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 Post subject: Astrophotography...
PostPosted: Fri, 09-02-18, 10:46 GMT 
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This thread continues some discussions started here:

http://forum.celestialmatters.org/viewtopic.php?f=4&t=926

Below there are two never elaborated DSOs shots made at our astronomical club with a monochromatic SBIG STL6303 CCD camera on a 14" f/8 OfficinaStellare Ritchey-Chrétien scope riding a 10Micron GM2000 QCI mount bolted on a fixed pier. Aside the scope's aperture and the expensiveness of the equipment in general, is interesting to show - for the sake of discussion - what a good mount can do.

Attachment:
M1_201502122043600sec1x1_L3.jpg
M1_201502122043600sec1x1_L3.jpg [ 129.86 KiB | Viewed 536 times ]

This is a single 10min. pose of M1 in luminance only binning 1x1. The scope here was guided by a Starlight Xpress SXVF H9 CCD camera on a Vixen NA130S 5" f/6 refractor. The weather conditions were optimal with average seeing. In these conditions the tracking would have continued for hours, but as you can note some stars are already saturated as it is.

Attachment:
Ngc253_201711102333180sec2x2_L1234_median_1024px.jpg
Ngc253_201711102333180sec2x2_L1234_median_1024px.jpg [ 112.32 KiB | Viewed 536 times ]

This is a stacking of seven luminance poses of 3min. each one binning 2x2 of the low altitude NGC 253 (Sculptor Galaxy) imaged in prohibitive windy conditions, with discontinue breeze blowing up to 60km/h. In this case the scope was not autoguided because the guiding scope was idle by the spectrometer. Without the wind the mount alone would have chased for tens of minutes.

Bottom line:
As you know, in AP the mount is all. I do not advise such a expensive kind of mounts of course, since with lesser ones you can get good results too.

P.S.
I don't do AP, I'm a visual only guy and I deal with the club's optical scopes, but often I do coadiuvate what the imagers does.

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 Post subject: Re: Astrophotography...
PostPosted: Fri, 09-02-18, 15:37 GMT 
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Great shots!
Of course, being able to expose several minutes greatly improves the quality and simplifies the processing a lot!.

Here's an example of an object of similar size and brightness as M1 above, seen through my limited equipment. This is a crop, of course, and the weak red-sensitivity of the unmodified D7200 is obvious.


Attachments:
File comment: M27 - Dumbbell Nebula
100 exposures of 30 seconds each

Hantelnebel-2017-08_(100x30s_siril).jpg
Hantelnebel-2017-08_(100x30s_siril).jpg [ 693.28 KiB | Viewed 527 times ]
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 Post subject: Re: Astrophotography...
PostPosted: Fri, 09-02-18, 20:01 GMT 
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Indeed for those objects a modified DSLR camera is mandatory. None the less it is a cool shot anyhow! You could try to shot it with a narrow band interference filter (Ultra High Contrast: lines Ha, Hb, OIII only) in front of the camera (threaded on the nose piece) just to add some poses where is blocked the unnecessary light. You should gain some red because the lowering of the whole spectrum thermal noise. If the filter doesn't work for you with the camera, I can assure it will work in visual mode: just M27 maybe is the best nebula in which the filter's enhancement is very apparent.

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 Post subject: Re: Astrophotography...
PostPosted: Sat, 10-02-18, 14:56 GMT 
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Good that your took the initiative, fenerit.

I was totally engaged with organizing and celebrating 2 almost coincident important birthdays during the past days ;-). Also I was still waiting for reactions by CC (Chuft) which didn't arrive, however.

Perhaps it is of some interest to compare the above BW galaxy shots with the corresponding rendering by celestia.Sci:

Attachment:
Ngc253_201711102333180sec2x2_L1234_median_1024px.jpg
Ngc253_201711102333180sec2x2_L1234_median_1024px.jpg [ 112.32 KiB | Viewed 501 times ]

[click on image by all means ]
Attachment:
ngc253.png
ngc253.png [ 336.2 KiB | Viewed 498 times ]


Some more will come soon...

