Finally, after about four months of un-useable weather here in the Northeast US, I had a single night with a few hours before the moon came up. Winter skies are just not much fun, nor is aligning and focusing in the cold, but worth it to make the most of the very few opportunities I get here to try anything. This is the first production use of my new Altair 26C (the IMX571 chip), and I can already see how much better the dynamic range is on the 16-bit sensor and how sensitive this CMOS chip is. Now I see why everybody has has so much success with the ZWO and QHY versions this past year. Hopefully it will keep paying off for me as the weather improves this spring.

I also managed a few frames with a new L-extreme filter, which I have also seen lots of great work with from others. Again, this has been in a box for several months. The contrast is great (I have to use a 6 minute frame length just to get the signal up away from the read noise), though I do see some star halos on Alnitak and a couple of the brighter stars. A little searching suggests that this is a pretty common issue with this and some other narrowband filters. In this case, I am able to blend the data in with the L-Pro integration, so it didn't matter too much.

I've verified (as suspected) that snow covering the ground reflects a lot of the already bad light pollution I deal with - my SQM meter registers about a 3/4 magnitude poorer from what I tend to get in the summer.

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Here's my post-processing list for anybody who's interested. I'm still figuring out the whole post-processing skill set, but I think I got a reasonable image for the limited data:

1. Image stacked in APP. The Dark library had a small issue on one edge from light leakage around the filter tray, but I heavily cropped the edges off anyway, so not a problem. L-Pro and L-extreme sets were stacked independently.

2. Background gradient removal was done in APP on both images.

3. I performed a rough initial stretch of both images in APP. The L-Extreme has some halo-ing around a few of the bright stars, but it also shows significantly more nebula content.

4. The stretched images were imported into GIMP as layers. I performed layer masking on the L-Extreme to isolated the red curtain zone and remove the halo stars. This layer was then set to 45% transparency and flattened again the L-pro one.

5. Next, PI was used for noise reduction -

(a) first, MultiScaleLinearTransform removed most of the noise;

some color artifacts were left.

(b) second, SNCR was used twice (green & blue) to remove most of the artifact from the red curtain.

(c) third, TGVDenoise was used three successive times to flatten out the residual artifacts;

this seems to work really well for this purpose.

(d) CurveTransformation used to stretch and balance the image again.

6. Finally, GIMP was used to enhance brightness, add in a little bit of Yellow hue to balance the coloring out slightly better, and one final small curve stretch.