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LBN683 and lots of galaxies in Ursa Major (mostly)


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With apologies to anyone who sees this on Astrobin, I mostly repeat the text from there....  

With some clear nights forecast in late February, I thought I'd try for a large mosaic of eight panels covering this huge area of IFN, categorised by Beverley Turner Lynds as LBN683. This seemed like a good use of the RASA with the milky way out of reach in the early hours, but I was perhaps fortunate to get all of the panels completed over 4 consecutive nights (unusual in Wales!). By some margin my biggest mosaic attempt.

As a bonus, you get M81 and M82, and various other galaxies dotted around - including 18 in the NGC catalogue and 5 ICs. These are obviously quite small in a field that's getting on for 6 x 8 degrees. I processed starless, and tried not to overcook the galaxies too much, but they are quite bright, despite taking on some hints kindly provided by @mackiedlm.  But perhaps that's OK in a large panorama, I don't know. Anyway, I need more practice at using GAME and other masking techniques I guess, but this is my end result for now at least.

I've been having trouble with my calibration recently, particularly the introduction of some fairly extreme colour gradients, exacerbated by vignetting. The mosaic makes these issues more obvious. This led to a lot of work with DBE, and still the need after that to reduce saturation on the main part of the image, while boosting it in the larger galaxies.  I know OSC images can be difficult to calibrate, but this is broadband, and I suspect I can improve mine with some experimentation - e.g. different length flats for RGB, my R signal is much weaker in the flats than the green.

RASA 11 v2 on CEM120, ASI2400MC Pro. Total of 1,093 x 30s (just over 9 hours), taken on 24th-27th Feb.

LBN683 230314 stretch.jpg

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