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NGC 6946 - The Fireworks galaxy


ONIKKINEN

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NGC 6946, or the Fireworks galaxy is a spiral galaxy partly obscured by dust in the Milky way giving it a browner than usual look for spiral galaxies. Imaged over 3 consecutive clear nights starting from September 7th, the first night produced excellent data due to exceptionally stable seeing but the second and third not so great. Averages out to decent seeing, but most of the heavy lifting for detail is from the first night. In total i managed to scour 308 x 120s exposures from the 3 nights, to a total of 10h16min of integration.

I processed this with 2 different workflows for colour, the first is a faithful rendition where the galaxy appears as it should, slightly dirty due to dust. For the second i took some artistic license in an attempt to show what the galaxy could look like if it were not obscured by dust.

Taken with a TS ONTC 10'' f/4 newtonian, RisingCam IMX571 OSC camera and a TeleVue Paracorr

Faithful rendition, resampled to around 1''/px:

Fireworks-faithful75p.thumb.jpg.b34f8b897adfaf9d36906a76611cf32a.jpg

De-obscured rendition, also 1''/px:

Fireworks-deobscured75p.thumb.jpg.fb595784326b21f62e87f49d0bc10969.jpg

And an annotated version:

Fireworks_faithful75p_Annotated1.thumb.jpg.76f92520aaf5417282d703dd2877e013.jpg

Not sure how i like my processing with this one yet, we'll see how well it sits with me. I do know that i need to get some Ha at some point, looking at other images of this galaxy reveals that i am missing a huge chunk of it, so that will have to get sorted out whenever possible.

Feedback welcome as always.

-Oskari

Edited by ONIKKINEN
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Really nice, great detail in the spirals, and the fainter outer spirals are coming through too. 

Coincidently I’m aimed up at this one right now, so seeing your result after 10 hours gives me a good benchmark, hopefully mine turns out half as good as yours Oskari.

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11 minutes ago, WolfieGlos said:

Really nice, great detail in the spirals, and the fainter outer spirals are coming through too. 

Coincidently I’m aimed up at this one right now, so seeing your result after 10 hours gives me a good benchmark, hopefully mine turns out half as good as yours Oskari.

Thanks, 2 of the 3 nights were taken from a new spot at an SQM 21.3 location so SNR is very good with the 10 inch. Interested to see yours whenever its ready.


I did integrate 10 hours, but really its not so straight forward. Stacking was weighted where the 2 bad nights have been given a lower weight so they are essentially integrated only "in spirit". Looking at the Siril plot the first night had a higher weight than the 2 subsequent nights combined, so if all the data was good i think the same image could have been taken in somewhere around half to two thirds of the time spent here.

Edited by ONIKKINEN
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5 minutes ago, ONIKKINEN said:

Thanks, 2 of the 3 nights were taken from a new spot at an SQM 21.3 location so SNR is very good with the 10 inch. Interested to see yours whenever its ready.


I did integrate 10 hours, but really its not so straight forward. Stacking was weighted where the 2 bad nights have been given a lower weight so they are essentially integrated only "in spirit". Looking at the Siril plot the first night had a higher weight than the 2 subsequent nights combined, so if all the data was good i think the same image could have been taken in somewhere around half to two thirds of the time spent here.

First night tonight after a day of a lot of rain, so there’s a lot of moisture in the air currently. Guiding circa 1.3” and a HFR in NiNa of ~2.4. So we’ll see, look forward to seeing yours with the Ha details. I’m thinking the upcoming Moon period.

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3 hours ago, CraigT82 said:

Fantastic shots…. The images of bright stars you get from that big newt are just gorgeous. Have you modded the scope on any way or did it perform like that out of the box? 

2 hours ago, 900SL said:

Great colour and detail there Oskari. That new scope looks a winner. All good out of the box? I'm thinking of an ONTC farther down the line..

Thank you! Bear in mind BlurXterminator makes stars appear as good as you want them to, and i gave these ones a fair bit of it since otherwise its easy to lose the galaxy behind them but it is all working very nicely even without it.


Optically the scope seems to be very good, mine has a primary mirror mask reducing the clear aperture to 240mm but also culling any possible mirror edge artifacts (mirror clip shadows for example). Funnily enough i think the mirror mask itself is creating some diffraction effects which can just about barely be seen on the 2 bright blue-ish stars on the right side. The mask looks 3D printed, so the inside edge is not perfectly circular and has some small edges which i think are responsible for the minor diffraction effect. For some peace of mind the scope comes with a report with a ronchi test, intrafocal and extrafocal star tests so chances of being surprised with astigmatism or some other optical nightmare are slim to none.

The slight diffraction thing is better seen in an over-stretched image like so:
2024-09-12T09_39_25.png.959113c7eb1d00aa21593eb0fb1d63fd.png
Of course it is still minor and im not sure anyone would have noticed had i not pointed it out.

Build quality of the all the important parts is very good, the tube is 7mm thick sandwiched carbon fiber with a foam insert and practically indestructible. The mirror cell also appears to be well designed, fully stable in all tube orientations with no slop or pinching and collimation is easy with strong springs creating tension to keep collimation well (i still collimate every time or at least check collimation, just a habit). The spider is a sturdy steel spider and is easy to center with symmetrical vanes, the focuser is whatever you tell them to put on it (not included in price). They figure out the primary to focuser distance based on your choice of focuser or other wishes so there will be no focuser intrusion inside the tube, at least i'd think so since mine couldn't be more perfect.

But in typical newtonian fashion it isn't quite so simple and still needs assembly. It ships in 2 boxes, one contains only the tube, focuser and spider (assembled) and the other contains the mirrors with the primary mounted in its cell in a bomb proof box. The tube shipped in a box about the size of a fridge, i think it could have been dropped off an airplane and survived. Some screws were loose, for example the ones holding the spider to the tube were not even finger tight. Probably shimmied themselves loose in shipping, who knows.

There is also a puzzling decision they have made with the choice of secondary holder and spider, the little dents on the secondary holder and the spider do not match at all and the secondary mirror collimation screws are sitting on the "high spots" between the obvious spots they should be making contact with. Example with measurements below. It does still appear to hold collimation but its not a good design.
Secondarymeasurements.thumb.jpg.f7d4d5f83487c17b687a58f6c14e0355.jpg

So not a perfect scope, i think if someone were to purchase the scope thinking they can just put it on a mount and get going they would be disappointed.

I also asked them to mount the spider in an "x" pattern, so vanes at 45 degrees to the focuser which they said they would do since they build the scope from scratch. They didn't do that though, which was very disappointing for a 3700€ purchase. Overall would still recommend, but not for someone who wants a plug and play scope although i think few people who want a ready to go scope would go for a newt.

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  • 2 weeks later...

Missed this first time around, so thanks for including in your Ha post. IMHO it’s one of the best Fireworks Galaxy images I have seen on SGL, you have taken full advantage of your sky conditions.👍

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2 minutes ago, tomato said:

Missed this first time around, so thanks for including in your Ha post. IMHO it’s one of the best Fireworks Galaxy images I have seen on SGL, you have taken full advantage of your sky conditions.👍

Thanks, the first night is the best data i have ever captured. Essentially perfect seeing and flatlined guiding, the first night only stacked has a fwhm of 1.4'' which is half an arc second better than the second best night i have ever seen. Not holding my breath on getting many of these kinds of nights, but glad i got lucky this time.

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