February 27, 2021: First Foray into Multi-Colour Narrow-Band Imaging

[michael.h.f.wilkinson]

Yesterday was an unexpected clear(ish) night, so despite a full moon, occasional scudding hazy clouds, and later increasing haze and fog, I set up my latest wide-field imaging rig, consisting on my ASI183MM-Pro, combined with my Sigma 50-100 mm F/1.8 zoom, with a ZWO 5 position EFW, equipped with a Baader L filter, and three Baader F/2 narrow-band filters (H-alpha, O-III, and S-II), all on the old EQ3-2, tracked, not guided. I managed to get 30 120 s Subs in H-alpha and O-III, but only 9 in S-II, when fog scuppered any further attempts. I captured flats and dark flats in all three bands separately, and used a single master dark taken the day before (I just love set-point cooling, which is comparatively new to me). Using multi-channel stacking in APP processing the load automatically was really a breeze. Here are the individual channels after a little strecth in GIMP:

H-alpha

O-III

S-II

H-alpha is clearly best, with the best signal and least trouble with moonlight. O-III shows some nebulosity, much more starlight, and more problems with moonlight. S-II is worst, showing little signal (unsurprising with just 18 minutes of data and increasing fog). I did a quick combination of channels in GIMP, and HOO is not too bad:

But SHO is problematic due to the lack of meaningful S-II data:

Still, quite pleased with the results, as I learned that the performance of teh Sigma zoom at full aperture is very impressive. This is not unexpected given how it performed on NEOWISE last summer. The rig seems to work well, with my EFW being in action for the first time. The forecast for Monday and Tuesday night are pretty good, so fingers crossed I can get more data (especially S-II, and some O-III before moonrise)

 

 

[Laurin Dave]

That's a good result for your first time and for the integration time..  You can get rid of the green in Photoshop (and maybe GIMP... I'm just not familiar with it) with Selective Colour, tutorials online on how to do it or as I've done below in Pixinsight with scnr...

Dave

[michael.h.f.wilkinson]

31 minutes ago, Laurin Dave said:

That's a good result for your first time and for the integration time..  You can get rid of the green in Photoshop (and maybe GIMP... I'm just not familiar with it) with Selective Colour, tutorials online on how to do it or as I've done below in Pixinsight with scnr...

Dave

Cheers Dave, I think I will first get loads more data before experimenting with ways to combine the bands. There are many options in Gimp, Affinity Photo, and indeed APP itself to fiddle with the exact mixture, but I feel the S-II data are so bad you cannot really hope to mix them in meaningfully. Next time I will start grabbing O-III, before moonrise, then switch to a long session of S-II, and then, if time allows, also do extra H-alpha. 

[michael.h.f.wilkinson]

Couldn't resist fiddling with the HOO rendition, and using H-alpha as luminance channel I think I get a better result.

[CraigT82]

Very nice, just taking fist tentative steps into narrowband myself. What target is this?

[michael.h.f.wilkinson]

35 minutes ago, CraigT82 said:

Very nice, just taking fist tentative steps into narrowband myself. What target is this?

This is a wide-field image of the Flaming Star Nebula (IC 405) to the right, IC 410 and NGC 1893 beside it M38 is at the top with NGC 1907 below it. To the lower left we have M36, IC 417 and NGC 1931 are in the centre, and various Sharpless nebulae are top left (Sh2-231, 232, 233 and 235, I think). It's a crowded area