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M51 - The Whirlpool Galaxy - HaRGB - WIP


Gina

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SW MN190 (1000mm f5) on EQ8

OAG + LodeStar X2 + PHD 1.4

Atik 460EX Mono CCD

Baader RGB and Astrodon 5nm Ha filters

Artemis Capture, DSS, RegiStar, Photoshop CS5

Seeing was poor so all subs binned 2x2

Ha 6x20m + 3x10m

R 6x10m

G 6x10m

B 4x10m

Needs a lot more data hence work in progress.

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Seeing aroung here is rarely better that 2 seconds of arc from my observations but there are times when it's better.  With my scope and camera I get a resolution just under 1" per pixel.  That corresponds to an FWHM value of around 2 in average conditions.  Recently the sky has been somewhat below par and I have been getting FWHM values of 3 or more unbinned.  Hence my using 2x2 binning as mentioned above.  I have sometimes had much better seeing and I can sometimes use unbinned subs.  "Seeing" is defined as how the atmostphere randomly bends the light and produces wobbles in the image.  When long exposures are used this wobbling blurs the image.  Other problems are caused by water vapour (mist) and light pollution and should not be confused with "seeing".

I don't know why my image has come out so blue, I can only think that I have accentuated the lighter blue values over the darker ones when I have applied curves.  This may be as a result of having fewer blue subs than red or green - the blue needing more stretching - but I got the correction a bit wrong.  My best course of action would be to reprocess my RGB stacks, I think.

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I just thought it a bit odd that with not as much blue data as the red and green, that it's turned out blue. I would have thought it would have swayed towards the red or green? I'm certainly not saying it should be any other colour, just curious if there was a reason for it. Are you planning on any luminance or are you sticking to the ha as luminance?

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There's a sign that the seeing might improve once the current rainy spell has gone over and if so I may take unbinned luminance subs to add to my data.  Currently the Ha is added to red (about 30% lightening) and blue (7.5% lightening) representing the colour effect of hydrogen ionisation.

I have made a correction to the blue curve and compensated the other colours - here's the result.

post-13131-0-80346700-1427151174_thumb.p

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Set up tonight to gather luminance subs, unbinned, better seeing tonight - FWHM of around 2.4 unbinned.  Been out for the evening and only been going about half an hour so far.  Capturing 10m L subs unbinned.  The brightest part is just saturating in the very centre bit of M51B.

Here is a screenshot via TeamViewer.

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And first sub quickly processed with FITS Liberator and Photoshop then cropped and saved in PNG format for upload here.  This is pixel for pixel unbinned at full resolution - not resized.

post-13131-0-81172600-1427243996_thumb.p

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I am now so unbelievably anxious to order that 460exm.  Really coming together nicely.  Smooth guide graph too.  Also interesting to see the Artemis Capture. I like these posts showing the work in process. Good for us beginners to see more then just a finished product. "More More More," chants the crowd. 

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Thank you both :)  Glad my presentation is helpful Jeff G - very nice toknow :)

Here is a first go at the data from last night.  25 x 10m Lum subs unbinned, stacked in DSS and processed in Photoshop.  Cropped and resized to 1200px wide and saved in PNG format for upload here.  I'm not entirely happy with this as there are star haloes showing. A bit over cooked I think.  It may need separate processing for the faint nebulosity surrounding the galaxy from the stars and central part, then combined using layers.  There seems to be too much dynamic range for single image processing with the limitations of a PC monitor.

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The halo is smoothing out really nicely. I wouldn't worry about the saturated core. You could take your RGB core, discard the colour and use that to tame the real Lum core.

I do think that some part of the processing is hurting your stars - or is it just a JPEG artefact on here? I exclude stars from pretty well every aspect of processing and try to leave them alone.

Olly

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Thank you Olly :)  As I said, I thought this needed layers :)  There aren't any JPEG artefacts as this image is in PNG format.  No it's my processing :grin:

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Must bone up on the use of masking with layers :D

Heretic speaking so be warned; I very rarely use masks. I think there are simpler and better ways. To restore really nice field stars to your image I'd start with a linear Lum and stretch it like this...

CORE%20CONTROL%20CURVE-M.jpg

This curve climbs steeply at first to lift the background sky but flattens early to keep down the stars. (This is RGB but ignore that.)

Once you have exactly (you're an engineer so you know what exactly means  :grin: ) the same background sky value as in your main Lum you can just use Layers and the eraser to put your new field stars onto your hard-stretched main image. You might even find that the background sky was less noisy as well and could use that for the field. Layers, eraser, dead easy...

Like I said, I'm a heretic!!

Olly

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I've beeen using that method of holding the bright parts while lifting the halo but being mono, the opposite way round in Photoshop's curves.  This is what I get.  Cropped and resized and saved in PNG format.

post-13131-0-87492800-1427312313_thumb.p

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Thats coming along nicely Gina.

It might be worth looking into Russell Cromans StarShrink.

http://www.rc-astro.com/resources/StarShrink/

I've started to play with it and it works very well.

Or Straton, which lifts the stars out to allow more aggressive processing.

Of course, a star mask in PS will do similar, especially on an image like this where there isn't a lot of nebulosity.

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Thank you both :)  I'll look into star reduction software :)

I've done a reprocess starting with the red, blue, green, luminance and Ha stacks, aligned in RegiStar and combined in Photoshop.  Luminance used as Luminosity, RGB combined in Channels and Ha added as a Mode Lighten layer with Channels adjusted to Blue = 25% Red (approx) and Green set to zero.  Then the RGB set stretched a bit in curves before flattening the image.  Gradient Xterminator used together with various Noel's Actions and a small amount of sharpening.  Image cropped to about 1200 x 1024 pixels and saved in PNG format for upload.

post-13131-0-42873700-1427324383_thumb.p

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Thats coming along nicely Gina.

It might be worth looking into Russell Cromans StarShrink.

http://www.rc-astro.com/resources/StarShrink/

I've started to play with it and it works very well.

Or Straton, which lifts the stars out to allow more aggressive processing.

Of course, a star mask in PS will do similar, especially on an image like this where there isn't a lot of nebulosity.

Or Noel's Make Stars Smaller. I can often get away with two iterations of that one. However, there's a lot to be said for not stretching them in the first place on images where this is easy, like galaxies in starfields.

Olly

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Well...  I've scanned the forums, tried searching etc.  I know the info for using star masks in Photoshop is around and I've used it in the past but I can't remember how and now I can't find the info/tutorial.  Could someone point me to it, please?  :)

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