StarTools

If you put the single sub you uploaded through dcraw like so;

dcraw -T -4 -o 0 -r 1 1 1 1 IMG_4108.CR2

You will obtain what a stacker does/uses internally (provided it is configured correctly).

In terms of luminance, the resulting frame looks virtually identical to the stack - plenty of stars visible (flat frame correction not withstanding of course).

So many stars visible in your linear data may or may not be a problem in some instances, depending on whether your camera's sensor response is truly linear, even when approaching saturation (it can affect deconvolution's effectiveness for example). Right now though, you probably have bigger fish to fry than worrying about that.

In terms of coloring, however, things look a bit different;

IMG_4108.jpg (105.94 KiB) Viewed 5471 times

This is pretty close to the expected color signature for a modded camera or OSC.

In contrast, your current full stack appears color balanced somehow, with the strong red response quite evident;

post-194246-0-93942400-1608425994.jpg (140.55 KiB) Viewed 5471 times

Ergo, something is meddling with your coloring, which - at the end of the day - is a fairly minor problem and comes down to just changing a setting somewhere. Otherwise, comparing the single frame and the stack, shows good calibration and a nice, flat field. You use the right ISO for your camera and doing a lot right.

The lens you are using is probably the weakest link in your optical train right now. Lenses meant of terrestrial use, exhibit chromatic aberration that is (depending on your standards of course) often not acceptable for AP goals. Chromatic aberration will manifest itself in blue or purple rings of color. They can be processed out however. Worse, though, some/most stackers will have trouble aligning stars and color channels properly, resulting in color fringing of stars (as is the case here), while some stackers can wholesale introduce aberrant color information themselves (as is the case here as well) if not configured properly;

Selection_406.jpg (3.33 KiB) Viewed 5471 times

(an overexposing core should obviously not have a color like this)

In such case, color preservation through something like StarTools' "color constancy" mode will readily reveal the aberrant color information. Again, there are several techniques to hide the problem (using the Highlight Repair feature in the Color module is a good start). You can also decide to not use the Color Constancy mode (again, this is hiding the problem and not a "solution" as such). Stopping down your lens can also help mitigate some of the worst chromatic aberration. EDIT: FWIW, AutoDev counters stellar bloating, so using it, particularly in your case is highly(!) recommended.

Chromatic aberration also bloats stars in the luminance domain, causing stars to quickly take over from any larger scale nebulosity. In widefields like these, that quickly becomes a serious problem. You can use ST's Shrink module or PI's morphological transform for stellar profile manipulation, and/or ST's Super Structure module or PI's wavelet transform to manipulate the larger scale structures vs small stuff like the stars, in order to mitigate the problems with the stars.

To top off the cascade of "problems", is the fact that you're not guiding, which causes stars, which already have obnoxiously large stellar profiles due to the chromatic aberration, to "smear around".

All said and done, you're well on your way - it's all tweaks to your acquisition and software settings, and learning how to work around any left-over issues inherent to your gear. Let us know how you go!

TL;DR Data.

A quick process in StarTools with mostly defaults where possible, taking into account all the observations of my previous post;

Workflow as follows;

--- Imported with first option (linear) as this dataset appears to be already color balanced.

--- Auto Develop

To see what we got. See previous post for some observations.
--- Bin

This makes the tracking error and color fringing a little less obvious. It improves signal as a bonus, but really, it is quite strong as-is.
Parameter [Scale] set to [scale 50.00% / +2.00 bits / +1.41x SNR improvement]
Image size is 2744 x 1834

--- Crop

Get rid of some stacking artifacts.
Parameter [X1] set to [11 pixels]
Parameter [Y1] set to [16 pixels]
Parameter [X2] set to [2736 pixels (-8)]
Parameter [Y2] set to [1819 pixels (-15)]
Image size is 2725 x 1803
--- Wipe

Defaults.
Parameter [Dark Anomaly Filter] set to [4 pixels] just in case - the image is very busy and I am finding it hard to see any dark pixel clumps that don't belong...
--- Auto Develop

Defaults. No RoI.
--- Color

Legacy preset, which mimics the way old/conventional software desaturates highlights as chrominance information is stretched along with the luminance.

Default color balance was used. What we're ideally after - even with a modded camera - is a good representation of all stellar temperatures. Red->orange->yellow->white->blue. That is how you know you got a good color balance. All stars should have a color when you zoom in. When using the Legacy preset, the color will be subtle due to the desaturation but it should nevertheless be detectable. The H-alpha is obviously red, tending to pink due to other bluer emissions and/or reflections that almost always are also present. Green is a very rare color in outer space (notable exception O-III dominant areas such as M42's core), so if you are absolutely sure your color balance is otherwise good, then any leftover green can be booted using the Cap Green parameter.
Parameter [Cap Green] set to [100 %] to get rid of any spurious green
Parameter [Highlight Repair] set to [Off], as the oldschool desaturation trick/limitation was enough to hide the issues with chrominance information in the highlights.
--- Shrink

As said in my previous post, taming the star field can really help with widefields like these. Complete removal of some (or all) stars is IMHO not OK if you're doing documentary photography. Some even find shrinking them objectionable, but IMO it can really help images like these, particularly if you avoid complete removal of the dimmer ones, and - of course - avoid artefacts.

Auto Mask.

Parameter [Halo Extend] set to [0 pixels] (no need to grow mask which is already very busy).
Parameter [De-ringing] set to [Off] (only really needed when decon was used)
--- Super Structure

Saturate preset (you can try the others too obviously).

The Ha nebulosity is the star of the show here, and this is an easy way of emphasizing it without performing (frowned upon) manual selective processing. As said, you can also use the Entropy module here.

Parameter [Airy Disk Radius] set to [11 %] to match field of view (smaller stars)
Parameter [Saturation] set to [100 %] to moderate the effect a little.


No noise reduction applied. Tweak the defaults to taste obviously - this is just a quick run-through.


Again, it's preferable if you can fix the acquisition/optics and stacking issues (tracking, chromatic aberration, color balancing) so there is less to work around and worry about, but you're well on your way!