Note in celestia.Sci, a toolbutton turns "celestia"-blue, if a function of it is active. Here, it's the equatorial grid and the bright star labelling...

Cheers,
Fridger

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 Post subject: Re: Astrophotography...
PostPosted: Sat, 10-02-18, 15:46 GMT 
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Absolutely beautiful!
I wish I could see this on my screen...

How does the celestia.Sci rendering of the Leo Triplet look like?

I really hope to get a better picture of that one soon. If only the weather would get better!

@fenerit: I also thought about using filters, especially as I'm fighting with a lot of light pollution as well. But at the moment, I'm mostly limited by the short possible exposure times, and with filters I would have to expose even longer.


Attachments:
Leo-Triplet_dt_01.jpg
Leo-Triplet_dt_01.jpg [ 709.5 KiB | Viewed 495 times ]
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 Post subject: Re: Astrophotography...
PostPosted: Sat, 10-02-18, 15:57 GMT 
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schreiberste,

here is the celestia.Sci rendering of the Leo_triplet around M 66:

[click on image by all means]
Attachment:
Leo_triplet_M66.png
Leo_triplet_M66.png [ 189.79 KiB | Viewed 494 times ]


Of course the celestia.Sci rendering can also display in much higher resolution...

Fridger

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 Post subject: Re: Astrophotography...
PostPosted: Sat, 10-02-18, 22:29 GMT 
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Nice field, schreiberste. Leo Triplet is a favorite sight of mine.
Fridger: you did a great work with the galaxy renderer, hope we will see it as soon as possible. Just to find the "hair within the egg", Leo Triplet's component NGC 3628 galaxy, albeit dim, has what is the most easy visual recognizable dust lane of the whole galaxies zoo along with M104, NGC 4565 (Needle Galaxy) e few others. There is way to add it?

Attachment:
NGC3628.png
NGC3628.png [ 361.28 KiB | Viewed 483 times ]

20x120sec luminance binning 2x2

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 Post subject: Re: Astrophotography...
PostPosted: Sun, 11-02-18, 11:05 GMT 
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Wow, great details in this NGC 3628 shot.
Is this a crop or down scaled?
Now I wish even more that the weather would be better and I could try to get a better image of the triplet.

Regarding the dust lanes - what blending mode is used in celestia.Sci for rendering the particles? Is it all additive? Maybe one could add some dark particles in alpha blending mode around the outer disc border, which would work as dust lanes when the galaxy is seen edge-on? Are the particles depth-sorted, or are they just rendered randomly on top of each other - which would work for additive blending, but not for alpha blending?

On the other hand - please don't start a galaxy rendering project right now. I'd rather see a release soon. :D

Steffen


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 Post subject: Re: Astrophotography...
PostPosted: Sun, 11-02-18, 11:12 GMT 
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fenerit wrote:
Just to find the "hair within the egg", Leo Triplet's component NGC 3628 galaxy, albeit dim, has what is the most easy visual recognizable dust lane...

Well observed, fenerit! You pointed out one of the remaining few rendering limitations in celestia.Sci.

Let me do a quick summary for DSOs:

The DSO rendering algorithm in .Sci rests on symmetry, the Hubble classification (for galaxies), 100% computer-based automatic rendering (GLSL shaders) and the use of the known global data (per DSO) from the leading scientific catalogs, such as position, spacial orientation AND the B-V color index.

