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M13 with 6" RC - mono + DSLR


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With the last throws of astro darkness I decided to have a shot at M13.

I have already posted the mono version here but on Friday night it looked like the last chance to add colour so I attached the Canon M6 MkII to the RC and managed to get just 15x60s worth of colour at iso800, guided but not dithered.

The colour image was processed separately in PixInsight using the new NoiseXterminator process and the relatively new GeneralisedHyperbolicStretch plugin - just two moderate applications of the latter. I then applied CurvesTransformation too pull out a little more colour taking care not to over-saturate - I just wanted a trace of colour and not a Cecil B DeMille representation as is so often seen.

The mono and colour were then combined using LRGBCombination.

M13-Losc-GHS-x2-v2.thumb.png.7c8455e7c320043105c1c910430bbb09.png

Thanks for looking.

As always C&C are welcome.

Adrian

P.S. The M6 attached to the RC

IMG_3649.thumb.jpg.9c081a505a1f41b17886fbce29c19751.jpg

 

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Excellent M13, I do like your subtle approach to the saturation, good star resolution right to the core and the Propeller is clearly visible, as is the galaxy IC 4617,  at 11 o'clock. 👍

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2 minutes ago, tomato said:

Excellent M13, I do like your subtle approach to the saturation, good star resolution right to the core and the Propeller is clearly visible, as is the galaxy IC 4617,  at 11 o'clock. 👍

Thank you. I was surprised just how well the M6 performed considering it was only 15mins and there was a 97% Moon lighting up the heavens! I also captured 7x120s dithered but chose not to use them; I don't think it needs anymore but that a personal taste thing.

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Posted (edited)

Excellent m13. Saturation is realistic, in fact the image as a whole is realistic. I do see some color mottling in the background. This happens to me a lot.  There is an easy fix.  Extract a lightness layer, stretch it hard so that the stars get very bright but the background stays black ( I do mean black). Use as an inverted mask (protect stars) and use curves in saturation mode to crank down saturation ( a steep concave curve).  If one iteration is not enough, use 2.  This will not make the background darker. It will equalize the chroma and give a flat, background with respect to color. You will see that if you put the cursor on several points in the background, they will have the same r, g, b values. Those values will change from point to point, but they will be the same for all colors at each point.
 

ps…if you don’t use a strong mask to protect the stars and target— such as use an extracted lightness without manipulating it with curves, the curve adjustment you use will reduce saturation in the stars. They need to be fully protected

Edited by Rodd
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1 hour ago, Rodd said:

Excellent m13.

Thank you Rodd - I am pleased that you like it.

1 hour ago, Rodd said:

I do see some color mottling in the background. This happens to me a lot.  There is an easy fix.

Thanks for the tip - I'll give it a go later and see how I get on - your observations on the image and advice on fixes are much appreciated.

Adrian

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19 minutes ago, newbie alert said:

collimation looks spot on

Thank you.

defocus-rings.jpg.9bac35650ec31d9dbf8239bcce5fc622.jpg

This is a rather poor screenshot of the defocused stars - the rings are as close to concentric as I can get - I fear if I try any harder to get it perfect I will mess it up!

Adrian

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44 minutes ago, Adreneline said:

Thank you.

defocus-rings.jpg.9bac35650ec31d9dbf8239bcce5fc622.jpg

This is a rather poor screenshot of the defocused stars - the rings are as close to concentric as I can get - I fear if I try any harder to get it perfect I will mess it up!

Adrian

There's no need to touch it, looks spot on to me

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1 hour ago, teoria_del_big_bang said:

That's just brilliant, and I do think it looks better not glaring in blue.

I can't wait to get my RC6 up and running, plenty of time before we get astro darkness back.

Steve

Thank you Steve. You see too many images where colour seems to be everything - the more the better - but I think it often hides detail and structure and less is often more in the finished image.

The RC6 can be a challenge and it can be tempting to invest in all manner of expensive collimation devices - I have been tempted! In the end I just used a cheap laser eyepiece type thing to get it in the right ball park and then cast caution to stars and set about the secondary outside pointing at not too densely populated star field. I have to say I have taken it as a given that the primary was 'true' and upgraded the focuser to minimise droop. I've also used spacers to try to ensure there is minimal focuser extension. I think it has paid off. Non-astro dark is a perfect time to get these things sorted. Good luck!

