m101

[alacant]

Hi everyone

New moon so of course the conditions were rubbish with easterlies creating the usual haze as the night air cooled. Anyway, no excuses. Three telescopes, 4 guys with an assortment of miners' lamps, torches, laptop screens, cheap supermarket beers and cables. Everywhere. I was in charge of the f4 and actually got to take some frames.

As always, colour remains elusive; there seems no right or wrong way of doing it. 

So, and against all the odds, here is a photograph of a galaxy.

Do say what you think and post your dslr version. You can learn so much by comparison:)

700d @ ISO800

 

Edited February 23, 2020 by alacant
wrong flat frames

[Pankaj]

Super shot. Thousand times better than what I got with my dslr on 13pds, last year.

[MarkAR]

Well done, lovely image.

[ollypenrice]

It's deep, with the faint outer arms showing. It's very well resolved. The background sky is neither too dark nor too smooth so the black point has been nicely judged.

It does lack colour, as you say. There are two Ps techniques which might be available in GIMP, I don't know. 1) Make three layers. Set top to blend mode Soft Light and flatten onto second layer. Set second layer to blend mode colour and flatten.  2) Convert the image to Lab colour mode and greatly increase the contrast in a and b channels by the same amount. These are less noise-inducing than using Saturation.

It looks as if your flats have very slightly over-corrected. You could fix this in Curves. Put in fixing points at and above the brightest part of the background and slightly lift the curve below them.

Olly

[alacant]

4 minutes ago, ollypenrice said:

flats

Done.

Cheers

[ollypenrice]

😁lly

[alacant]

'Linux makes better louder bells'.

I'm sure @vlaiv would approve:)

Edited February 23, 2020 by alacant

[vlaiv]

@alacant I think you've been asked this before, but here it is again: Why do you post your images in Getting Started with imaging?

Image such as above, in my view, should certainly be posted in main imaging section.

Now onto the criticism of the image - background again . In my view improvement on clipping, but maybe a bit too bright this time? Also, I think you are pushing data beyond what it can deliver - background is too grainy at this level of stretch. I do understand the need to show every bit captured in the image, but M101 is very low surface brightness target and good SNR is important if you are going to try to show every last faint bit in spiral arms. If you don't have the SNR - you need to make effort not to over do the stretch (at least it is effort for me - I always have to make conscious effort not to stretch too much).

@ollypenrice

What's with hue in that image / screenshot? Do you have some sort of color profile enabled in PS or something else? As far as I can tell - you opened above image to analyze histogram so it should be the same image, but to my eye and on my computer screen, two images are distinctly different in color - not sure if it will be seen by others as it might be issue with my computer, but here it is:

Left - your screen shot, right, original image. Maybe you did a bit of curves and levels and made hue different?

In the end, here is my tweak to the image, hope it's ok to do this - background made a bit darker and a bit of noise handling:

First histogram - to verify it is bell shaped and nice:

and image (red has been touched a bit to make background a bit more neutral / gray):

[alacant]

8 minutes ago, vlaiv said:

Getting Started with imaging

Hi

Here you get feedback.

 

[alacant]

@vlaiv

OK. If I go darker than this, I find I begin to lose the arms of the spiral. I also did a bit of denoise.

Cheers and thanks for your patience.

[vlaiv]

Just now, alacant said:

OK. If I go darker than this, I find I begin to lose the arms of the spiral.

Yes, I know - you can't render something that has lower SNR in the image if you want to avoid the noise and similarly if you bring out the faint stuff and you don't have enough SNR you will bring out the noise.

That is what I wanted to point out - In my view, good astro image will have some noise, so it won't be completely noise free. Noise just needs to be fine grained enough and controlled enough so it does not distract from the image. On the other hand, I don't think that image looses much if you don't bring out every possible detail at expense of blowing out noise. If you can't fully render arms without making background too noisy - you have two options:

1. Just don't try to get those arms bright and visible and settle for what you have captured well

2. spend more time on target until you have enough SNR on each thing you want to render.

Problem with approach 2 is that you are never going to be fully satisfied - more you spend on target, more faint stuff you reveal and want to get good SNR of and then you spend some more time on target and reveal more faint stuff and go in circles

 

[Xplode]

Pretty good image with some small things you want to look into.

Your collimation is off as can easily be seen in the lower left corner, it's of course nothing you can do about it in post processing, but need to work at before you start imaging.
The galaxy is green, i'm using Pixinsight with SCNR to remove the green cast so i'm not sure how to do it in other software.
The background could take some denoising, if you work with layers you can denoise only the background.

 

Slightly edited to remove greeen cast and reduce noise, just removing the green cast does a lot to reduce the noise btw!