  • The globular clusters are best off since they show almost perfect circular symmetry and many statistical data are available, such as Hertzsprung-Russell distributions within globulars and surface brightness distributions. The colors of globulars and their spacial shapes are close to perfect for ALL globulars associated with the Milkyway.
  • Limitations: Open clusters and most gaseous nebulae (lack of symmetry)
  • Elliptical and lenticular galaxies turn out almost photorealistic and form a large fraction of known galaxies in the local group volume (~50%). Again there are symmetries(e.g. ellipsoidal, ....)
  • Spiral galaxies occur with ~44% and Irregular ones with ~6% in the local group volume. An important and successful assumption is that Spirals have an approximately circular shape at zero viewing inclination. Together with the B-V index a surprisingly good overall rendering of 10937 galaxies resulted (including the full revised NGC/IC catalog).
  • Limitations: 1) Individual features, like asymmetrically placed dark lanes (see your example, or e.g. the Sombrero galaxy (M104)). 2) Certain gravity-based shape distortions in case of (almost) colliding galaxies. 3) Ambiguity of counter-clockwise versus clockwise rotation sense of spiral arms. In .Sci all spiral arms are assumed counter-clockwise. Clockwise rotation sense then means that the spiral shows it's backside to the viewer. Unfortunately, there seems to be only an empirical strategy for deciding available: looking at best photographs of the objects in question!


I hope this compact summary is somewhat useful in further comparisons with Astrophotography. No intention to snatch this interesting thread for celestia.Sci, Steffen ;-)

Cheers,
Fridger

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 Post subject: Re: Astrophotography...
PostPosted: Sun, 11-02-18, 13:40 GMT 
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t00fri wrote:
I hope this compact summary is somewhat useful in further comparisons with Astrophotography. No intention to snatch this interesting thread for celestia.Sci, Steffen ;-)
Cheers,
Fridger

Oh no, I find very interesting to show these comparisons. Maybe the dust lanes for these few galaxies could be made by point sprites in Cham's fashion.
schreiberste wrote:
@fenerit: I also thought about using filters, especially as I'm fighting with a lot of light pollution as well. But at the moment, I'm mostly limited by the short possible exposure times, and with filters I would have to expose even longer.

I know; just I want you get a better mount! Aside the jokes, FYI, with filters the result is a tad different. Because our camera is monochromatic and the filter carousel can hold up to 5 filters, we are forced to do some choices, knowing also that is a PITA to deal with RGB filters since the filter wheel is inside the camera's chassis and the camera may be tear down and unscrewed. Hence either LRGB filters or the nebular ones: no enough room for both. Thus we leave the nebular ones in it. This fact and the long-standing habits of imaging in black and white harking back to the good old days of the film cameras - where the exposures often were shuttered off quickly because the poor autoguiding man did fall asleep - does yeld the monochromatic shot's supporters alive.
Below M27 in a stacks of luminance, Ha, OIII, SII 4x180sec each one binning 2x2 and processed via RGB channels. You can note that the image is not a true LRGB image because the stars are lacking of the full spectrum colors; just a "purpish" color in those in which is mixed a strong Ha emission with a Oxygen line. After the elaboration, where your DSLR camera shows the intense green, here is shown also the yellow.
Attachment:
M27.png
M27.png [ 697.23 KiB | Viewed 461 times ]

schreiberste wrote:
Wow, great details in this NGC 3628 shot.
Is this a crop or down scaled?
Steffen

Unfortunately, all the images quickly availables to show here are images from the original CCD pixel array of 3060x2040px either scaled down or cropped for web display and "social" purposes. I'm authorized by the other club members to post these shots on Celestial Matters forum. We have an archive of hundreds of FITS neither elaborated nor converted waiting for a public domain display.
The CCD camera has 6 Mpx and each pixel is 9x9 microns. The field resolution after the scope optical chain is 32.8' x 21.8', so the Leo Triplet altogether cannot fit in it. NGC 3628 is the bigger member of the three and it was imaged apart. If some images are scaled up I will warn about this. If can be useful to evaluate the relevant size of the objects in this images' messy misuse, below there is a shot of the Stephan Quintet in Pegasus:
Attachment:
Quintetto_di_Stephan_elab-part.jpg
Quintetto_di_Stephan_elab-part.jpg [ 235.29 KiB | Viewed 461 times ]

Single exposure 300sec binning 2x2

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 Post subject: Re: Astrophotography...
PostPosted: Sun, 11-02-18, 14:15 GMT 
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Fenerit,
fenerit wrote:
Maybe the dust lanes for these few galaxies could be made by point sprites in Cham's fashion.

