View Full Version here: : NGC 6744 - spiral galaxy in Pavo
23-05-2012, 08:27 PM
[Added repro version. Thanks for advice from all, especially Greg Bradley!]
Last new moon was the first time with my RC10 under dark skies, so I had a go at a couple of galaxies for a change (up until now I've been imaging at 530mm and mainly targeting nebulae).
Here's my first attempt at processing 7 hours of data for NGC 6744.
Scope: GSO RC10 @ f/8, 2000mm FL
Camera: Starlight Xpress H-18 mono
Filters: Astrodon E series Gen 2
Guiding: SX AO-LF and Lodestar
Image scale: 0.56 arcsec/pixel - a bit small, perhaps :)
Exposures: 24x10m L, 12x5m R, 12x5m G, 12x5m B
I've never imaged a galaxy before at this scale, so I'd really appreciate any helpful comments on things that would improve the image. I'm planning to reprocess it, but still deciding what aspects of the image I'd like to fix.
BTW, the little galaxy at the top left is NGC 6744A.
23-05-2012, 09:09 PM
That's a really nice job you've done, it looks natural , great colour and heaps of detail.
I'd hang that on on the wall !!
23-05-2012, 09:10 PM
Very nice image of this beautiful galaxy!
23-05-2012, 09:14 PM
Nice image Rick, looks like you had a good imaging run. Well Done :thumbsup:
23-05-2012, 09:36 PM
A nice image Rick and a great shot for a first image of a galaxy. NGC6744 is a bit of a toughy and is quite faint.
Its also hard to get a nice colour balance with this one compared to other targets.
So a couple of pointers;
Firstly star sizes seem a little large. Did you use deconvolution on the luminance?
Also see Ken Crawford's tutorial on multiple deconvolution. It can extract more detail which is the name of the game in galaxies.
3rdly the galaxy is bluish with a yellowish core. Your galaxy looks a little grey. Also stars are lacking in colour. So colour can be boosted here.
Selective colour tool is good for boosting individual colours and shades.
Also see free Photoshop plug ins from Neil Fleming for boosing colour saturation and dust in galaxy images.
23-05-2012, 09:42 PM
Nice work, Rick. Glad to see you have your mono camera working properly :) How do you find the GSO RC10?
It looks like you may have plenty of head room to boost the contrast over the background star field (i.e. curves adjustment). I think there may be a slight blue/green colour cast?
23-05-2012, 09:53 PM
Not bad Rick. I agree with Greg about his suggestions and add that doing a minimum filter on the stars will help to enhance the galaxy too.
23-05-2012, 09:56 PM
:) it's beautiful!!
I agree with Greg. Time to start refining those processing skills.
23-05-2012, 10:05 PM
Very kind of you, Mike.
Thanks, Geoff. It was nice to have two days of dark skies,and especially good not to have to set up again on the second night!
Thanks, Greg. I didn't do a deconvolution. My previous attempts haven't been that successful, but I think it's time to get serious and get out the whip and chair :D
I used a PI shortcut for colour calibration and it looks like it didn't work this time. I also tried my usual G2V calibrated extinction factors and that didn't look quite right either. Perhaps I just need to tweak the colours to look like other images of 6744?
Thanks very much for the pointers.
Thanks, Dave. I actually had a different problem with the camera. The cooling was a bit flaky. Fortunately, dithering and stacking got rid of the additional noise. I also found out what was causing the previous dust problem. The shutter coating used on early versions of the H-18 falls off.
I'm quite pleased with the RC10 so far. For the price it's hard to beat. It takes some time to sort out imaging at 2000mm but I think I'm getting the hang of it.
Thanks for your suggestions!
24-05-2012, 12:44 PM
Cool shot. Nice details. :thumbsup:
24-05-2012, 04:29 PM
Excellent result Rick.
24-05-2012, 05:30 PM
Thanks, Paul. I'll give it a go.
I'm working on some new techniques already, thanks Jeanette!
24-05-2012, 07:03 PM
That's one dim galaxy Rick. I had a bash at it last year and had to bin everything x2 to see it with the RC8 so you've done well here.
24-05-2012, 07:48 PM
Nice shootin' Rick.
From Glen Aplin no doubt? Testamony to the dark skies, as I've only ever had any success with this from Wiruna. Even from Peter's it was tough, but there was smoke in the air that night/year as I recall.
I was a bit surprised at stars. Very round, so tracking spot on. Is is possible focus was a smidge off, or cumulative seeing effect perhaps at such small arcsec/pixel?
Regardless, one of the better 6744s you'd find on IIS I'd wager, especially with a big of colour tweaking (again, agree colour quite tough to get right - Marcus did a great one here a year or so ago from memory might be worth peeking at.
24-05-2012, 10:32 PM
The dark skies at Glen Aplin certainly helped, Robin, as Rob suggested. Thanks, mate!
Thank you, Paul.
Rob, the AO does a good job of tracking if you get a decent guide star. I was running it at 3-4Hz most of the night. I was refocusing with FocusMax about every hour as the temperature was dropping quite quickly. The seeing was OK but not fantastic, especially on the Friday night. The other factor is my collimation which I think is not bad, but may not be perfect.
