The Fish Nebula (Don Walters)

Celestial hemisphere: Northern · Constellation: Cassiopeia (Cas) · Contains: IC 1795 · NGC 896

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The Fish Nebula

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The Fish Nebula

My second narrowband target. The stars look much better, and overall I'm much happier with this than I was with the Pacman Nebula.

The big difference this time was I started using very high gain on my camera (Gain 270 / Offset 340) and shooting much shorter exposures (just 90 seconds). This has turned out to be a wonderful plan! By using such short exposures, I'm able to get much better guiding, and throwing away bad exposures is not such a big sacrifice when you're scrapping only 90 second subs.

I also noticed that OIII usually renders poor stacks. Experts on Cloudy Nights have told me that OIII is "much closer to the noise floor" so that's why its so noisy compared to Ha. To help remedy this, I shot a WHOLE LOT more exposures in OIII trying to squash it. It helped, but not as much as I'd hoped. I think this is going to be my plan from now on.

One thing I noticed is there are a lot of cold pixels when zooming in close. I tried using PixInsight's Cosmetic Correction tool, which is supposed to remove these, but I couldn't seem to make it work. The tool is supposed to be used on the individual frames before stacking, but when I tried, I found that those frames were like static; there was a grainy appearance in the frames which made spotting the cold pixels almost impossible. Only after stacking was I able to find them. And combining the channels to generate the color image really enhanced them. By then, it was too late to use the tool. I really need to learn more about using this tool.

Colors were blended a follows:

Red: HA

Green: 20% Ha / 80% OIII

Blue: OIII

If I favored the Ha, the result was more orange than red. Only by shifting to the OIII was I able to get more red.

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The “AstroBin Image of the Day and Top Picks”, or IOTD/TP, is a long-running system to promote beautiful, interesting, peculiar, or otherwise amazing astrophotographs, with a focus on technical excellence. Learn more.

Submitted The date and time when you submitted this image for IOTD/TP consideration.	...
Views by Submitters (available since September 19th, 2023) Every image is assigned to 50% of available Submitters. In the event that at least 80% of them don't view the image before its time in the IOTD/TP process expires, it's assigned to the other 50% of Submitters and the process begins anew.
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Status	Basic success
Started	...
Astrometry.net job	1342297
PixInsight job	n/a
PixInsight queue size	n/a
PixInsight stage	n/a

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