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 Post subject: The Pleiades
PostPosted: Sat Sep 22, 2012 2:13 pm 
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Hi folks,

The Pleiades were the subject I chose for "first light" when I got my imaging system up and running earlier in the year. I promised myself I would return to them in the autumn and here's the result, uncropped apart from a 48 pixel wide border but then downsized by a factor of four:

    Image

      The Pleiades

I've linked to a larger (2048 x 2048 pixel) version which you can see by clicking the image. The 4096 x 4096 pixel original doesn't really add anything to the party in terms of extra resolution of the nebulosity. The subs used were 5 x 1,000 seconds blue and 5 x 200 seconds in each of red, green and blue using my Astrodon Tru-Image filters. As ever the 'scope was my TEC 140 and the camera an ML16803.

Processing was a real challenge for me because the brightest stars were still well blown even on the 200 second subs. In the end I decided to do without any shorter exposures so I combined the 200 second RGB subs to get a colour image and combined the 200 and 1000 second blue subs using PI's HDRComposition tool to get a much deeper image of the reflection nebulosity while still controlling the size of the brightest stars. That image then had its stars removed and that's where the fun started as there was no way I could reliably clone out the brightest stars as they were so intimately bound with the illumination of the surrounding gas and dust. In the end I opted just to darken the very brightest stars as the whole purpose of the exercise was to try and prevent ringing during subsequent processing of the nebulosity and ringing is basically triggered by very sharp transitions in brightness. Anyway, the "no stars" image went back from Photoshop into PI where the tool of choice was LocalHistogramEqualisation. The original plus the LHE version were both processed further in Photoshop and then blended together and the result coloured using a Curves layer. The cleaned up and enhanced RGB image was then added as a screen layer which neatly added the stars back, including over-painting those problematic very bright ones, and also slightly modified the colours of part of the brightest areas of the nebulosity. Obviously there were lots of extra tweaks along the way but those were the headline steps.

Quite an adventure and there's always a worry that the end result owes too much to the choices during post rather than reflecting (sic) what was actually there but I'm pleased with the result, especially as I wasn't expecting to see so much structure so distant from the Pleiades themselves. I hope you like the result.

Bob.

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 Post subject: Re: The Pleiades
PostPosted: Sat Sep 22, 2012 10:25 pm 
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This has to be one of the deepest images I've seen of it. The work processing it paid off! This is on my "to revisit" list and I'll be happy if I even get half as far...

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 Post subject: Re: The Pleiades
PostPosted: Sun Sep 23, 2012 9:06 am 
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Hi popo,

Thanks for that. This image has surprised me in a few ways. Firstly, the amount of structure that can be extracted from the brighter areas and secondly the extent of the fainter region. Of course, once you know it's there it is possible to find other images (e.g. this APOD from five years ago) but the vast bulk of images revealed by Googling give little hint that so much is going on. But the biggest surprise is the muted response over at Stargazer's and I'm forced to ask myself why? Have I overdone the processing in order to reveal the bright structure or was my colour choice for the faint bits a little off? Coincidentally, that choice isn't so far away from the APOD palette, which I hadn't seen until after my first draft was complete, so I'm a little doubtful it's the colour choice that is at fault. :?

I'm tempted to ask just why so few images out in the wild show the surrounding nebulosity. OK, I do use a large cooled CCD and yes, I was scratching around just above the noise floor of my data but heck, that was only 5 x 1,000 seconds (comfortably less than an hour and a half) of imaging through the blue filter and that at a comparatively dim f/7. :shock:

What's going on? Don't folk believe the data they see on their images or don't they want to show what's actually there? I'll ask that question at Stargazer's in about a week's time in a gentler fashion once I get, or don't get, a few more comments.

Bob.

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 Post subject: Re: The Pleiades
PostPosted: Sun Sep 23, 2012 9:26 am 
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One thing I found out a long time ago is not to put too much into what other people like. Certainly for my wildlife photos I post on deviantart, what I think are great shots may get relatively little interest, whereas a so-so shot might go off the scale. There may be something there about subject popularity, but I gave up trying to understand what's hot or not out there.

On this specific subject though, I've not really paid much attention to depth previously although I'm tempted to hunt out a Greg attempt for comparison. I'm having a severe maths fail at the moment to work out how slow f/7 is relative to my setup, not considering imager sensitivities, but as a vague ball park value I think I can easily get similar exposure depths. I will for sure have a go at this myself in the not too distant future, subject to local light pollution limits anyway... it needs to move further away from a local shopping centre before I have a serious go at it.

BTW Bob, if it's not getting too late in the season I'd be really interested to see how deep you could go on the Veil...

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 Post subject: Re: The Pleiades
PostPosted: Sun Sep 23, 2012 10:10 am 
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Hi popo,

I'll leave Greg to offer something should he happen across this thread. He does mention the extended nebulosity in his very useful book "Making Beautiful Deep-Sky Images" but I don't think the printing process was as kind as it should have been.

As for the Veil, it is definitely on my TODO list and it is well placed just beyond the meridian next month. That said I do find that my mount doesn't track the long exposures quite so well on that side of the meridian (I'll have to re-train it at some point) so 1,000 second exposures might be pushing the limit. I think my best plan is to concentrate on the plentiful array of targets now coming into view in the east and leave the Veil until next year at which point I'll have those extra narrowband filters. The entire complex would be an easy target for my Pentax 165mm f/2.8 but I think I'd rather try for a two panel mosaic with the TEC 140. Might be slightly cropped north/south if TheSkyX is to be believed but I'll comfortably see both the eastern and western extremities with such a mosaic.

