Soul Nebula (IC1848) and Great Orion Nebula (M42)

I never did take the 60Da/NP101/G11 down, so I had a great starting point for imaging last night. Since there was not a guide scope in that setup, and I don’t have a way to easily add one, either my tracking was going to be good enough to image and I could proceed, or the session would have ended before it got started. While I was taking test shots to get my exposure right I found that 20s at ISO 800 was my sweet spot, and my stars appeared round. I concluded that the sky must have been exceptionally bright to only be able to get a good histogram at 20s. Maybe it is lights reflecting off of the snow cover.

My objectives were to capture Soul Nebula (IC 1848), and switch to Orion Nebula (M42) when It got above the trees. With M42 I wanted to run a capture with a normal exposure histogram peak at 25-33%, which would expose most of the nebula correctly. I would expect that the bright center would be overexposed. I would then run another capture that was underexposed to capture detail around the bright Trapezium. After stacking, my intent is to use high-dynamic range (HDR) processing techniques to produce a combined image that is not blown out in the bright core.

The temperatures were 27 degrees when I went out the uncover the scope and power up the minicomputer at 1630 (15 minutes); 23 degrees by the time I went back out to polar align, focus, and star align at 1750 (20 minutes); and it was 19 degrees on my final trip out to shut down the scope at 2320 (2 minutes). I got a little chilly during the polar alignment visit to the scope, but it wasn’t too bad. The dew point was below the temperature, which I took to mean a low risk of dew or frost, but since I was using wall power instead of a battery, I turned on the dew heater as a precautionary measure. Winds were very light to completely still.

There were no equipment issues. Everything connected and worked properly. After powering up the mount, I polar aligned with PoleMaster and found that I was about 1/3 degree off, probably because of tripod legs settling. I set my focus with Polaris in the star field and decided that I would not refocus for the rest of the night. I slewed to Capella, which is near my first target, to star align. I found it with in the image frame, so I centered up and synchronized the mount.

While on IC 1848 I was not able to determine if I had the telescope on the target and properly framed, because I could not detect any nebulosity in a single frame, and because I could not match star patterns in the frame with Stellarium. I have fairly high confidence that I was on target because of the close proximity of IC 1848 to my alignment star, and because M42 was perfectly centered after my next slew. I took 58 20s subs at ISO 1600.

I slewed to M42 at around 2025, and had to wait briefly for it to clear the treetops before I began imaging at 2036. For my normally exposed images, I took 240 20s subs at ISO 800. The sky seemed brighter so I had stopped down from ISO 1600 to ISO 800 to get my histogram peak back to about 25%. For my underexposed images, I left the ISO at 800, and took 30 subs at 1s, 2s, and 4s. The reason for taking three sets of underexposed images is that I do not have experience with HDR processing, and therefore I have no idea what amount of exposure is going to work best for the final image.

After shooting M42, I took 25 darks at ISO 800 at durations of 20s, 4s, 2s, and 1s to match the M42 light frames. I should have taken 25 darks at ISO 1600 with a duration of 20s to match the IC 1848 lights.

This morning after it warms up just a little, I will go out to capture some dark frames to go with IC 1848, and capture some flat frames.

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