August 19
The router I talked about in my last post worked well, and I should be able to monitor my imaging remotely from now on. Other things happened this night that made it less than successful.
Imaging started with NINA doing a slew, center and rotate, or trying to. I use NINA's manual rotator, which has always worked well for me in the past. This night it did not. My first rotation resulted in NINA requesting an even greater rotation in the same direction, and so did the next. I didn't want to sort it out, the image wasn't going to amount to much given the omnipresent overhead smoke, so I redid the sequencer script to just slew and center and pause so I could do a rotation by eyeball. Not at all optimal but it started the collection of light frames.
After a while I noticed that the images were coming in fuzzy-looking. It wasn't a focus issue; the stars were sharp but diffuse. It was a very dewy night so that was my first guess. I put everything on pause and looked at the objective. It was dry. I could have examined all the other optical surfaces but instead I looked at the camera settings. The camera was at the correct temperature (-5 C) but the dew heater on the sensor window was off. I set it back on and decided to wait and see if it would clear; I could monitor this on my tablet indoors. The images slowly improved, but I was running out of time. I decided to call it a night and started breaking down the setup.
The next afternoon I found that there was a setting in the manual rotator that allowed me to reverse the sense of corrections. Having it set the wrong way would have produced exactly the symptoms I saw the night before, so I was confident that things would work next time.
Both issues were probably a consequence of my having to restore NINA after a full lobotomy of my laptop earlier this year; the clean reinstall had put everything back to default settings.
August 20
So, two problems, both probably fixed, and a clear night. The moon was at first quarter and there was way too much overhead smoke, but I wanted to see if things were fixed so out I went to the club's Eagle Lake site. Everything worked and I decided to do a quick and dirty two-pane mosaic of the Veil Nebula. I had planned for a minimum of two hours, one for each pane, and started collecting light frames. The northern pane finished with 60 x 60 s frames, then the sequencer did its thing and went to the southern pane. 45 frames into that the clouds swept in and the night was over; the second pane got short-changed.
An hour per pane was not really enough to for a decent image, but it did give me data to practice mosaic-making. Here is the result:
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| Veil Nebula 2-Pane Mosaic (1/2 scale, click to enlarge) |
Comments:
- This needs more time on target!
- Shooting 60 s subs really helps preserve star color and allows essentially total eradication of satellite tracks, Yay!
- I would like to thin out the stars better during the next reprocess.
- About that lighter area to the right of the Western Veil: is it real or is it an artifact of how I flattened the field? It compares very well to this image in which it shows structure; there's also a discussion (and another excellent picture in RGB) of it on CloudyNights. Since the veil is often imaged using LP filters or in narrowband, most images might not show a dim broadband feature like this. I'm pleased that I'm able to draw it out with only an hour of imaging!
- The image was calibrated using dark frames, flats, and flat darks. Lights were dithered, but not sufficiently for drizzling. I had about a half dozen runs at processing this before I found a good way to merge the panes. The workflow I found that worked best is given below.
- Can you find the two seams? I can't despite knowing right where they are!
- [Added 8/28/2026] Three separate cropping operations (see workflow below) reduced the mosaic down from its maximum possible size of 6248 x 7308 (taking into account the original 25% overlap) to 5980 x 7076. That's a loss of 7.9 percent in terms of area, or about 3.8% linear loss. Not too bad, but I'm glad I started with 25% overlap and had room to spare surrounding the Veil.
August 22
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| Cocoon Nebula (1/2 scale, click to enlarge) |
Mosaic Workflow
Use the ImageSolver script to solve the images and give them the solutions.
The Veil field is packed full of stars to the extent that I considered using DynamicBackgroundExtraction to be iffy, so I used AutomaticBackgroundExtractor with degree set to 1 and the subtraction as the correction. Why degree 1? This eliminates the mean and gets rid of the overabundance of green often seen in One-shot color masters along with the field-uniform light pollution. During relatively brief imaging sessions, the light pollution may also have a significant spatially linear component, so that's removed, too.
The pane backgrounds must be matched, so use DNALinearFit. This can be obtained at David Ault's website, and more specifically here.
Merge the newly cropped panes using GradientMergeMosaic with type of combination = overlay, Shrink radius = 1, Feather radius = 10, and Blackpoint = 0. If you see pinched stars, you can rerun it with an increased feather radius or you can black out offending stars. At this point you will have a merged mosaic image we will call MyMosaic.
Stars image: the usual STF-HT method wildly overstretched the stars, so I used StarStretch with the stretch amount = 4 and color boost = 2. The stretch amount is where you can get very fiddly. It's worth exploring the entire stretch range of 4 to 6.











