NGC5189 in Ha

[Lee]

After Rays sterling effort on the Bug, and Mikes on this one, I had to have a try.... :)
Normally I would have just dialled in really long subs for Ha, but thought I'd give shorter ones a go after Ray's advice - he was right, at 2min subs the SNR is pretty low....
I'm fairly happy with how this one turned out nonetheless.

52x2min subs, Astronomik 12nm Ha, Atik 420 and Bintel 200mm f/4 newt
Was done under a very high waxing gibbous moon.

The first image is just an average combine of the subs, with no dark subtraction at all (I realised at midnight I had no 1x1 2min darks!). I slapped it together in 10 minutes before going to bed. I've included it because I think the nebula itself looks the best in this image, if you ignore the trailing hot pixels....:whistle:

I found dark subtraction adversely affected the detail a fair bit, so I used a bad pixel map, and sigma clip stacking in Nebulosity for the second image, then processed again in StarTools. I had to stretch the data to within an inch of its life!

Hopefully I'll get some L and O-III subs when the moon goes....

[h0ughy]

not too bad - looks a lot like a symbol - &

stacking looks an interesting task- if you were to just park it on a star and let it go do you have any drift after 2 min?

[Shiraz]

that's a very interesting hi res result Lee - good backbone and really looking forward to the final image.

A few comments:
- Mike uses dithering with median stacking and I have used hot pixel removal with dark subtraction with the Sony chips. Interesting that you found that dark subtraction reduced detail - maybe I should do some rethinking.
- It sure is fun to process data from NB short subs with very low read/thermal noise chips, since there appears to be nothing much there. But when you really stretch it you realise that there is also nearly no noise, so you do eventually get a result :).
- your tracking looks really good at 2 minutes - maybe worth trying longer subs and see how much the atmosphere messes with the resolution? Modelling suggests about 5+ minute subs would be suitable with your system on brightish Ha targets, from a purely SNR point of view - but there may still be resolution advantages in keeping to shorter subs and your differential flexure might just start to distort stars at about 5 minutes I guess.

looking forward to the next installment. regards ray

[multiweb]

That looks very sharp. Well done. You can get rid of hot pixels easily with a bad pixel map made from one dark sub prior to register the light subs.

[Lee]

Not after 2 minutes, but plenty after 2 hours... sort of an auto-dither!

[Lee]

Thanks Ray...
I switched dithering off recently as I was having some issues, at present my polar drift is dithering as it is.... can't really do longer than 2min I think until I fix my PA.
It might just be me, but I could only get worse results if I dark subtracted the lights before stacking.
I did some 4 min subs on Sunday night, pretty ordinary really, mix of oblong stars and blurry (but brighter!) nebula....




Thanks Marc... I ended up doing that, have to tweak the BPM settings though, as some oversubtraction was occurring, so I had dark streaks instead of light, so I median combined them to remove...