Best-looking stars? [Deep Sky] Processing techniques · Emmanuel Valin · ... · 68 · 3518 · 7

In my quest to keep improving my images, I’d like to ask the AB community for examples of deep-sky images you find have some of the best-looking stars.

Next step will be about understanding the gear / acquisition & processing techniques that can produce such results, but my first objective is to actually find some images that display top-notch stars according to you.

Of course highly subjective, but that’s what makes it fun !

CS

Emmanuel

With newts, these are my favorite type of stars https://www.astrobin.com/dosgf6/J/

And I think these are my favorite, for refractors https://www.astrobin.com/t4ymfz/

That Newt, my friend. Is a CDK.

With newts, these are my favorite type of stars https://www.astrobin.com/dosgf6/J/

And I think these are my favorite, for refractors https://www.astrobin.com/t4ymfz/

That Newt, my friend. Is a CDK.

Oooooh 


I guess I meant that's how I like stars that have diffraction spikes.

I don't mind em, or like em.

AstRobert:
I really love these stars here:
https://www.astrobin.com/ahxx7q/?q=Charles%20Hagen

I am actually looking for tips on how to process stars to have nice colors. All of these pictures with amazing stars have extremely long exposure times and i wonder how they manage to not totally destroy the star colors with that. Are you aware of good tutorials for amazing star colors!?

Cheers, Robert

They aren't necessarily all that long, considering apertures and pixel sizes. Under dark skies, with small pixels and narrow band filters it is not unusual to need and benefit from longer exposures. At 300 seconds, just 5 minutes, that is not really all that long. If you had huge pixels, then yes, you might saturate, but with small pixels the stellar signals should be getting distributed over many pixels. 

I have used 10 minute exposures with an f/4 camera lens with a 150mm aperture using narrow band filters, and 2.4 micron pixels. I would usually clip half a dozen to a dozen of the brightest stars, just a smidge. Based on my analyses at the time, the next brightest stars would have allowed another 180-300 seconds of exposure before clipping.

AstRobert:

Jon Rista:

AstRobert:
I really love these stars here:
https://www.astrobin.com/ahxx7q/?q=Charles%20Hagen

I am actually looking for tips on how to process stars to have nice colors. All of these pictures with amazing stars have extremely long exposure times and i wonder how they manage to not totally destroy the star colors with that. Are you aware of good tutorials for amazing star colors!?

Cheers, Robert

They aren't necessarily all that long, considering apertures and pixel sizes. Under dark skies, with small pixels and narrow band filters it is not unusual to need and benefit from longer exposures. At 300 seconds, just 5 minutes, that is not really all that long. If you had huge pixels, then yes, you might saturate, but with small pixels the stellar signals should be getting distributed over many pixels. 

I have used 10 minute exposures with an f/4 camera lens with a 150mm aperture using narrow band filters, and 2.4 micron pixels. I would usually clip half a dozen to a dozen of the brightest stars, just a smidge. Based on my analyses at the time, the next brightest stars would have allowed another 180-300 seconds of exposure before clipping.

Well I was looking at the RGB exposure times without NB Filters (cause thats a whole other topic regarding star colors ;-) and I get saturated star cores at 120sec with an F7.5 Scope so that is why I wondered, how these great stars colors with 600s at f4 or whatever come to be.

FWIW, 600s @ f/4 is with 3nm narrow band filters, not broadband filters. I definitely couldn't get 600s exposures with RGB. Some of the images had 1200s exposures with narrow band filters. The RGB filters were 300s, which is only about double and change what your 120s. To that...

It will also depend on your gain. People usually use very high gain settings these days. Sometimes, if the camera has a high conversion gain (HCG) mode, then you might only lose a fraction of a decibel of dynamic range, which won't matter. Yes, you'll need to use shorter exposures, but with read noise as little as 1.2e-, then you truly don't NEED long exposures. A lot of cameras that have HCG modes, have identical (or slightly higher) dynamic range at minimum gain, which means you should be able to use even longer exposures at gain 0, integrate fewer subs, but end up with the same results in the end...if you really wanted longer exposures/fewer subs/good star color. 

On the other hand, a lot of cameras don't have an HCG mode, and higher gain settings are going to diminish your dynamic range by stops. THAT could be part of the problem. If you want the maximize your star quality, then technically speaking you should be using the camera at the gain setting that just gets you to the maximum dynamic range. In some cases, that is the lowest gain setting, other times it might be higher than minimum gain, but lower than other commonly used settings like unity gain or "lowest read noise." 