It is not a question of modeling these dust lanes. With sprites & GLSL shaders this is not difficult. I do have dust lanes in all edge-on galaxy views. But the lanes always appear symmetrically.
Here is the generic morphology of edge-on galaxies that reproduces pretty well in celestia.Sci:

Example NGC 891
-------------------
[click on image for more details]
Attachment:
HWu12.jpg
HWu12.jpg [ 226.8 KiB | Viewed 459 times ]


Don't forget the .Sci code is meant to manage the rendering without human interference (no "handicrafting") for many thousands of galaxies...

Cheers,
Fridger

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 Post subject: Re: Astrophotography...
PostPosted: Sun, 11-02-18, 14:52 GMT 
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Referring to fenerit's above photo of Stephan's Quintet (NGC 7320).

The best photo is the one below from NASA. Note however it is a composite containing various non-standard wavelengths (IR, UV): The various ranges are identified through these camera designations :
Attachment:
Screenshot_20180211_164834.jpg
Screenshot_20180211_164834.jpg [ 34.12 KiB | Viewed 451 times ]


[click on image by all means]
Attachment:
StephansQuintet_NASA.jpg
StephansQuintet_NASA.jpg [ 36.8 KiB | Viewed 457 times ]

The blue galaxy (top left) is actually a foreground galaxy, while the three others are muuuuuuuuuuuch farther away and show already signatures of mutual gravitational interactions due to ther spacial closeness.

Here is the comparison from celestia.Sci (using the SDSS color profile!):
The computer got the SDSS colors and morphologies quite right, I'd say.

[click on image by all means]
Attachment:
Screenshot_20180211_154322.jpg
Screenshot_20180211_154322.jpg [ 70.97 KiB | Viewed 457 times ]


Fridger

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 Post subject: Re: Astrophotography...
PostPosted: Sun, 11-02-18, 17:56 GMT 
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t00fri wrote:
Don't forget the .Sci code is meant to manage the rendering without human interference (no "handicrafting") for many thousands of galaxies...


Yes, of course. My thoughts were addressed to add-ons creators. Now another 3D rendering challenge: NGC 4038 and NGC 4039 (The Antennae) galaxies:
Attachment:
201405232342600sec1x1_L1_rid_elab.jpg
201405232342600sec1x1_L1_rid_elab.jpg [ 480.9 KiB | Viewed 445 times ]

single luminance exposure 600sec binning 1x1

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 Post subject: Re: Astrophotography...
PostPosted: Sun, 11-02-18, 18:57 GMT 
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Oh yes, the Antenna galaxy, NGC 4038/9!

In celestia.Sci the Antenna galaxy is automatically built in terms of two irregular colliding galaxies, each with a pink HII star creation region on its bluish "back". The bluish base color is chosen by the computer due to the low B-V color index = 0.43. Here is a direct comparison with your BW photo.
[click on image by all means]
Attachment:
NGC4038-39.jpg
NGC4038-39.jpg [ 137.63 KiB | Viewed 441 times ]

Of course, the two faint "antennae" and any other gravity effects are missing in the .Sci rendering.

Finally, here is a superhigh resolution photo as well (NASA, ESA and the Hubble Heritage Team)
[click on image by all means]
Attachment:
AntennaGal.jpg
AntennaGal.jpg [ 53.25 KiB | Viewed 441 times ]


Cheers
Fridger

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 Post subject: Re: Astrophotography...
PostPosted: Sun, 11-02-18, 20:05 GMT 
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Nice! Now, let suppose one wish to render the tidal disruption/interacting bridges between galaxies: what should be the procedure? Do one need to parallelize a new class of shader objects shaped like arcs, rings, "C", "S", "J", "integral sign" profiles and then call for them by the single peculiar galaxies (e.a like those in the Arp catalogue)?

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