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M33 Wide-ish...

ollypenrice

By ollypenrice
in Imaging - Deep Sky

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ollypenrice

ollypenrice

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Last night guest Julian and I pointed our respective Tak FSQ85s at M33, mine with our Atik 4000 aboard and Julian's with his new Atik460. We'll publish the shoot out ASAP.

This has last night's data of an hour per colour and 90 mins Lum but I then resized an older M33 2 panel mosaic from the TEC140 and blended that on top as well. Plenty of data, then!!

Out of interest the image follows my usual galaxy workflow of ending with a softly stretched RGB only layer for the background sky and stars. This keeps them small.

And here we go...

Olly

LRGB-Ha-TAK-TEC-X2.jpg

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ollypenrice

ollypenrice

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Very nice... How do you do a star-only RGB stretch?

Just take the linear RGB layer without luminance and stretch it by lifting the bottom of the curve steeply but then flattening it off far earlier than usual. You are trying to lift the background sky to the same values it has in your finished LRGB image while stretching the stars far less than before. Use the colour sampler in Ps to measure the background in both images and adjust the background in the RGB till it is exactly the same in all three channels as the LRGB.

Then paste the LRGB onto the soft RGB stretch and try an erasor set to 50% to wipe off the LRGB stars and background around the galaxy. You can see whether to erase the LRGB stars and background completely or partially to taste.

Olly

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ollypenrice

ollypenrice

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Thanks, I'll translate that to a one-shot DSLR and Gimp setup. I don't get enough data to get the galaxies looking good but I do get nice color on my stars which I lose when I stretch the image.

Ah yes, that's the lack of well depth. With a DSLR you'll soon burn star colour to white but this method will work fine for you. You do see good star colour in DSLR images when the imager knows how to retain it.

It also tends to reduce noise in the background sky.

Olly

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ollypenrice

ollypenrice

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Thanks for the kindness, folks. I grubbed around for Ha to add to the bit I captured on the night and found some older data. Julian also donated his from the original night so here's the final version. I'm not one for heavy Ha doses, though, so not much 'bling' effect (to quote Martin's memorable quip!)

Olly

M33-FIN-HamaxLRGB-nr2-X2.jpg

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AndyUK

AndyUK

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A beautiful image as always Olly!. I'll be very interested to see / hear the results on comparing the 4000 with the 460 - One day I'd like to see one of these in my case :rolleyes:. And that's a very neat trick for controlling the size of the RGB stars too - Thanks! :smiley:

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ollypenrice

ollypenrice

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A beautiful image as always Olly!. I'll be very interested to see / hear the results on comparing the 4000 with the 460 - One day I'd like to see one of these in my case :rolleyes:. And that's a very neat trick for controlling the size of the RGB stars too - Thanks! :smiley:

Thanks Andy. On images with lots of defined background sky (ie galaxies and PNs) the separate stretch works well. In the case of 7331 and the Quintet I put the deep stretch underneath, reduced the opacity of the upper background sky layer, and erased it wherever there was a faint fuzzy underneath, then raised the opacity of the top layer before flattening. (Just noticed this image is flipped. Sorry about that!)

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-Pm9g5nM/0/X3/stephans-quintet-X3.jpg

The 460/4000 comparison is now here; http://stargazerslounge.com/topic/162996-atik-460-versus-atik-4000-shootout/

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MartinB

MartinB

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Bang on the button again Olly. I confess I like those little rubies. Your star layer has worked a treat. I guess it works best for galaxies and targets without extended nebulosity. Dodgy stars are a real pain when there is processed nebulosity around.

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