RCC - M51, 4 hours from Bortle 5, is there more possible?

Daniel Arenas:
Hi Mina,

So in that picture, you haven't used any kind of filter at all? I say that to try to reach some kind of explanations about halos.

Clear skies!

I used my usual UV/IR Cut filter in a filter drawer, it's not even a good one, cheap TS version, 2", because apparently, the 183MC Pro doesn't have an UV/IR Cut filter.

Clear Skies to you

andrea tasselli:
Mina,

You only have a 80mm ED doublet so no surprise with either the issues with bright stars' haloes and the general poor dynamic of the image (and no Ha, this is hard to come by without Ha filter and even with that it isn't that simple). Put simply: you cannot afford the image scale you're imaging at. And 4 hours of RGB data is simply not enough, at all. Think 3 times that and you'll be in the right ballpark.

On the processing side you are overdoing it in more ways than one. Rather than go and deconstruct the process I'd rather have a go at it, if you're willing to share the stacked image and I shall share the processing with you.

Hi, thanks for your answer.
What do you mean exactly with I can't afford the scale I'm imaging at? My guiding is half my image scale, my stars are round... Might be seeing limited, I don't know... or light pollution... or too small of an aparture, but the one thing I'm vouching for is that my guiding is 100% good enough for a 1.1" image scale.
Yeah, I think 4 hours is too little as well, sadly clouds came and I had to stop imaging, and ever since it was rainy / cloudy sadly.

Here's the raw stack: https://drive.google.com/file/d/1B99LQ8RYAy62_3vlIYsWHocAGHQqMoe2/view?usp=sharing

Curious what are you gonna do with it, also I hope you can explain a bit what you did with the data, so I can learn!

edit: regarding the Apo - it's the one with FPL-53 glass, at least, I apparently selected the wrong one in Astrobin. plus I want to sell it, I want a bigger scope - probably going full reflector, no more CA and bloated stars hopefully, a small 6" on the CEM25P, and a 8" on a second, stronger mount which I'll buy in the Q3 this year likely. I'm sadly kinda obsessed with galaxy imaging, I need more aparture for that, that's obvious...

So basically my aparture is too small to resolve that scale properly, add in with light pollution on too of that - do I understand this correctly?
A scale around 1“ would be better done with a bigger scope then, more light gathering abilities - I assume then the smaller pixels become less of a problem, especially with a fast scope? Even if the image scale would be the same / slightly smaller, because bigger aparture > more resolving power?

Well, I just run a regular 0.8x reducer - in hopes of faster light gathering and increased image scale - it‘d be even smaller with the 183mc pro… I see lots of people reducing their 80mm doublets like eg a WO ZS to a faster focal ratio..

I dunno.  Did you have any thin cirrus passing through during imaging?  That might cause some haloes.

I think something might have gone awry in the processing.  I shoot from a Bortle 6 so if anything, my skies are worse.  But for reference, I got this after 3 hours on a somewhat moonlit night:

https://www.astrobin.com/a3tu2v/

Similar speed (f/5.4 vs. your f/5.6) and somewhat similar focal length (540mm vs. your 450mm)

So something tells me it's the processing, not the data...which isn't the worst thing.  Precisely the opposite, because if the underlying data is good, it's very fixable.

The data looks a bit "flat", with some loss of contrast particularly around the spiral arms.  On the plus side, the cores aren't blown out and the dust detail near the center of both NGC 5195 and M51 look nice.

If it helps, here's my general workflow for a OSC camera:

Stack in Deep Sky Stacker (yes, DSS.  I'm THAT "old-school"...)
Dynamic Crop
DBE
BlurXTerminator, default settings
Photometric Color Calibration (can't get SPCC to work for some reason)
NoiseXTerminator, 0.70 overall / 0.15 on details
Histogram transformation (can't get GHS to work, either) until the histogram peak is ~0.20
NoiseXTerminator, ~0.50 / 0.15 (less aggressive round, if needed at all)

Then the "fun begins":

Rename image to "glow"  (or whatever suits you)
Starnet++ V2, rename stars-only image "stars" (or something else)
Adjust color saturation on "stars" image, set it aside.

