First light ASI2600MC and ZWO filter wheel

[SkyHiker]

This is my first attempt at a narrowband image with the ASI2600MC and the 7 position 36 mm ZWO filter wheel. I recently presented a basic test in this thread, viewtopic.php?p=171976#p171976 . Target is the wizard, NGC 7380.

The data was taken last night: 8x5 min Halpha, 16x5 min OIII and 8x5 min SII. The OIII run had a few subs with clouds in it and it got worse from there on so the SII data was next to nothing - I don't think there is much of that anyway. So it's pretty much an H-alpha image with some shades of OIII in it but not much.

To stack this in DSS I selected the first H-alpha image as a reference frame. The lights are split into 3 groups, while the flats and biases are in the main group so they get used by all. I opted to use the luminosity filter for the flats and apply them to all light groups. Some people say this is not recommended but if it works it saves time.

I processed the stacked Autosave.tifs, one for each filter, in Gimp. Basically, stretch and filter the data in greyscale. Then apply Colors->Components->Compose... to combine the colors. I had read that the Hubble palette mapping is (Ha,O3,S2)->(G,B,R) but the result was all green so I opted for (R,B,G).

One detail is that while DSS says the images should be aligned, whan I imported them in Gimp there was an offset difference. This was easy to fix with the Layer->Transform->Offset... tool.

I added the sum of all edited components into a luminosity greyscale and copied that into another layer, then assigned it as a Luminescence from the Mode pulldown in the Layers dialog. This lit up the image quite a bit. It also introduced a lot of noise that I had to despeckle and denoise.

The result is so so because there was simply not enough OIII to add some color differentiation, and the OIII and SII signal was rather low so the edges looks abit coarse. And the red is redder than I like. I attached the luminosity image too because to me it's more pleasing than the color image. This is all just about the experience, I'm not a perfectionist right now. I'm not unhappy with the result, for a first time.

I should mention that the data acquisition was not difficult at all. Once you have it all set up the extra work is that you refocus before the next filter group, which is not much work and it's fun too with the EAF autofocuser. No need to get up from your seat.

One thing that is worrisome is the large stars to the lower left. There, I see soma-like fanning. I have noticed that the vanes that hold the secondary mirror tilt a bit when the scope moves to a different position, and the scope loses its collimation. Over a couple of hours there is a significant position change. If this is causing those stars, I'm not sure what I can do. At least I know where to look.