Thanks for your comments. I'm going to miss the next new moon weekend as I'll be on a plane somewhere over the Pacific, so I have a couple of months to spend honing my processing skills on the Glen Aplin data! I also have 7 hours on NGC 4038/4039 that shows some promise...
24-05-2012, 11:09 PM
Really nice. I'm in the same boat, never really given a galaxy a go. No idea where to start, so you're way ahead of me.
Does look like it needs some more blue(?) in the arms, bit more colour as others have mentioned.
24-05-2012, 11:33 PM
I agree, Top Job so far Rick, I tried this faint Gal but gave up on it, Lol, seeing was a bit below par, Great to see what potential it has ? Great show ! !
25-05-2012, 09:18 AM
Thanks, Troy & Bob!
I spent a few hours last night reading up on the PixInsight tools for estimating PSF and deconvolution. By midnight I had managed to run my first deconvolution that didn't make the image look worse, so that's definitely an improvement on previous attempts.
25-05-2012, 09:25 AM
I think they're treating deconvolution as a bit of a deprecated sharpening method in PI. They're recommending the multiscale processing process ATWT and more recently MMT. Maybe try these:
25-05-2012, 10:16 AM
I've been using ATWT and MMT for a while for both noise reduction and sharpening. I don't think they replace deconvolution but they can certainly be used to enhance the image afterwards. Deconvolution attempts to reverse the blurring due to seeing and other effects using an estimated point spread function. This can actually reduce star sizes and recover details. ATWT and MMT just enhance what is already there.
25-05-2012, 10:19 AM
Aah, gotcha. I'm sure I've read they're recommending against it. Will have to go back and read. Again. Man I spend some time on that forum, lol.
25-05-2012, 10:28 AM
Let me know if you find anything interesting, thanks Troy!
I don't know if there's necessarily any right and wrong, but my feeble understanding is that as you never know exactly what the correct PSF is and no so much quality data for deconv to work, ATWT and other contrast enhancing algorithms in PI will often succeed with less ring artifacts etc....
25-05-2012, 06:56 PM
Have you looked at DynamicPSF, Rob? It appears to provide a reasonable method for estimating the PSF by measuring a sample of suitable stars from a linear image. It also appears that best practice of using a deringing mask, global deringing and masking low SNR areas them can control artifacts pretty well.
I'm convinced that, in theory at least, deconvolution can provide benefits that the other tools can't. Unfortunately, it's a fairly daunting process in PI. I'm sure it gets easier with practice. And that's what I'll be doing again tonight ;)
25-05-2012, 07:24 PM
Nice work Rick, it's a faint galaxy that is not easy to capture. The next test is in the processing of the data [and that's what I have found].
Great work, enjoy the processing challange.
25-05-2012, 07:35 PM
Thanks, Steve. It has been educational so far!
Only rarely Rick, but the tutorial using lunar images blew my mind away with what someone with decent knowledge of how to use it could improve an image must confess.
25-05-2012, 09:05 PM
I'm definitely getting tighter stars and more detail in the galaxy itself from the deconv. The hard part is knowing how far to push it. I often look back at my efforts afterwards and think, "hmmm... I sharpened/denoised/saturated/whatevered that just a bit too much" :rolleyes:
26-05-2012, 09:03 AM
Yes that is the trick.
I usually use 40 iterations or less in CCDstack positive constraint.
Basically Ken's technique is to do several versions at higher and low levels and then combine them in Photoshop as you see fit.
I believe how much decon you can use also depends on the image. A dim image will not take much but one that is stong will take more.
I judge by the star shapes. But if you want detail in the galaxy you could just judge the galaxy only, not worry about deformed stars and then blend in the galaxy sharpening only in a masked layer in Photoshop.
How you do all this in PI I don't know.
26-05-2012, 11:59 AM
Thanks for the suggestion, Greg. You can blend using PixelMath in PI but it's not quite as interactive. I'll have play with that as well...
26-05-2012, 02:11 PM
I'm still working on this image trying lots of different techniques and options, but here's the current version. It's certainly a lot better than my original attempt, at least IMHO :D
26-05-2012, 04:11 PM
Definitely like the new version Rick!
26-05-2012, 06:30 PM
Getting there Rick.
The galaxy is too magenta. Try Photoshop selective colour and tone back the magentas and add some yellow to the blues and you should get that nice galaxy sutley bluish arms.
Starting to look very nice! Plenty of great data to get that far for sure.
27-05-2012, 04:15 PM
Ta, Greg. Had a go at that. It's definitely an improvement. Thanks for the lessons!
Thanks, Rob. My data collecting ability has always exceeded my ability to process. Maybe it'll catch up one day! It takes a while to develop a good sense of aesthetics for these images, too. There are lots of subtleties that you don't notice at first.
27-05-2012, 04:16 PM
27-05-2012, 04:49 PM
That is a very nice repro Rick. It's a great image.:thumbsup:
27-05-2012, 10:24 PM
Thank you, Lucas.
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