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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 Post subject: Re: The Pleiades
PostPosted: Sun Sep 23, 2012 11:06 am 
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The Veil does cross the meridian when doing evening imaging at the moment, but I just skip the flip and keep going as long as I can before guidecam meets tripod leg. I know your mount is intended to be usable unguided, but is adding guiding be a "quick fix" option for longer exposures? And it certainly is bigger than the most visible east/west parts. I've missed the lowest parts with my current framing... I should have checked that before I started... instead of more or less centralising the bright parts.

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 Post subject: Re: The Pleiades
PostPosted: Mon Oct 01, 2012 10:44 am 
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popo wrote:
One thing I found out a long time ago is not to put too much into what other people like...

While I was away last week the Stargazer's thread for the image above kicked off in a major way. Funny how an image can go unnoticed initially but very gratifying to receive such nice comments as well as an occasional bit of useful feedback. 8)

Of course taking your quote above in its new context I should start to get worried! :twisted:

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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 Post subject: Re: The Pleiades
PostPosted: Mon Oct 01, 2012 11:28 am 
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First off - it is an excellent image of the M45 region Bob - well done! There are a few images out there that go as deep (not many!) and some with a much larger field of view so that you can actually see how the two vast regions of reflection nebulosity surround the Pleiades and fill the whole region.

My deepest image of the region is here, this is one of the two M45 images in Star Vistas:

Image
M45_Wide_Deep_Field_Greg_Noel_small by cybermystic, on Flickr

This is made up from goodness knows what subs, but includes Sky 90 + M25C data with subs that I think went up to 15-minutes. I think you will have captured more of the surrounding dust due to a more sensitive camera (in the blue?) and possibly your skyglow conditions are better than mine - dunno. I would be interested to see if you can see anything of the supernova remnant CTB1 on the edge of Cassiopeia - I am pretty sure it's beyond my capabilities here due to my skyglow.

Greg

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 Post subject: Re: The Pleiades
PostPosted: Mon Oct 01, 2012 11:31 am 
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P.S. I seem to have picked up a lot more of the very faint extended red emission (ERE) around Merope than you, but this might just be down to you using shorter red subs compared to the blue.
Greg

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 Post subject: Re: The Pleiades
PostPosted: Mon Oct 01, 2012 11:49 am 
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Hi Greg,

That red emission is more obvious on my RGB image from the 200 second subs but when I added it to the 1,000 second blue data it got a little washed out, My processing skills still need work! Thanks for the kind words - they mean a lot when they come from an astrophotographer with your own track record. 8)

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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 Post subject: Re: The Pleiades
PostPosted: Tue Oct 02, 2012 8:05 am 
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Hi Bob,

I'm sure I don't need to tell you, but to create a "true colour" image (and thus see the ERE as it "should" appear) you need to take the subs according to the sensitivity of your camera to the R G and B. By highly overdoing the blue you will do what you wanted which was to bring out all the reflection nebulosity, but you will sacrifice all the subtle star colours you can see in the Parker/Carboni image. However - if it was just the reflection nebulosity you wanted - you couldn't have done a lot better :D

Greg

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 Post subject: Re: The Pleiades
PostPosted: Tue Oct 02, 2012 8:41 am 
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Hi Greg,

Good words. That idea informed my decision to add the RGB stars plus nebulosity to the deep blue image, which had had its stars removed, via a Screen layer in Photoshop. As a result the star colours were pretty much retained. The partial loss of the red emission signal was due to the signal level from the deep blue nebulosity being similar to that of the nebulosity in the same region of the RGB image. I might experiment with adding a "no stars" RGB image as a Photoshop Colour layer to the deep blue nebulosity although I have a feeling things won't be that simple and I might have to end up selectively masking to get the colour I want in the relevant areas. All part of the learning curve but good practice as similar problems will no doubt arrive when combining RGB of, say, the Flame Nebula with a deep Hα image.

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
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 Post subject: Re: The Pleiades
PostPosted: Sat Oct 20, 2012 11:01 am 
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Hi folks,

I've reworked my image of the Pleiades with this result:

    Image

      The Pleiades - M45

I've tried to tease a little more out of my limited data set and emphasise the red nebulosity near Merope. The image is clickable for a 2048x2048 pixel version.

The difference is subtle by design as I knocked back the opacity of the new PhotoShop "Screen" layer to under 50% but, I hope, still worthwhile. That said, I really am scratching perilously close to the background noise in my original 200 second Red subs so at some stage I really need to add 1,000 second subs in both red and green to the 1,000 second blue subs and reprocess right from the beginning. Whether the extra red data will be deep enough to show the redder areas near the periphery of the image is moot but with our limited access to clear skies here in the UK I think that project will have to be deferred as I have other targets in mind over the coming months. :)

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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 Post subject: Re: The Pleiades
PostPosted: Sat Dec 08, 2012 6:29 pm 
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Hi folks,

My knowledge of how to "stretch" the image so that the high dynamic range (think greater than 16 bits) can be squeezed down to an 8 bit JPEG has improved. As an aside, stretching to squeeze sounds like an oxymoron, come to think of it.

Anyway, as a result I've done a final rework of my Pleiades data. I won't be returning to this object again until I can gather some more subs, particularly the 1,000 second subs in red and green I need to better inform the colour of the extended nebulosity which should probably be more reddish/brown than blue. This time I've gone for a very different final look with the intent of preserving the jewel like appearance of the bright stars of the cluster, rather lost in my previous treatment, whilst also significantly enhancing the filamentary appearance of the nebulosity. Maybe that was a step too far but from typical viewing distances it gives the effect I want.

    Image

Hope you like it.

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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 Post subject: Re: The Pleiades
PostPosted: Sun Dec 09, 2012 2:25 pm 
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As always, I'm no expert whatsoever and I really don't know much about this, but I think this last one looks a lot better, I just like it more. Good job :)

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