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A summer Pinwheel - M101 Galaxy (LHaRGB) June 2021


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15 minutes ago, geoflewis said:

Hi all,
It's been a slow year for imaging, with most of galaxy season a wash. We are now into 2+ months of no astro dark from my 52N location, but with a run of recent clear nights I thought I'd have a try at M101 in Ursa Major. This proved a very difficult target with the RGB data suffering badly from background sky gradients, I think mostly caused by the rapidly varying sky brightness over the barely 3 hours per night of limited darkness, as the sky rapidly moved from nautical twilight, through astro twilight and back to nautical twilight between 11:30pm and 2:30am. In fact to get the final result I had to discard a significant proportion of the RGB subs, including about 50% of the green data, as unusable, as they were producing a blotchy green and magenta background that was very difficult to process away.
I'm still not sure about the final colours, but anyway here is my look at a summer Pinwheel...


Thanks for looking.

It looks great considering the conditions you were shooting under. The Ha regions in the galaxy really stand out.

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  • 2 weeks later...

I keep coming back to this image as I don't like the overly magenta hue and the galaxy arms should be a fairly intense blue/cyan. Hence, I've reprocessed it applying selective colour adjustments to the 'blues' to give them more emphasis. Also additional curves and levels adjustments for more contrast and brightness in the galaxy to lift it from the background and ran a gentle high pass filter to enhance structures within the galaxy.


Thanks for looking and please be honest if you think this version is better or worse....

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2 hours ago, DaveS said:

Colours looks good, but I think the dust clouds in the arms look a bit "crunchy". Just my opinion of course.

Thanks David, I wondered about that too. I alternated between ramping up and dialling down the use of the high pass filter, ended up somewhere between the two....

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