by vendor).

Rodd

[alacant]

Great shot and thanks for sharing.

1 hour ago, Rodd said:

redrilling would not be an option

Hi. I think this is a problem with the sw focuser and may also be exacerbated by the OP's 12" tube, but hey, take a look at the photo first;)

laser_jock99's excellent cheap tube modifications for f4 newtonians -ought to be made sticky- outlines simple methods of getting one of these telescopes sky-worthy. I got an ES 208 f3.9 and after following the same guide, haven't looked back since. Don't believe all the nonsense surrounding the impossibility of collimating anything faster than f8! HTH.

[Rodd]

2 hours ago, mike005 said:

No I kept the standard focuser.

I introduced another srtep in the collimation routine.

1. retract extension tube fully and lock in place ( note there is now play in the extension tube when it is fully retracted ) and collimate scope.

2. with laser collimater in place,  pull out extension tube to approx. length needed to achieve focus. Tilt extension tube until laser dot is re-centered on primary mirror and lock extension tube in place.

Also, I noticed last time I adjusted focus that fully tightening the focus locking screw also tilts the focus tube slightly causing a further small amount of tilt.  I managed to eliminate the distortion in star shape caused by this by slacking off the screw a little until the stars were round.  I'll need to keep an eye on this.  Oh and tightening the focus locking screw shifts focus slightly

All in all I am very happy with the results I am now getting - it's just a pity that the focuser is not better designed so as to remove all play induced tilt in the extension and draw tubes. If I could find a better focuser that was hole-compatible ( ie re-use same holes without needing to drill ) and could achieve focus with the ASA coma corrector then I would upgrade.

Do you use autofocus?  Or a B-mask?  Asking because that may change the focuser requirements.

[MikeODay]

8 hours ago, Shibby said:

That is just superb. Very nicely processed, too.

Thanks Lewis, much appreciated.

[MikeODay]

6 hours ago, alacant said:

Great shot and thanks for sharing.

Hi. I think this is a problem with the sw focuser and may also be exacerbated by the OP's 12" tube, but hey, take a look at the photo first;)

laser_jock99's excellent cheap tube modifications for f4 newtonians -ought to be made sticky- outlines simple methods of getting one of these telescopes sky-worthy. I got an ES 208 f3.9 and after following the same guide, haven't looked back since. Don't believe all the nonsense surrounding the impossibility of collimating anything faster than f8! HTH.

The focuser I have is the standard one supplied by Orion Optics.  Now that I have found a way to manage its quirks I am happy with it - it keeps. focus and alignment once achieved.  I just mentioned upgrading as it would save alot of fiddling if for instance I need to recollimate the scope for any reason.

[MikeODay]

5 hours ago, Rodd said:

Do you use autofocus?  Or a B-mask?  Asking because that may change the focuser requirements.

I use a B-Mask.

Cheers

Mike

[Rodd]

Well-with results like that--maybe I should forget autofocus--is that a b-mask withoput computer assistance?

[MikeODay]

2 minutes ago, Rodd said:

Well-with results like that--maybe I should forget autofocus--is that a b-mask withoput computer assistance?

I mount the mask and then, rather than traipsing back and forth between my rolled back shed ( where my laptop is) and the scope, I adjust focus whilst looking at my Ipad screen ( Helicon Remote App ) with my DSLR in Live-view and wifi modes.  As average seeing conditions mean that the central spike moves about a bit, I then confirm focus by taking a 30 sec  Iso 6400 image with the mask in place.  

[Rodd]

5 minutes ago, mike005 said:

I mount the mask and then, rather than traipsing back and forth between my rolled back shed ( where my laptop is) and the scope, I adjust focus whilst looking at my Ipad screen ( Helicon Remote App ) with my DSLR in Live-view and wifi modes.  As average seeing conditions mean that the central spike moves about a bit, I then confirm focus by taking a 30 sec  Iso 6400 image with the mask in place.  

That's basically what i do--Its manual.  there is a software that reads the B-mask image and focuses--kind of like a B-mask autofocus--but i don't use that kind of Mask.  How often do you focus?   

[MikeODay]

18 minutes ago, Rodd said:

That's basically what i do--Its manual.  there is a software that reads the B-mask image and focuses--kind of like a B-mask autofocus--but i don't use that kind of Mask.  How often do you focus?   

As rarely as I can get away with.  I check it every time but I have only had to adjust it may be once every three times I use the scope.  Mind you, that has been around once every few months given the almost nightly clouds that have formed over the Blue Mountains near Sydney for the past 6 months.  As it starts to get dryer now as we head towards winter, hopefully I will get to focus more

 

[MikeODay]

Somewhat less saturated ...

Centaurus A ( NGC 5128 )

[MikeODay]

The star with the double spikes,

is in fact a double, HD 116761 and Herschel 4587 5.2" apart ...