M42 and NGC253
We had a (near miraculous) clear night here, so I had the rig outside to have another crack at imaging with the new camera.
Overall, I was happier with the results. Although I dropped the exposure time down to a mere 10 seconds, the ‘183MC-Pro is still picking up a lot of blue light pollution. In Siril, the blue channel is almost swamped with it, and the RGB image is a vivid blue.
I can only presume that it’s caused by the light pollution in my street / suburb. The streetlights are the ultra-bright LEDs, and even though I’m imaging from a location that blocks the direct light from the street lights, I am still imaging through their “light cloud” - especially when my target is relatively low to the horizon.
I fear it might be time to invest in a filter drawer and a dual-band filter designed for use with OSC cameras. This would chop out a lot of the light pollution, as the filter only allows Ha (Hydrogen-alpha) and Oiii (Oxygen-three) wavelengths through. Because it chops a lot of light out, I would be able to run longer exposures and capture more of the fainter detail that is currently being lost within the noise.
The primary target for the evening was NGC253. It’s also known as the “Sculptor Galaxy” due it’s being within the constellation ‘Sculptor’.
As a bonus, I realised that Orion was visible for the first time since January or February of this year. I was running out of time (the joys of imaging during the week when I have work the next morning…) so was only able to get a very tiny amount of data. In this case, it was a whole 10 minutes. Even with such a minuscule amount of data, I was amazed at the amount of detail the camera captured. Of course, the central core of the nebula is over-exposed. M42 is a difficult target to capture, and most astrophotographers will capture two sets of data - one for the detail in the nebulosity, the second (much shorter exposure times) for the central core.
As is my usual process, I stacked the images (along with the requisite calibration frames) in both Siril and Affinity Photo. I then processed the stacked output to arrive at a final image that I was pleased with. (OK, let’s be honest here - I’m not totally pleased with how much noise is visible when I go pixel-peeping.) The final images are below, and show the differences caused by different stacking software.
I also tried my hand at using Ekos’ automatic flats generator. I do need to test it further, as I had very little success with it. I selected an ADU of 32000 (as suggested by users of the CloudyNights forum), but Ekos kept bounding between 29k and 41k. It did manage to capture a couple of frames, with an exposure time of 0.225 seconds. I figured this would be close enough, and manually captured a series of frames with this settings. Sadly, they were under exposed; which reduced their ability to remove any vignetting in the light frames or dust in the optical train.
The standard formula for calculating the ADU is (2^(camera bit depth) / 2) - for the 183MC-Pro it should be (2^14 / 2), or 8192. I’ll give this a try next time I am imaging and (hopefully) will have much better results.
Image details:
- Gain: 25
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 10 seconds
- Lights: NGC253 - 300, M42 - 60
- Darks: 40
- Flats: 40 (underexposed, so not as useful as they should have been)
- Bias: 44
- Stacked and pre-proc’d in SiriL, finished in Affinity Photo
Working solely within Affinity Photo here and with a slight crop to increase the size of the galaxy. This is reasonably close to the common image of the galaxy - a bright, almost silver disk with mottled patches of dark dust in the spiral arms.
NGC253 - (Affinity Photo)
This is using the stacked data from Siril, and without the crop to remove the excessive amount of space around the galaxy. No matter what I tried, I wasn’t able to remove that yellow / brown tinge to the galaxy. Trying to get it bright just blew up the noise.
NGC253 - (Siril)
Not much to say here, really. Stacked and processed solely in Affinity.
M42 - The Orion Nebula (Affinity Photo)
In comparison to the Affinity-stacked image, the Siril image has much greater detail within the dust and gas clouds of the nebula, with much better colour contrast.
I employed the Siril ‘OSC with drizzle’ script for this image, resulting in a 2x magnification of the light frames during the stacking procedure - which I then had to scale back down during processing. ‘Drizzle’ is used to enhance fine data, and it looks like it really worked here.