"Glow" image:
Extract Luminance channel
Using Histogram transformation, slightly stretch it and then clip (yes, clip) the left side until ~45% to 50% of all pixels are clipped.  Use preview if necessary.
Select the newly-created luminance mask but *invert* it and find the general background illumination (mine's often ~0.20 to 0.24).
Using Curvestransformation, use the RGB/K option and pull the background point down to where you want it.  I generally prefer ~0.08.

Now *remove* the mask inversion.  Now you're working on the starless image but only the galaxy.
Adjust galaxy saturation to your liking under Curves Transformation.
Using the HDR Multiscale Transform tool to prevent core blowout and enhance the dust.  On this, I generally put the checkmarks on "to lightness" and "lightness mask" and select 5 or 6 layers and then play around with the "overshoot" function until it looks right.  Very trial-and-error.
I then do *some* unsharp masking.  Typically use something less aggressive than the default settings.

Using Pixel Math with the above image names, the expression is simply:
glow+stars
I usually name it something like, "combined" for the output image, but to each their own.

Hope this helps.

Clear Skies,
Phil

andrea tasselli:
Yes, you got that right. When imaging at full broadband, as you are wont to do, than the issues with doublets can come back and bite you. If you were imaging with NB filters than the issues would be lessened and so if the image scale was more in keeping with capability of 80mm scope. To be honest I'd have already bought me a TS 6" f/4 Newt and be done with it since it is small and light enough to go with your existing mount.

Yep, I'm gonna go for a 6" Quattro soon for my CEM25P, pretty positive it will run on it without issues as my guiding leaves headroom, 2 more kg with another 2kg CW shouldn't be an issue. and in the long term I plan a bigger newt and a bigger mount.

Phil Creed:
I dunno.  Did you have any thin cirrus passing through during imaging?  That might cause some haloes.

I think something might have gone awry in the processing.  I shoot from a Bortle 6 so if anything, my skies are worse.  But for reference, I got this after 3 hours on a somewhat moonlit night:

https://www.astrobin.com/a3tu2v/

Similar speed (f/5.4 vs. your f/5.6) and somewhat similar focal length (540mm vs. your 450mm)

So something tells me it's the processing, not the data...which isn't the worst thing.  Precisely the opposite, because if the underlying data is good, it's very fixable.

The data looks a bit "flat", with some loss of contrast particularly around the spiral arms.  On the plus side, the cores aren't blown out and the dust detail near the center of both NGC 5195 and M51 look nice.

If it helps, here's my general workflow for a OSC camera:

Stack in Deep Sky Stacker (yes, DSS.  I'm THAT "old-school"...)
Dynamic Crop
DBE
BlurXTerminator, default settings
Photometric Color Calibration (can't get SPCC to work for some reason)
NoiseXTerminator, 0.70 overall / 0.15 on details
Histogram transformation (can't get GHS to work, either) until the histogram peak is ~0.20
NoiseXTerminator, ~0.50 / 0.15 (less aggressive round, if needed at all)

Then the "fun begins":

Rename image to "glow"  (or whatever suits you)
Starnet++ V2, rename stars-only image "stars" (or something else)
Adjust color saturation on "stars" image, set it aside.

"Glow" image:
Extract Luminance channel
Using Histogram transformation, slightly stretch it and then clip (yes, clip) the left side until ~45% to 50% of all pixels are clipped.  Use preview if necessary.
Select the newly-created luminance mask but *invert* it and find the general background illumination (mine's often ~0.20 to 0.24).
Using Curvestransformation, use the RGB/K option and pull the background point down to where you want it.  I generally prefer ~0.08.

Now *remove* the mask inversion.  Now you're working on the starless image but only the galaxy.
Adjust galaxy saturation to your liking under Curves Transformation.
Using the HDR Multiscale Transform tool to prevent core blowout and enhance the dust.  On this, I generally put the checkmarks on "to lightness" and "lightness mask" and select 5 or 6 layers and then play around with the "overshoot" function until it looks right.  Very trial-and-error.
I then do *some* unsharp masking.  Typically use something less aggressive than the default settings.

Using Pixel Math with the above image names, the expression is simply:
glow+stars
I usually name it something like, "combined" for the output image, but to each their own.

Hope this helps.