Another thing to ask yourself is, how many stars ARE saturating? Ten, twenty? If so, then that is a tiny fraction of the overall star count in most images, and it is really not going to matter if the cores of some stars clip like that. In fact, the way stellar saturation distributes in most images...if you saturate 10 stars at say 120s, you are probably only going to saturate about 15-20 or so at 240s. Depends a lot on the field, but the brightest stars are often SIGNIFICANTLY brighter than the vast majority. So you don't necessarily go from clipping 10 stars at a couple of minutes, to clipping all of them at five minutes...if you choose to increase your exposure length. A lot of the time, you can more than double, or even triple, your exposure and the number of stars that clip will only increase by a small amount. 

Alternatively, if you are saturating MOST stars in just 120 seconds, I would really want to figure out why, as that generally shouldn't be the case... One possibility could be a gain well above the optimal gain for maximum DR. It may also just be that you are using an HCG mode on your camera, and you simply shouldn't be aiming for long exposures (generally speaking, the HCG mode IS optimal, but it will require acquiring lots and lots of shorter subs and stacking a ton of them, to maximize the benefit...which, really, IS the benefit: very high efficiency! ;))

I guess if you have ridiculously high light pollution, then that might add a significant background offset that could push more stars to clipping. If that is the case, then sadly, your problems with star color are probably not just a matter of saturation, but also pollution. I could never get good star color under light polluted skies, no matter what I tried (LP filters, gapped RGB filters+mono, OSC, etc. etc.) A lot of the time, I think people just think of light POLLUTION as just "the gradient" and that it can be removed without issue, however its a signal pollutant, and is often not just a simple gradient, and it contains a lot of color information as well...and that can certainly muck with star color. IF you then throw LP filters into the mix, then you might as well just forget about quality star color.

@Emmanuel Valin Well, it might take some time to find "the best" stars...that is a relatively rare occurrance. 

To continue the discussion though, just picking an image off the home feed that I liked at least one aspect of the stars from:

https://www.astrobin.com/full/fdynpn/0/

The diversity of stellar sizes here, IMO, is an important trait. I come across a lot of images these days where the stars have been reduced and diminished so much, that most look like tiny pixel-sized points of light. That loses an aspect of stars that I think is important...relative size and relative distance. With stars of varying size, of NATURAL sizes, you maintain a certain sense of the three-dimensional distribution of the stars in the field. 

The above stars are not perfect. I think they are a little lacking in color. Another attribute of "best" would be how round they are, and I think that is often a hard thing to achieve, without also normalizing their sizes...AI powered star reduction will often normalize size, even if it improves roundness, so while the stars may be more aesthetically pleasing from a form standpoint, personally I feel if you lose the natural differences in size you lose that sense of depth and dimension in the starfield itself.

Tony Gondola:

Jon Rista:
@Emmanuel Valin Well, it might take some time to find "the best" stars...that is a relatively rare occurrance. 

To continue the discussion though, just picking an image off the home feed that I liked at least one aspect of the stars from:

https://www.astrobin.com/full/fdynpn/0/

The diversity of stellar sizes here, IMO, is an important trait. I come across a lot of images these days where the stars have been reduced and diminished so much, that most look like tiny pixel-sized points of light. That loses an aspect of stars that I think is important...relative size and relative distance. With stars of varying size, of NATURAL sizes, you maintain a certain sense of the three-dimensional distribution of the stars in the field. 

The above stars are not perfect. I think they are a little lacking in color. Another attribute of "best" would be how round they are, and I think that is often a hard thing to achieve, without also normalizing their sizes...AI powered star reduction will often normalize size, even if it improves roundness, so while the stars may be more aesthetically pleasing from a form standpoint, personally I feel if you lose the natural differences in size you lose that sense of depth and dimension in the starfield itself.

When you talk about size I hope you understand that what you are seeing are differences in brightness, for the most part, not distance.

It is interesting why some would have a different definition of what best stars means. For myself that can vary. Sometimes I don't remove the stars because I want to reserve that relationship you talked about. Then again, if you had imaginary optics that defied the wave nature of light and pixels didn't bloom then each star would in fact be a single pixel. I guess that means for me at least that there isn't a single answer to the question, it just depends on what serves the photographer best in the expression of the image.

I do (hence why I put relative size before relative distance), although distance affects brightness to a degree as well (light falls off over distance). So yes, technically, differences in brightness, but to a degree that is also differences in distance.  

Undoubtedly, everyone will have a different opinion. FWIW, when you look up at the night sky, not every star is the same. You can see differences...color, size (or brightness, but it kind of looks like size to the naked eye even). I think those differences are important, rather than diminishing them to nearly nothing.

