Overview

I was excited for the first clear night in weeks. I got everything set up and took about 40 light frames over 3.5 hours. That seemed fine, until I tried to process them all.

Equipment Issues

About half-way through, I saw images that started coming in as just long star trails. I happened to have just increase the exposure time, so I thought that had something to do with it. It turns out that my telescope had gotten caught on the power supply brick that I had clamped to the tripod leg. Once I moved that down I was back in business.

This also gave me a chance to do a meridian flip. Sounds routine, but it could be the first time I did that.

Composing Troubles

I tried to get all of the veil nebula captured in one frame. It is fairly large, and has a couple of areas of interest. It just barely fits in my camera/lens resolution, so after everything was stacked, the interesting parts were way on the edges of the resulting image. Next time I won’t be quite so ambitious and focus on one part at a time.

There was some light pollution on the edges, but since the subjects stretched all the way to the edge, there was not much I could do about it. I just need to center the object better, which should be easy with plate solving.

Calibration Issues

I thought I would save some time by just re-using the calibration frames from last time. What I didn’t realize is that those frames had some problems, which made all the calibration frames pretty much useless.

Dark Frames

First off, I found that my stacked dark frames looked like this:

dark_stacked.png

I guess they were not that dark and I had some light leaking in. I’m not exactly sure how that happened, but it makes these frames useless.

Update: This is caused by Amp Glow

Flat

Then I found out that my flat frames were not very flat. One corner was much darker than the rest of the image, so I must have not done this process correctly either. And there looks to be a lot of dust on my lens, which is embarrassing.

flat_stacked.png

Siril Post-Processing / Output

As a quick first step, I tend to do the same things in Siril for most of my images. It turns out that the order I do these in makes a big difference. Here are some comparisons

Base Image (cropped)

test0-base.png

I would typically do Deconvolution as well, but I’ll skip that step for this experiment.

Flow 1

Steps:

  1. Background Extraction
  2. Remove Green Noise (no/little impact after background extraction)
  3. Photometric Color Calibration

test1.png

Flow 2

Steps:

  1. Remove Green Noise
  2. Background Extraction
  3. Photometric Color Calibration

test2.png

Flow 3

Steps:

  1. Photometric Color Calibration - FAIL

I think the base image has so much interference that the plate solving does not work

Flow 4

Steps:

  1. Remove Green Noise
  2. Photometric Color Calibration
  3. Background Extraction

test4.png

Output

For this image I liked the “Flow 2” one above as a starting point. From there I did some Asinh stretching and saturation changes.

I don’t love the result, but I will keep working on it.

output.jpg