m83 - The Southern Pinwheel

[Dave882]

My first proper galaxy project for the season, making use of 2 clear nights (the first for several weeks for me). Moving right overhead for us southerners and only 15 million light years away, m83 is such a joy to image - and even from my B7 location almost no gradients an hour on either side of the meridian.

I thought I'd try a slightly different approach and shoot 30sec exposures to try and minimise star bloat/oversaturation. About 11hours, and well over 1200 subs, I decided to stack them in APP in roughly 1-2hr batches otherwise this was going to take ages. The advantage of this was I was able to cherry pick the best data (APP reported FWHM of the sub-stacks ranging 1.9-3.1) and ended up keeping the best 5.5hrs. I did some comparisons trying to include the inferior data in the stack and the result was noticeably noisier and lacked detail, so as much as it hurts chucking 6hrs of hard work out it needed to happen. oh to be able to shoot in a location with consistent good seeing sigh

Anyways- here's the rundown:

681 x 30sec subs (no moon)
gain 100
C14 non edge @f7 with the Starizona reducer LF
EQ8 pro
Asi2600mc pro (no filter)
Asi290mm / celestron OAG
ASIAIR pro / APP / GIMP / LR
Binned (scaled) 80% in processing

Here's the bigger version. (https://1drv.ms/i/s!ArpSiLT3VkGHiPNLNzzP3ze9IshLcw?e= LJjhEq)

Comment/critique or suggestions welcome.
Thanks for dropping by! Clear skies all!!

[alpal]

Hi David,
nice data at long focal length.
I had a play around with your image in Photoshop and Fitswork4.
I believe I was able to make it better but of course I wouldn't
post my efforts without your permission and
the word "better" is subjective.
I made the stars smaller and used blurred layer masks on selected areas
to give more contrast and sharpening to the center of the galaxy
and another mask to increase brightness in the outer areas.
I also added a tiny bit extra colour saturation.


So I think I could do even better on the original stack so I will leave it to you
to maybe have another go at the processing if you want to?


cheers
Allan

[Startrek]

Dave,
A great capture of M83 to start your Galaxy season
30 sec subs too
Colour and detail is excellent
A1 for effort alone
Don’t you love Sydney’s LP 😤
I captured the same target a few nights ago under a 50% moon with 60 sec subs ( noise fest ) see what I can throw together with my little 6” Newt

Cheers
Martin

[ChrisD]

You've definitely got some good data there.

I have a C8 at ~F7 which I use for galaxies, and don't have any experience with a C14, but I'm surprised at the star bloat you're getting for a 30 second sub. Have you checked collimation on the C14? How are you achieving focus? Do you use a bahtinov mask or Asiair autofocus with an EAF?

I also agree with alpal, I think there is more detail to be teased out in processing.

Overall though, good work.

Chris

[Dave882]

Hi Allan yeah I’d love to see your efforts mate more than welcome to add them. Yeah my post processing is very basic with some minor adjustments such as colour calibration and LP gradient removal in APP and noise reduction but no star masks, decon or star reduction so definitely agree this is an area to work on. Quite certain I’ll enjoy your work! :)

[Dave882]

Cheers mate yes I got a bit of a taste for B4 imaging with a few visits out of town last month but unless it’s clear and moonless it’s not worth the effort. The council has just put in huge light towers across the road from me so it’s gone from bad to worse here but at least m83 (when at the meridian) is pretty much straight overhead so very little gradients surprisingly until I added the extra data. Looking forward to your efforts !

[Dave882]

Thanks Chris and really appreciate your input. I did check the collimation as best as I could (seeing limited of course) and looks pretty good. Nailing focus with the c14 is seriously like shooting at a moving target. When the temp is dropping I do a refocus on nearby star with bahtinov mask every 1hr and even then it’s moved quite a bit. I have a zwo eaf in the back of the cupboard somewhere but still haven’t had time to work out how to get it all connected. Just bing lazy I guess lol.

As I mentioned to Allan my post processing is really basic. No star reduction or masks so unfortunately that’s going to work against me. This was my first time since about Sept22 having my f7 image train going so also got some tilt issues to deal with too (hence the crop image). Anyways I think I’ll have another shot at a repro soon and perhaps even bite the bullet and get PI to get the most from the data.

