The week started here with a grim weather forecast, rain, cloud and winds taking us from October to November. Not exactly a surprise here in the UK, but there was a glimmer of clear sky on Sunday 30th Oct. I have fancied revisiting NGC 1499 the California Nebula and so I planned and was set up, polar aligned and yes just ready to capture and clouds swept over like they knew!
This failed imaging session got me thinking about whether I should revise old data and try reprocessing with the new workflow to see what improvements I have made. Looking through my images I did have a single night on the California back in January 19th this year. In Jan this year I was using Deep Sky Stacker and Photoshop. Now it's Siril, Starless processing before heading into Photoshop. If you are interested here's the link to read all about my Post Processing workflow.
On the border of Perseus and Auriga, NGC 1499 or the California nebula named after its resemblance to the American state. Around 1,000 light years away this is fairly large object 2.5º long, although technically this is a magnitude 6 object because it spread over such a wide area it is a very difficult object to see visually. It is glowing because of the large O7 star Xi Persei or Menkib. It is glowing in Hß wavelength and is one of the few stars of this type that can be seen with the naked eye.
The plate solve of the image show Menkib, also the position of an Elliptical Galaxy hidden behind NGC 1499, 279 Million light years away, so yes substantially behind California!
Capture
Three nights spent on this 26th, 29th of December 2022 and a Final night on the 2nd Jan 2023.
All three nights using my usual equipment with the new ZWO ASI533MC Pro with gain of 100 offset 40 and running at -10ºC through the Optolong L-Enhance Filter and 300s exposures.
2022-12-26
Initially clear conditions but around 9pm clouds rolled in with showers so cut short. No Moon.
First light taken 17:32
Last light taken 20:35
Lights - 36
Flats and Dark Flats- 30
2022-12-29
Initially clear conditions although around midnight clouds moved in to draw things to an early finish.
First light taken 17:49
Last light taken 00:09
Lights - 72
Flats and Dark Flats- 30
2023-01-02
Clear although 80% Moon. Finished early as forecast was for showers in the early morning.
First light taken 17:32
Last light taken 23:22
Lights - 67
Flats and Dark Flats- 30
Pre-Processing
175 Images taken over the three nights. Only 1 completely rejected during registration due to full cloud no stars.
Calibration File Processing
As per my earlier blog post on Flats processing I did have some problems with generating the master flats for each of the 3 nights. As per the blog post, I have started to quickly generate statistics for the pre-processed flats (calibrated with the Dark Flats). I have found that when the Median fluctuates significantly (say by 15%) from the average value that it is worth removing that image. In that way you get less rejections during Master Flat stacking.
Pre-Processing Lights
Given the Moon in session 3 (2nd Jan 2023) I ran a Background Extraction across all pre-processed lights (Lights Pre-Processed with the master Flat and the Master Dark). The extraction carefully avoided the nebulosity regions and used a single polynomial algorithm. This generated a new file for each Light frame which was subsequently used as part of registration across all nights.
Registration and Stacking
After eyeballing for quality I decided that the cutoffs out be:-
FWHM < 4.2
Roundness > 0.8
wFWHM < 6.0
In addition given the amount of exposures I wanted to blink through the images to ensure every frame was of a subjective standard. In some cases the statistics did not tell the full story and it was necessary to remove a few additional frames (mostly from the 2nd Jan I believe to the Moon and seeing conditions where not as good as the Christmas nights).
175 images of 300s = 14h35m
After filtering 137 images of 300s = 11h25m
I might measure the ration in the future so for reference that is a rejection of 21.71%
Stacked 137 * 5m -Total Integration Time = 11h25m
Post Processing (Dec 5, 2023)
Siril
Crop - fairly minor to remove stacking artefacts
Background Gradient
Colour Calibration Photometry
Deconvolution, Kernel size of 0.7
Asinh Stretch - 2 iterations with stretches of (30,3)
Histogram Stretch
Green Noise Removal (SNR)
Starless and Stars created using automated Siril scripting to produce 16bit Tiff and pass it through Starnet++ then to obtain the starless and stars version..
Once we have a TIFF (16 bit version) of Starless move into PS.
Photoshop Processing
Levels and Curves - Setting the low and high points to the edges of the data in each channel as part of Levels. Light curve stretches on each channel making sure to not overstretch Blue and Green but overlap with left of Red
Raw - Highlights and Contrast
Raw - Texture (lightly decreased)
Raw - Clarity (lightly increased)
Raw - Colour Contrast - Pushing reds to deeper reds using the red hue, also pushing the orange to Yellow hue this brought out more contrast. This was very subtly done
Raw - Noise Reduction, small Noise and small detail enhancement
Raw - Saturation and Vibrancy and Shadow, small Sat, Vibrancy increases and medium drop in Shadow
Create FIT version of TIFF file output from PS using Siril
Once back from PS then Pixel Math Add the Stars back into the FIT version of the Photoshop processed TIFF file using the formulae (starless+(0.8*stars)).
Created JPG version for my Social feeds and Astrobin.
Results
I really like this object, in my head this has the huge wavefront electoral storm that you might see trying to destroy the Star Trek Enterprise! There is lots of detail to be explored and at my focal length which forces a more zoomed in view gives a very dramatic presentation.
If you have perused my blog you will have seen that this was a target with the old Canon 600D in January 2022 with a reprocessing and blog about this in Nov 2022. In fact that previous post showed the progression in my Processing due to new tooling and also (hopefully) my skill level. I thought I would show the 3 images once again, obviously this recent image was taken with a different camera and therefore the field of view and framing is different.
The first image is 11h25m taken with the new camera (this post)
The second and third image use data taken from January 2022 with my old Modified Canon 600d DSLR, 2h28m. The 3rd image is just to show that my processing is improving.
Putting aside the framing for a moment, it's obvious to me that large amount of additional exposure time (460%) brings much more detail. The image image looks weightier, there is more depth. That is not to say the 2nd image isn't pleasing, I like the wispiness of it giving a "Flame in Space" look and feel.
Framing wise, given the ASI533MC Pro's physical 1" size and the smaller pixel size than the 600D's APS-C based sensor there is a dramatic difference. I actually like both and this object was one of those in my Camera Comparison blog that I knew I would not be unable to get the whole subject in one frame. I like the framing of both, they offer the floating flame in the vast blackness of space versus the Star Trek Enterprise Electric Storm wavefront vibe.
Anyway all the best and Happy New Year everyone and clear skies....now what object next!