Clear Skies,
Phil

Pheww, hard to say about the cirrus - I was inside and let the mount run it's job, as it's on my roof terrace and it sadly has wooden flooring, so my guiding doesn't like me running around and checking the sky...

Our linear processing looks pretty similar, except that I didn't do much noise reduction in the linear state.
The Non-linear processing looks interesting, might give it a try on the weekend when I have the time for it Very helpful, thanks, always interesting to see what others do with their data!

I was pretty content with the pure stretching itself, but otherwise it's a bit tricky... :/

andrea tasselli:
Right off the bat you have a very sweet flat background, so nothing to complain about it. And very little data depth, as expected. Might I suggest you start using PI for pre-processing too?

Very little data depth -> too short of a total exposure? Or would you suggest longer subs? I can easily take longer ones, mount isn't the issue, but I fear too much light pollution, so I keep it at 120-180 seconds, depending on how bright the target is.
Yeah, I eventually wanted to start using PI for pre-processing, but I haven't come around to truly try it - again, on the weekend I could give it another try.


CS

I am by no means a master of PI....yet. 

I looked at your data to see what I could do with it. 
It was interesting for me to see your data, as I am currently imaging only with a DSLR and am very challenged with noise etc. in my images. 

You can see my result here - https://astrob.in/6a84wa/0/

I will naturally delete it when you say so again - it's not made public. 

My process was:

• starXterminator
• DBE (remove large gradients as per Adam Block here: https://www.youtube.com/watch?v=7ldbGxFi-OM)
• DBE again in starless image
• Add images together again with PixelMath
• SPCC
• EZ Soft Stretch
• BlurXTerminator

var P = new BlurXTerminator;
P.ai_file = "/Applications/PixInsight/library/BlurXTerminator.2.mlpackage";
P.correct_only = false;
P.correct_first = false;
P.nonstellar_then_stellar = false;
P.lum_only = false;
P.sharpen_stars = 0.30;
P.adjust_halos = -0.25;
P.nonstellar_psf_diameter = 0.00;
P.auto_nonstellar_psf = true;
P.sharpen_nonstellar = 0.90;

• Extract L
• LRGBCombination with L to saturate RGB image (2 times with saturation set to 0.310 and 1 time with saturation to 0.310 AND Chrominance noise reduction)
• RangeSelection to create mask of galaxy
• add to L layer and protect all BUT galaxy
• use HDRMultiscaletransform  and then LocalHistogramEqualization to sharpen galaxy core - test different variations etc.
• apply L layer back on RGB with RangeSelection and all settings default.
• From extracted L layer create starmask again (once the mask is created in a new file - add the stars back to the L layer again (back arrow on the L view))
• Make stars slightly bigger (MorphologicalTransformation)

  /*

* Start time: 2023-04-25T20:22:03.987Z UTC
* Execution time: 208.970 ms
*/
var P = new MorphologicalTransformation;
P.operator = MorphologicalTransformation.prototype.Dilation;
P.interlacingDistance = 1;
P.lowThreshold = 0.000000;
P.highThreshold = 0.000000;
P.numberOfIterations = 1;
P.amount = 1.00;
P.selectionPoint = 0.50;
P.structureName = "";
P.structureSize = 5;
P.structureWayTable = [ // mask
[[
0x00,0x00,0x01,0x00,0x00,
0x00,0x01,0x01,0x01,0x00,
0x01,0x01,0x01,0x01,0x01,
0x00,0x01,0x01,0x01,0x00,
0x00,0x00,0x01,0x00,0x00
]]
];

• Convolution on starmask

• var P = new Convolution;

P.mode = Convolution.prototype.Parametric;
P.sigma = 5.30;
P.shape = 2.00;
P.aspectRatio = 1.00;
P.rotationAngle = 0.00;
P.filterSource = "";
P.rescaleHighPass = false;
P.viewId = "";


• Invert L view
• Pixelmath Inverted L view with Starmask in new file
• Invert this new file and add it as mask to the RGB image.
• This should give you a mask where ONLY the galaxy is not protected.


• Unsharp mask on the image with inverted mask on
• NoiseXTerminator

That is the workflow I experiment with.

I hope it gives you some inspiration.

My own attempt on M51 has until now - approx 10 hours of exposure on the target
https://www.astrobin.com/ose1mc/

Very similar workflow as described above.

