Some Stars

[decay]

Hi all,

Well, not sure if it's worth sharing, but in the end I kind of like this image:

The stars are a bit elongated, but I think I now found out what sometimes causes collimation problems: It seems that when it's very cold outside, the holder of the secondary mirror becomes a bit loose. Will have to think about it.

Even worse, the stars show the 'dark eye' pattern (dark dots in their center) we already discussed some time ago:

2025-02-25 20_50_18-M44 - Praesepe (The Beehive Cluster) (decay) - Volle Auflösung _ AstroBin – Mozi.jpg (2.56 KiB) Viewed 10467 times

This is visible right from the beginning after the first OptiDev stretch. I'm not sure if this is a stacking related problem; of course the stars are saturated, but I don't see anything too bad :

2025-02-25 20_59_55-Fitswork.jpg (16.08 KiB) Viewed 10467 times

As for processing with ST: A very aggressive Wipe (Uncal 1 preset) due to strong gradients. But it did no harm to the stars. OptiDev with reduced Shadow Linearity (15 %). No Contrast, no HDR, no Sharp. SV Devon, only 5 Sampled Iterations. No Shrink, no Super Structure. NR with highly increased Grain Size (12 px) and Grain Dispersion set to 4 px. FilmDev with Skyglow set to 4%.

Oh, and was able to resist to use StarNet++ to produce a starless version to do a separate stretch. Haha, old joke, but more relevant than ever before. No?

Best regards!

Dietmar.

Edit: AstroBin link: https://www.astrobin.com/qzdavj/

[dx_ron]

Quite worth sharing (it's called STAR Tools, after all!). I'm shooting ~ 1/2 hour of an open cluster (the Broken Heart Cluster) right now, while I wait for full darkness.

I think your stars look lovely. The nicely saturated cores and diffraction spikes give them a great look. Your aggressive reduction of the background makes for lovely stars, but there are a number of distant background galaxies hiding behind the Beehive (difficult to bring out, though).

In optidev, did you increase the bit depth? Going just for stars, I would go ahead and use the full bit depth of your sensor.

[decay]

Thanks for your reply, Ron. I think I tried changing the bit depth, but it made no difference, surprisingly.

Some of the background galaxies are already visible (and I like them), but a less aggressive stretch always resulted in a dirty looking background, so I called it a day. But I already thought about restacking with Siril and to use its background-extraction-per-frame feature. Maybe this helps to go away with a less aggressive stretch in ST itself. I think your comment convinced me to give this a try.

Good luck for your project. No darkness here. Only clouds.

Dietmar.

[dx_ron]

I'll toss some stars in here, too. Maybe we can make this a generic open cluster thread...

In this case, I used some time while waiting for proper astro darkness to image a semi-randomly chosen open cluster, NGC 2281 (the "Broken Heart" cluster). 45 minutes total from two consecutive nights.

NGC_2281_89x30s_v3.jpg (434.52 KiB) Viewed 3270 times

It's got nowhere near the "pop" of Dietmar's Beehive. Maybe processing? Definitely my severe lack of diffraction spikes! Maybe also the fact that only one star in the field is as bright as the main stars in M44. But maybe I'll go back and try to add more zip and zest.

[decay]

Generic open cluster thread is a great idea.

Indeed ironically, everything which makes look the Beehive nice in this case are undesired effects under normal circumstances. Enlarged stars and surrounding glow due to atmospheric conditions (seeing, haze), limited aperture, optical imperfections like dirty or damaged optical surfaces and obstruction. And of course spikes.

So your image is simply too perfect! Superior optics and perhaps better conditions. I’m not sure whether more integration time will help in this case. My intention in gathering more integration time was to get a more pleasing background and maybe to catch some of this nice little galaxies.

If you like, you could try to replace the imperfections by artistic post processing steps. The Super Structure module was called Life module in preceding versions of StarTools. If I remember correctly, there was a preset “Glow” or similar which brought back – well – glow to the stars. And it worked very well. Maybe that’s still possible with Super Structure (by using the Airy only preset somehow?), but I haven’t tried until now.

And there is a digital processing technique / filter called Orton Effect, which some folks use to bring in some glow (sorry if I’m constantly telling you things which you probably already know).

I already was thinking about all this, when I imaged the Double Cluster as a parking target, inspired by Stefan. If you compare our images, Stefan’s image looks much more pleasing, but I’m not sure, why?

https://app.astrobin.com/u/Boex?i=050lne#gallery
https://app.astrobin.com/u/decay?i=n7gq5b

Dietmar.