Adrian

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1 minute ago, Adreneline said:

Thank you Steve. You see too many images where colour seems to be everything - the more the better - but I think it often hides detail and structure and less is often more in the finished image.

 

+1

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1 hour ago, FranckiM06 said:

Wow, it is fantastic image and very sharp. Also your process is very good. Congratulations about your wonderful image. I have done the same with my small diameter :( 

https://www.astrobin.com/h11pew/?active=2021

Thank you Francki for the kind comments. I've only been at this AP game for six years and I have always thought that imaging GCs is the hardest thing of all - which in part is why it's taken me six years to post one - my previous efforts have been dismal in all respects :( 

Hopefully I can get some more colour when the dark nights return and improve the signal to noise issue. I might also try my 6D instead of the M6 as the larger pixels would gather more signal and be better suited to the RC.

Adrian

P.S. Your M13 is definitely better than my effort - your background is much cleaner (no mottling) and there is every bit as much definition and colour in the core - if not more! Excellent job.

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On 15/05/2022 at 13:17, Rodd said:

I do see some color mottling in the background.

Hi Rodd.

I've taken on board your comments about background and had another go at the image. As ever I've introduced another variable, namely the addition of my 7 x 120s iso1600 subs.

855812776_M13-L175osc29-v2-x2.thumb.png.2ad015ceb1a04dbb52d3705fec2e3414.png

I hope you think the background has improved albeit at the expense of the stars - I probably should have left the 120s subs out.

I need to keep in mind this was never really intended to be an M13 imaging session - M13 was just convenient as part of the process of collimating my RC - a bonus so to speak.

It has certainly encouraged me to have a proper go at M13 once we get astro-darkness back in late July/early August.

Once again thank you for taking the time to give me your advice and feedback.

Adrian

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25 minutes ago, Adreneline said:

Hi Rodd.

I've taken on board your comments about background and had another go at the image. As ever I've introduced another variable, namely the addition of my 7 x 120s iso1600 subs.

855812776_M13-L175osc29-v2-x2.thumb.png.2ad015ceb1a04dbb52d3705fec2e3414.png

I hope you think the background has improved albeit at the expense of the stars - I probably should have left the 120s subs out.

I need to keep in mind this was never really intended to be an M13 imaging session - M13 was just convenient as part of the process of collimating my RC - a bonus so to speak.

It has certainly encouraged me to have a proper go at M13 once we get astro-darkness back in late July/early August.

Once again thank you for taking the time to give me your advice and feedback.

Adrian

The background looks great!  And the stars look good too. The image looks very real, like it would through a big dob.  I find Light pollution (or light from it not being astrodark can reek havoc with the background.  M13 is definitely worth a full effort. Globular clusters are amazing things that are not often given as much attention as other targets.  

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43 minutes ago, Rodd said:

The background looks great!  And the stars look good too. The image looks very real, like it would through a big dob.

Thank you Rodd. I've always steered away from GCs in the past because in my opinion they are the hardest things to image and image well. My previous attempts have been dismal for a whole variety of reasons.

I'm hooked now! I think my L data is all good, it's the osc/RGB data that needs more time. I might have a go with the 6D in the coming nights just to see how it performs alongside the M6 - the big pixels should help and as the detail is in the L the lower resolution should not be limiting.

Thank you again for your feedback and comments.

Adrian

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10 minutes ago, Adreneline said:

Thank you again for your feedback and comments.

One other suggestion.  If you are finding your star cores are a bit blown (doesn't take much), short subs work great to recapture core data (color mostly).  I tried imaging at high gain (300 with ASI 1600) and it tended to clip the stars (great for teh gtargets though).  But I made sure to collect 50 or so 10 sec subs for each channel and when integrated with the longer subs (either using HDR integration if you have PI, or just throwing them into the integration (or make 2 stacks and combine them after)--all the ways work.  Its a grat way to recover RGB stars.  Narrowband doesn't mater as much.

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