 

[ollypenrice]

3 hours ago, vlaiv said:

 

@ollypenrice

What's with hue in that image / screenshot? Do you have some sort of color profile enabled in PS or something else? As far as I can tell - you opened above image to analyze histogram so it should be the same image, but to my eye and on my computer screen, two images are distinctly different in color - not sure if it will be seen by others as it might be issue with my computer, but here it is:

Left - your screen shot, right, original image. Maybe you did a bit of curves and levels and made hue different?

 

🤣 I knew it! I knew I shouldn't have posted that screen grab with you on the case!!!  I somehow managed to muck up my Ps profile settings when I opened it but rather than search for a solution then and there I pressed on with my reply to Alacant's post.  The evidence regarding the black point remained valid so I left it. Ignore the colour profile.

(Out of interest I don't know what I altered but a net search told me to close Ps then open it again while waiting a fraction of a second before hitting Shift/Control/Alt.  Well that might be easy for somoeone with the fingers of a concert pianist but it took me a good few attempts. Now fixed.

Olly

[Pompey Monkey]

On 23/02/2020 at 15:33, ollypenrice said:

🤣 I knew it! I knew I shouldn't have posted that screen grab with you on the case!!!  I somehow managed to muck up my Ps profile settings when I opened it but rather than search for a solution then and there I pressed on with my reply to Alacant's post.  The evidence regarding the black point remained valid so I left it. Ignore the colour profile.

(Out of interest I don't know what I altered but a net search told me to close Ps then open it again while waiting a fraction of a second before hitting Shift/Control/Alt.  Well that might be easy for somoeone with the fingers of a concert pianist but it took me a good few attempts. Now fixed.

Olly

Personally, I would never trust screen captures. Who knows what dithering/approximations/normalising etc. that your operating system does in a capture.

 

[Erling G-P]

You asked for comparisons, so here's my take on it.  Find it difficult for a beginner like myself and think I prefer your version, with the slightly greenish cast removed

SW 200 PDS, HEQ5  Pro, unguided, unmodded Nikon D7000, ISO 1600, 180 x 30 sec = 1½ hour, taken on 26-02-2019

[alacant]

13 hours ago, Erling G-P said:

180 x 30

Thanks. Excellent shot.

The 200 f5 helps bring it closer (we had only 200 f4). Nice idea with the lots of short frames rather then our (far fewer) but longer. You noise is also much better controlled than ours. Maybe the shorter exposures?

 

Edited February 25, 2020 by alacant

[ollypenrice]

19 hours ago, Pompey Monkey said:

Personally, I would never trust screen captures. Who knows what dithering/approximations/normalising etc. that your operating system does in a capture.

 

I experimented with this in a previous discussion with Alacant over the histogram and evidence of black clipping. I showed that a screen grab of his image (not this one) with its Levels histogram in Ps showed black clipping. But did this arise from the screen grab itself? I then took a screen grab of an image of my own, posted on here, opened it in Ps and looked at its histogram. There was no difference between the histogram of the screen grab and that of the original image. (I posted the evidence.) So for the purposes of looking at the histo related to black point I think the screen grab is roughly OK. It certainly won't work for all tests though.

Olly

[Pompey Monkey]

43 minutes ago, ollypenrice said:

I experimented with this in a previous discussion with Alacant over the histogram and evidence of black clipping. I showed that a screen grab of his image (not this one) with its Levels histogram in Ps showed black clipping. But did this arise from the screen grab itself? I then took a screen grab of an image of my own, posted on here, opened it in Ps and looked at its histogram. There was no difference between the histogram of the screen grab and that of the original image. (I posted the evidence.) So for the purposes of looking at the histo related to black point I think the screen grab is roughly OK. It certainly won't work for all tests though.

Olly

Useful to know

[Owmuchonomy]

Here is an old one of mine. Canon 600D standard and an Altair Astro ED 102 triplet.  Yours has way more detail I think but then I did pack imaging in because life was too short to spend processing. I never spent more than one hour processing any of my DSO images. I am not really qualified like others to offer sound advice.

 

[alacant]

11 hours ago, Owmuchonomy said:

. I never spent more than one hour processing any

Thanks for posting your version. I don't think it's lacking detail. We can see colour in yours where ours is lacking. Examples using similar resources help us enormously, hence our request when beginning the thread.

But yeah, I know. I'm lucky if my attention span extends much past 1/2 an hour.  I prefer to give the processing to a mate or two and let them argue over it!

But there is hope. New ways to process are evolving and will hopefully cut the screen staring to a minimum.

Cheers

 

Edited February 26, 2020 by alacant

[Erling G-P]

14 hours ago, alacant said:

Thanks. Excellent shot.

The 200 f5 helps bring it closer (we had only 200 f4). Nice idea with the lots of short frames rather then our (far fewer) but longer. You noise is also much better controlled than ours. Maybe the shorter exposures?

 

Thanks, however using many short subs wasn't so much a brilliant idea, but rather a necessity.  I really wanted to use longer subs, but going over 30 secs resulted in too many discarded ones.