[alpal]

David,





OK Thanks David,
to post at a reasonable size considering the 200k file size restriction I choose 1000 pixels wide.
The first one is your original,
the 2nd is after some processing by me.
Is that better?


cheers
Allan

[ChrisD]

I'm definitely not the most experienced astrophotographer, so there is a better than average chance that you already know or use the things I'm about to suggest, but here goes. :)

I think that that focus and collimation on a cat are critical to getting the detail into an image. It's easy to get 90% of best focus and collimation, but that last 10% is where maybe 50% of the fine detail lives.

I use a tri-bahtinov mask and touch up the collimation maybe twice or more a night, pre and post meridian due to minor mirror flop. The tri-b mask makes it so much easer to hit optimum collimation.

You're already using an ASIAIR pro and with the EAF attached you can set the autofocus to trigger on temperature changes or every hour while in Autorun. I would also use Star Detect (i think thats what it was called, I no longer use Asiair) which will display the average HFR in an image. During autorun I would run Star Detect on images and if HFR had increased by maybe 10% I would manually trigger an autofocus.

If you're still using the original focus control, make sure the focus, either auto or by hand, finish with the mirror moving in, otherwise the mirror will slowly relax back under gravity over time. There is a reverse selection for the EAF, again from memory it has to be selected to "reverse" so that focus finished going in.

Chris

[AstroViking]

alpal - of those two images in your most recent post, I think the 2nd one with the extra processing has more depth to the colours and shadows. The colours certainly seem to leap out a lot more than in image 1.

Very nicely done!

[Dave882]

Allan- that’s great! I really appreciate taking the time to work with that. Yeah defiantly pulled more detail out and with your skill haven’t introduced more noise. Normally, that’s the limiting factor for me for how much I can push the data but you’ve gone up a level. I have to say I kinda like a bit more neutral colour in the dust lanes (bit less red) and if I repro will probably lean in that direction. The Ha regions gotta have some nb to finish it off but need a bit more gear to make that happen :P.

Chris- I think you’ve successfully convinced me to suck it up and get the eaf working even if there’s a bit of trial and error I know it’ll benefit things. Regarding collimation I’m pretty confident in that being quite close- I usually use the star defocussed rings and then the airy disk pattern as best as the seeing will allow. I’ve tried a tri bahtinov mask but cold never work out the correct adjustments… have you got a link for a good procedure for using one? But as you say you can get movement in the collimation over the meridian which needs adjustment…except its often on auto run and I’m in bed at 3am lol

[alpal]

Thanks Steve.
It didn't take long - just a few adjustments.

[alpal]

David,



Thanks David,
it is a little bit red but I stuck to your colours and only
added a tiny bit more saturation.
It can be 1,000 different shades especially if you use LAB mode.
If you show the full size 3494 x 3057 pixels it will show noise.
You need to pick a final size which is suitable for your data -
that is probably between 1000 pixels wide and 1,500 pixels wide.


Louie deals with masks in some of his videos here:
https://www.youtube.com/@astroprocessing665


cheers
Allan

[pkinchington]

Hi Dave,
Nice one - I like the galaxies in the background as well. :thumbsup:
Cheers Kanga

[Addos]

outstanding target for that big beast of a scope Dave. Great job with the background, once again!

[atalas]

Very nice shot Dave and nice improvements by Al :thumbsup:

I shot this with a RC12 a few years back from Padstow and It isn't easy.....had a hell of a time trying to get a nice flat background like you've got here.

[Dave882]

Thanks guys much appreciated! I think a repro is in order just struggling to find the time recently to sit on the computer.
Allan- regarding your re-sizing suggestion can I ask how you approach this and if there’s any particular program /algorithm you use? Cheers

[alpal]

David,



Just objective based on my opinion.
There has to be some limit to the ideal size -

past a certain size there is nothing more to be gained.



cheers
Allan

[Paul Haese]

This is a pretty good image for two nights imaging Dave. Perhaps look at only keeping data below 2.8"FWHM. It might not seem much of a difference but you will have sharper data to process and therefore less blurring to deal with.

The colour needs to be less magenta, the galaxy looks to be magenta rather than little pockets of magenta. One has to be careful about the impact of the those regions bleeding into the blue stars in the spiral arms. I know for a fact that it is one of David Malin's pet hates.

Overall though a good image in my opinion.

[strongmanmike]

Loving this city sky/Moon, galaxy imaging, go the C14 :thumbsup: Agree with Paul, just a tad magenta :)

Mike