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M13--Question


Rodd

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This is a question about globular clusters in general, M13 just happens to be an example I have to use for visual comparison.  I have spent a lot of time trying to perfect this image and keep coming back to this quandary.  The first image is M13 with a large profile--the outer stars are bright and there are not that many dim stars that one usually sees in the nether regions of globular clusters.  the second image is from the same data--just processed differently.  the cluster profile is smaller as far as bright stars go--and many of the outer stars are dimmer, gradually fading as one travels away from the center.   The core of the cluster is the same in both images.

Question:  Which is more correct?  My gut tells me the smaller profile cluster is more accurate.  As aperture and integration time increases, the cluster profile will increase until one has the Hubble image that encompasses the entire FOV.  My goal was to bring out as much of the cluster as possible, but I fear that my selective stretching and brightening has left the first image looking artificial.  I suppose the issue is are the stars in the far reaches of globular clusters smaller (younger), hence dimmer, or simply less populous, so the star field appears dimmer.  Is the core brighter simply because of star density?  or are the stars inherently more luminous.?

Please let me know what you think....am I on the right track in thinking #2 is more correct?  Or is it truly a matter of preference?  In that case--which is more preferable.  I have been switching back and forth between the two on my Astrobin page--but once printed, I am stuck, so I want to see what others think. 

Please ignore the very bright stars with the artifacts...I know they are distracting but they are, after all, not the center[piece of this image.  besides, they are the same in both.

Thanks in advance---Rodd

Large profile

1790638153_M13large.thumb.jpg.cacc83fdd597dda46728a478bf57f1b9.jpg

Smaller profile

M13small.thumb.jpg.4c5b09910f6af2099a5f8eaecbe3225e.jpg

Edited by Rodd
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7 minutes ago, Rob Sellent said:

I think they're both cracking images :thumbright:. However, purely from my own personal non-imager aesthetic, I prefer the second image :smiley:

Thanks Rob---yay...I am not crazy after all!

Rodd

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6 minutes ago, alan potts said:

I think you worry too much, both are superb shots, I just prefer the second image but anyone would be pleased with either.

Alan

AHHH--but the  little things make a difference.  After all...that tiny grain of sand in your shoe can sure seem like a boulder by the end of a long hike.  But I hear what you are saying.  If I had more clear sky time I would spend less time reworking and worrying about my images.  I would give almost anything for a good stretch of clear stable sky.

Rodd

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Hm, tough one ...

In second image I like the way cluster is rendered / presented - it is not too "in ones face" - outer regions are more subtle which I like.

There are however some things I prefer in first image. One is color tone, I find it more natural in first image - blue stars are as they ought to be and there are yellow stars. Second image has certain red tone shift to it as far as I can tell. Also in the first image, star shapes are better, or more natural looking - they appear to be too flat in second image for some reason. I'll post comparison to explain it better:

First image:

image.png.537911d5b94f57dcae952a636017c44c.png

In this section, you can tell that arrow is pointing to two stars, although they are "touching". Same region in second image:

image.png.6cc09dda2434eb7a407b59ec9f043f66.png

You can almost tell in this one too, but star edges are too abrupt - it almost looks like single elongated entity because there is some "glow" or "softness" missing around stars (background on the other hand,  to me looks better in second image).

Here is another example of two groups of stars that look better resolved in first image:

image.png.c12e42de17a131ac629d100188ba4424.png

Somewhat "flatter" look in second image (also, notice red cast in what should be yellow stars):

image.png.44bcdceea50896dfa66fafb8b0862fa8.png

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Firstly - two cracking images but with subtle differences.

Personally i would blend the core of the second image with image one and get rid of the slight red cast. Then stand back and be proud!

Well done.

If it makes you feel any better we got something resembling nearly dark back 2 weeks ago (56 North) so I assembled the rig in the obsy and since then we have had wall to wall cloud, biblical rain and 50kt winds !  Total sub count this season = zero! Opportunities to check polar alignment = zero !!

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8 minutes ago, vlaiv said:

There are however some things I prefer in first image.

Wow.....we have found it, ladies gentleman--the Six Million Dollar Man's bionic eye!  Pretty subtle Vlad......But i suppose I see your point.  However--these elements will not be visible in wall print (not that I am likely to spend the money to make one)....but that is the goal.  But, as I am fond of saying, the devil is in the details, so thank you for pointing out  some quantum ones.  I do not think I can "correct" the second image to match the details you pointed out in the first--maybe with some crafty Pixel Math replacement...we'll see.  maybe a simple 70-30 blend will accomplish it.  I could create a star mask for morphological transformation (a ring around each star) and replace the outer fuzzy area only--but that won't work in the cluster itself--the signal is too high.  the center 2/3 of the cluster will be black in the star mask......but its work a try for the outer regions.

Rodd

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19 minutes ago, vlaiv said:

Second image has certain red tone shift to it as far as I can tell.

 

9 minutes ago, Skipper Billy said:

get rid of the slight red cast

I do not see a red cast on my monitors.....But that is an easy fix anyway.  The real question is the outer stars--I gather from the posts that the majority "like" a fading profile from bright in center to dimmer at edges as opposed to one round equally bright ball.   That makes sense.

Rodd

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1 hour ago, Rodd said:

AHHH--but the  little things make a difference.  After all...that tiny grain of sand in your shoe can sure seem like a boulder by the end of a long hike.  But I hear what you are saying.  If I had more clear sky time I would spend less time reworking and worrying about my images.  I would give almost anything for a good stretch of clear stable sky.

Rodd

We lost most of May and June but at the moment we are about 16 nights on the bounce, we will pay for this.

Alan

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Both excellent images.

The second image looks more even and natural for me.

The first image has a slight darkness in the background at the edges of the cluster that for me, makes it look more unnatural than the second.

John

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10 minutes ago, Starwiz said:

The second image looks more even and natural for me.

Thanks John.  Yeah--the background kept getting away from me--the black point.  the problem is my sky is not very good, which results in a mottled, speckled background.  It doesn't look too bad at normal viewing, but at full resolution its terrible.  i have learned to control it by less aggressive stretches combined with selective black point reduction.....went too far.

Rodd

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22 minutes ago, astro mick said:

Rodd.

I don't know how you sleep at night,so many worries.

I just see this image for what is it,and that's exerllent.

Mick. 

Thanks Mick......sleep?   I have heard of it!

Rodd

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7 hours ago, MilwaukeeLion said:

Nice Cluster, taken some in lightroom for quick looks.  Clarity, no clarity, clarity, no clarity.  Similar to effect you show (wide and crisp vs compact with inner glow).   Kind of like inner glow myself.

I was trying to emulate the Hubble image.  There is no glow in the Hubble image, just stars. I like how the stars are resolved to the core....like Hubble.  But maybe I should increase the brightness in the core

Rodd

 

edit I did add some glow to the core. It’s the final image on my astrobin page.  I think it’s better. I don’t have access to the image now so I can’t post it

Rodd

Edited by Rodd
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4 hours ago, smr said:

I prefer the first one, I don't really know why, maybe looks like it has more depth in the cluster.

I like that aspect of it too. But I think that the natural profile of a globular cluster is a fading of stars with increased distance from the core. It makes sense in that the star field out there is not nearly as dense and the longer one collects photons, the more outlying dim stars will be picked up. The first image doesn’t really have an outer periphery, it just falls right off.   That is because I selectively stretched the outer part of the cluster wanting to mimic long exposure depth. That’s what I get for cheating!🤕

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