I'll hopefully make this simple.

Yes, more is possible….  

Generally speaking OSC data takes a huge hit in the red and blue channels due to efficiency passing through the Bayer matrix.   Because most Bayer matrices are RGGB, you are going to get a ton of green long before the red and the blue come in.  (this is why mono is much more preferred for astrophotography).   

What does this translate to?     Noise.   Lack of signal.  

Compared to someone using a mono camera and gathering the same amount of integration time, you're only gathering ~30%.         Your image needs more integration time to fully pop.    If you look at your linear stack in Pixinsight and cycle through the red, green, and blue channels individually you will see exactly what I'm talking about.  


Also, you're using a 183, which unfortunately is not nearly as efficient as today's cameras.     

Judging by your final image, I think you still had some images with clouds in them.   

Overall, I think your image looks just fine for the quality of gear you have and the integration time involved.

Oh, and reading through the comments about aperture size….   I think it has less to do with size, and more the quality of the optics.

I'll hopefully make this simple.

Yes, more is possible....  

Generally speaking OSC data takes a huge hit in the red and blue channels due to efficiency passing through the Bayer matrix.   Because most Bayer matrices are RGGB, you are going to get a ton of green long before the red and the blue come in.  (this is why mono is much more preferred for astrophotography).   

What does this translate to?     Noise.   Lack of signal.  

Compared to someone using a mono camera and gathering the same amount of integration time, you're only gathering ~30%.         Your image needs more integration time to fully pop.    If you look at your linear stack in Pixinsight and cycle through the red, green, and blue channels individually you will see exactly what I'm talking about.  


Also, you're using a 183, which unfortunately is not nearly as efficient as today's cameras.     

Judging by your final image, I think you still had some images with clouds in them.   

Overall, I think your image looks just fine for the quality of gear you have and the integration time involved.

Oh, and reading through the comments about aperture size....   I think it has less to do with size, and more the quality of the optics.

It's certainly a possibility I have clouds - at some point, the sky turned fully cloudy, I rejected the worst images according to APP's rating mechanism anyways, but I didn't look at them all individually, to be honest... Now I'm curious what makes you think that, how you spotted that. I realised while stacking that some pictures good a worse quality ranking than others - about a third of the best value - althought, the FWHM wasn't bad, and the guiding / seeing generally constant, so you might be on to something - I might want to go through the subs individually.

Regarding the Mono vs OSC: thanks for explaining, makes sense. I didn't know it was only 30%, that's... rough. I'm eyeing going mono eventually anyways, I can't justify it now, as I want to upgrade my scope first, but next is probably the camera, maybe a 294MM if the 183MM isn't efficient enough... not the biggest fan of the square sensor of the 533MM personally, sadly.

Well, I sometimes feel like I'm hitting the limits of my imaging train, which is starting to annoy me - of course, my post processing isn't perfect, but when the S/R is right, the final result looks better, eg my M31, or the pacman nebula...
The doublet I use has a lot of CA in my opinion, if I don't realign the channels, I have purple fringes on a lot of stars when I pixel peep. After all, it is a 550€ chinese doublet...

Usually any time the stars show up with a fuzz around them, it's either clouds or you dewed up.    Those aren't halos IMO.   

Use Blink process in pixinsight and you can speed through each sub and watch how your seeing improved or worsened throughout the night.   You should be able to see when it got cloudy and reject better.   

This hobby is a money pit.    I'd stay away from the 294MM, it has its own subtle issues. Not that it's a bad camera tho, and those tiny pixels can be nice at times... 533/2600/6200 all have great performance and no amp glow.  

Sounds like you'll end up just like me.  I started this hobby last August with a nearly identical setup.   Within about a month I went full ham.

The data looks good to me; the background is smooth. I understand that you are amazed by the faint halo of M51 and want to make it more visible (all M51 fans want that ). For that you definitely need more integration time. My initial guess for the weird halos was the complicated workflow. Unfortunately I don't have the time to process it by myself but my workflow would be similar to  @SemiPro (but using Nikita's tools and deconvolution instead), plus more saturation to the galaxy.

Congrats to you and to @SemiPro! RCC posts like this are truly educative!