StarTools

First imaging of the month last night, other than the goofy comet that is.

Only 2.5 hours LRGBHa, in moderately poor seeing. Will try to get more time before the month is out, which also should help if I try to crop in and bin less.

With such short time, things were pretty noisy. And in Bortle 8, unlikely to be IFN!

But after smashing and squeezing all that out of the way, the background still has a whole lot of surrounding little goodies. The three sizeable galaxies of course, and tons of tiny ones, but also a few small blobs like Holmberg IX, another two that are very similar, and M81 Dwarf B.

Color was set by star mask sampling and then left alone other than green cap (which was minimal). The stars seem pretty well in the ballpark of reported B-V values, but I have seen M81's with more blue. I wonder if I could use a little more bias here. And if it's off a bit, I suppose this region may not be a properly representative sample of stars?

Or maybe just this bin level isn't allowing the blue portions of M81's outer arms to stand out.

Mike,
Very good image considering limited data , poor seeing conditions and LP
I don’t know this Galaxy group but agree some blue is missing ?

Well done !!
Martin

Thanks Martin. Just a start though...

Good to get other eyes on it, I'll check references and see if it can rationally be fed more blue or maybe it needs red reduction, and watch the NB Accenting as well.

Yes I think this group is about +70°. Very popular up here. It was first light on both of my telescopes, and a lot of others seem to first light this target as well.

Looks really nice Mike, nice colors and they stand out well, despite the rather short integation time.

good job

Maybe this could be my next target ....

Hi Mike, nice! I like the fine Ha structures you captured in the cigar. And I like the FOV, containing all these small galaxies in the neighbourhood
I too would assume, that there's some blue missing ...

I'm not sure, if colour calibration with star sampling could be disturbed for whatever reason? Maybe something which lies in the data set ... stacking, RGB alignment, over saturated stars ... ?

I remember Stefan's excellent image of this galaxies two year ago and I think, the colouring looks quite reasonable ... ?
viewtopic.php?f=11&t=2539&hilit=m81

Best regards, Dietmar.

Thanks Dietmar.

Glad the consensus is that I am missing blue (or maybe strong in red, to the extent it's all relative of sorts in the Color bias?), I'll have to work on that for the next go-round.

RGB alignment should be pretty good? From what I've seen WBPP is a lot more precise on that, and I don't have to use highlight repair as often or as strongly as with, say, ASTAP, which makes you register the different filters afterwards.

I doubled up the integration last night, and will stack it all together shortly. Seeing was much better, at least for the first hour, but then it seems like some high hazy clouds started passing through at the end. Might impact the extra 30m of Ha.

Will just have to see if I can get some more fine detail and those extended tendrils of M82. Probably not.

Saturday night I had some clear sky, decent seeing, and only at the end during Ha subs did some high hazy clouds impact the acquisition. So, doubled up my integration and now have my seemingly standard 5 hours.

2h L, 40m ea RGB, 1h Ha. PI WBPP for stacking.

This, again, was binned 35% for the edit. I'll try both less binning and tighter crops later on.

Instead of star sampling I just ran a full mask sample when entering Color, and this gave a starting point already a bit more blue biased than when using stars. Still not a ton, I think red was reduced 1.08 and green 1.06, with blue left alone. I altered these just a little bit, red reducing to 1.15 and green to 1.08, then green capped, and I think the balance turned out better. Some decent blue is showing in the arms of Bode's, and the whatever of Cigar. A little bit of blue center shows fairly strongly in the core of Garland, which concerned me, but I believe actually matches up with the handful of reference images out there.

I used two Layer+Undo reversals here. First was after SVD, as I am unsure of the pinpointing of Bode's and Garland cores into stars. But, minimal change and the mask was only a handful of pixels.

The second Undo was after NB Accent, for the pinking of continuum light (even blue stars) as we've discussed before. I also added the main central disk of M81, which seems unusually prone to pinking. Maybe it's particularly bright, or something I did during HDR? Often that's handled through settings in NBA screen 2, as worked on my NGC 2403, but I couldn't make it work here.

The really interesting quandary for it though is M82. I can't think of any good way to differentiate real hydrogen from continuum Ha in that bright little cigar. Some references seem to show it staying pretty brown in that cylindrical "core," with the true hydrogen bursting out from the sides. But in my NB Accenting it all becomes pretty red and pink in there. I may have to try to work on my Screen 1 settings some more to see what transfers over, but I don't think there's much getting away from that continuum brightness.

The other night I ran a cropped edit of the data, and only binned 71. Some good and some bad...

I think the NB Accent worked better around M82 at this scaling. I also brought the bright saturation way down in Color, as I think it was darkening/reddening the core disk of M81 too much.

I also just left the M81 core as-is without reversing any little starization in SVD. I don't think it turned out too bad at this scale. Though I'm still not sure I'm entirely on board with the propriety of it. I didn't yet try out extended dynamic range - in the past that has seemed to darken the overall image a lot.

However, the scale also revealed just how bad my star shapes have become. They were all triangles! And no amount of spatial error in SVD would help. I guess I'll have to take the Newt apart. Maybe the mirror is binding on the supports, or possibly it's been cold enough - though I hadn't thought so - for metal contraction to cause pinched optics via the mirror cell or the clips? Sigh.

Granted this post has been downsampled yet again for size purposes, but some of the triangles still carried over. I think my final image will have to be the full FOV, binned/downsampled sufficiently to round off the triangles best I can.

Mike in Rancho wrote: ↑Fri Feb 24, 2023 9:03 am However, the scale also revealed just how bad my star shapes have become. They were all triangles! And no amount of spatial error in SVD would help. I guess I'll have to take the Newt apart. Maybe the mirror is binding on the supports, or possibly it's been cold enough - though I hadn't thought so - for metal contraction to cause pinched optics via the mirror cell or the clips?

Yes, Mike! I once had triangle shaped stars as well , after I took the main mirror apart for cleaning. I tightened the clips holding the mirror to much. Next try was to put a piece of thin paper between clip and mirror (only while assembling) and not to tighten these screws. Don't know, if this is the recommended way, but it helped.

Best regards, Dietmar.

decay wrote: ↑Fri Feb 24, 2023 4:34 pm
Yes, Mike! I once had triangle shaped stars as well , after I took the main mirror apart for cleaning. I tightened the clips holding the mirror to much. Next try was to put a piece of thin paper between clip and mirror (only while assembling) and not to tighten these screws. Don't know, if this is the recommended way, but it helped.

Best regards, Dietmar.

Thanks, Dietmar.

I thought I was pretty careful the last time I put it together, but I was also trying to prevent any mirror movement that could cause flats to miscalibrate. So I may have been right on the edge, and perhaps these lower temps pushed it into pinching. The rubber of the clips was just barely touching the mirror surface (really the beveled surround) without pressure.

The mirror wouldn't shift laterally, nor move upwards, but I could pretty easily rotate it by hand. But that was inside and probably 75°, so could be different at 45°!

I'll take it apart and give it a tiny bit more space.