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Southern Pinwheel Galaxy at 750mm

dslr dso imaging Celestron SCT astrophotography
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#1 BQ Octantis

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Posted 24 January 2019 - 04:31 AM

I tried my hand again at processing my shot of the Southern Pinwheel Galaxy through my C5/750 from back in May. The results were far superior to my previous results in July—here's the full-scale crop:

 

Southern Pinwheel Galaxy
Southern Pinwheel Galaxy, 2018-05-13, 78˚ elevation
Celestron C5/750 f/6 SCT, Canon T3i (unmodified)
1×180 sec@ISO 800, no darks or flats
Skywatcher SkyView Pro EQ Mount (unguided)
Aligned & stacked in Lynkeos 2.10
Processed in Photoshop CS5 w/Annie's Astro Actions v7.0
Full sensor scale, cropped to 1600×1067
Tropic of Capricorn, NT, Australia
 

Though noisy, the results are making me reconsider getting an f/4 Newt. Per the numbers, I think I'll retry with 30 second subs at ISO 6400 and integrate for an hour or so…

 

BQ


Edited by BQ Octantis, 24 January 2019 - 04:32 AM.

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#2 pyrasanth

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Posted 24 January 2019 - 05:13 AM

There is a lot of noise in the image and I believe some of it would be removed using darks if you could maintain there about the same temperature through out the imaging session. I would stack around 15-20 darks and apply to your subs.

 

If you can use Pixinsight there are some excellent noise correction tools like cosmetic correction which would remove most of the hot & cold pixels.

 

The difficulties which DSLR users face is temperature regulation which makes hot & cold pixel correction harder as these vary according to temperature so your not shooting within a constant set of parameters. 

 

The image has potential so a good improvement so far.



#3 Araguaia

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Posted 24 January 2019 - 07:22 AM

I know nothing about AP, so I will limit my comments to framing.  I liked the 200mm image better.  You don't really get more detail in the galaxy itself in the 750mm, so I think the larger field of the other one, with those two wonderful bright stars and well arranged smaller asterisms, both has more information and is more aesthetically pleasing.

 

Then again, my favorite wildlife photos are not close-ups, but ones that show context and habitat as well.



#4 BQ Octantis

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Posted 24 January 2019 - 07:51 AM

There is a lot of noise in the image and I believe some of it would be removed using darks if you could maintain there about the same temperature through out the imaging session. I would stack around 15-20 darks and apply to your subs.

 

If you can use Pixinsight there are some excellent noise correction tools like cosmetic correction which would remove most of the hot & cold pixels.

 

The difficulties which DSLR users face is temperature regulation which makes hot & cold pixel correction harder as these vary according to temperature so your not shooting within a constant set of parameters. 

 

The image has potential so a good improvement so far.

Thanks, mate! Agreed on the darks, but it's quite a challenge to make 180-sec darks without an intervalometer…at some point, I may get one. For the time being, though, I think I just need way more lights…

 

BQ



#5 BQ Octantis

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Posted 24 January 2019 - 07:56 AM

I know nothing about AP, so I will limit my comments to framing.  I liked the 200mm image better.  You don't really get more detail in the galaxy itself in the 750mm, so I think the larger field of the other one, with those two wonderful bright stars and well arranged smaller asterisms, both has more information and is more aesthetically pleasing.

 

Then again, my favorite wildlife photos are not close-ups, but ones that show context and habitat as well.

 

Thanks for the feedback, mate. I also prefer the wider fields—and the 200mm has become my favorite lens for most targets for that reason. The 200 does pretty well from corner to corner, but the C5/750 is pretty much limited to the center 10-20% of the field—the rest has too much coma to be usable (other than for effect, I suppose).

 

Cheers,

BQ



#6 Araguaia

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Posted 24 January 2019 - 08:56 AM

I think the unconscious reference for close-cropped images ends up being Hubble.  Wide field images capture something that the big telescopes can't, and in my opinion capture some of the magic of looking through the EP.  Part of it is the stars, that usually look so much better in wide field AP. 



#7 BQ Octantis

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Posted 26 January 2019 - 08:48 AM

Turns out, there's great synergy between the 200 and the 750. I pasted and aligned the 200mm output on the 750 image. As expected, shot noise went way down, but I lost a bit of resolution. But scaled to 50%, the output looked better than each contributor:

 

IMG_4206_f2.8assist.jpg

 

BQ


Edited by BQ Octantis, 26 January 2019 - 08:49 AM.

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