Not to plug my own image super hard but I've really taken a liking to how I did the stars here: https://app.astrobin.com/u/ThisIsntRealWakeUp?i=3i5tls

Big, glowing stars are coming back in fashion if you ask me. Not to be confused with bloated or egg-shaped stars. But you can use blurx to increase the star glow while still correcting their shape and I think it yields a nice result.

AstroÅmazer:
Can you please critique my stars here? 

https://app.astrobin.com/u/Astro%C3%85mazer?i=hp2izo#gallery

I think I need some step-down rings. I have tried this lens-camera combination at HCG and more than 25% of the stars are getting clipped.

Even at Gain 0, I don't like how soft everything looks.

I used minimal deconvolution and some GHS based arcsinh transformation in Siril.

Thanks in advance.

Looks like it could be a few things:
1. You are a bit out of focus
2. Why gain 0?
3. You made your background too dark. IMO space looks best when it's a dark dark grey, not black.

AstroÅmazer:
Can you please critique my stars here? 

https://app.astrobin.com/u/Astro%C3%85mazer?i=hp2izo#gallery

I think I need some step-down rings. I have tried this lens-camera combination at HCG and more than 25% of the stars are getting clipped.

Even at Gain 0, I don't like how soft everything looks.

I used minimal deconvolution and some GHS based arcsinh transformation in Siril.

Thanks in advance.

Everything just looks to soft to my eye, almost like it's slightly out of focus.

AstroÅmazer:
Can you please critique my stars here? 

https://app.astrobin.com/u/Astro%C3%85mazer?i=hp2izo#gallery

I think I need some step-down rings. I have tried this lens-camera combination at HCG and more than 25% of the stars are getting clipped.

Even at Gain 0, I don't like how soft everything looks.

I used minimal deconvolution and some GHS based arcsinh transformation in Siril.

Thanks in advance.

The biggest factor that stands out the most, is the softness of the stars. Initial thought is that looks like a bit of defocus, however it is also possible your seeing is just horrendus...I've had periods where seeing was so bad I couldn't help but get soft stars (which, further, makes it that much harder to focus in the first place, so its usually a combination of the two if you do have ultra bad seeing.) 

Examining more closely, it looks like there may be some tilt, as the stars in the upper and lower right exhibit some coma, and maybe other optical issues. If you can dial in your focus better, any characteristics of these aberrations should become clearer. Fixing the tilt would be next after figuring out how to dial in your focus. If you cannot actually focus, then you might have a spacing issue as well, and you would need to resolve that first. 


A thought on the f-ratio... With modern cameras like the one you are using as low noise as they are, I wonder at the real utility of f/2.8. Sometimes ultra fast apertures just present more problems than they solve. You might well want to try some step down rings, and see if a slightly slower aperture, f/3, f/4, simplifies things. Sometimes more simplicity is worth the tradeoff of speed.

Jon Rista:

AstroÅmazer:
Can you please critique my stars here? 

https://app.astrobin.com/u/Astro%C3%85mazer?i=hp2izo#gallery

I think I need some step-down rings. I have tried this lens-camera combination at HCG and more than 25% of the stars are getting clipped.

Even at Gain 0, I don't like how soft everything looks.

I used minimal deconvolution and some GHS based arcsinh transformation in Siril.

Thanks in advance.

The biggest factor that stands out the most, is the softness of the stars. Initial thought is that looks like a bit of defocus, however it is also possible your seeing is just horrendus...I've had periods where seeing was so bad I couldn't help but get soft stars (which, further, makes it that much harder to focus in the first place, so its usually a combination of the two if you do have ultra bad seeing.) 

Examining more closely, it looks like there may be some tilt, as the stars in the upper and lower right exhibit some coma, and maybe other optical issues. If you can dial in your focus better, any characteristics of these aberrations should become clearer. Fixing the tilt would be next after figuring out how to dial in your focus. If you cannot actually focus, then you might have a spacing issue as well, and you would need to resolve that first. 


A thought on the f-ratio... With modern cameras like the one you are using as low noise as they are, I wonder at the real utility of f/2.8. Sometimes ultra fast apertures just present more problems than they solve. You might well want to try some step down rings, and see if a slightly slower aperture, f/3, f/4, simplifies things. Sometimes more simplicity is worth the tradeoff of speed.

Step down rings was my first thought. But now that you mention it, there could be tilt in the imaging train. I am using a ZWO filter drawer which takes the F mount lens on one side and the ASI585 on the other. The whole train is mounted on the ZWO 78mm ring holder for the camera. Not the most robust setup.

I can try adding some shims between the filter drawer and the camera and see if that helps with focusing too. Thanks.

@Oskari Nikkinen  gets really nice stars with his ONTC newt