IC 5070 is a subject I have grabbed before using a slightly wider field of view to grab it and the more often photographed American Nebula (NGC 7000). Here is that shot from back on a very hot August night in 2022. It was taken with my uncooled but astro modified Canon 600D.
Looking back at this, boy is it noisy and is the typical red cloudy shots of both of these objects, although IF your eyes were able to observe and retain memory of all the photos hitting them then this is actually what it would look like, there is far more Hydrogen than any other element in the Universe and it emits red light when excited.
This new capture was performed at the back end of August and early September and given my new focal ratio with my cooled astro camera it is going the field of view was not going to be big enough to replicate last years shot. I had already spent many nights on my the North America nebula so time to focus (pun intended) on the Pelican. My main goal was not to have this turn into a red cloud picture, but to bring out more of the other colours and try and increase the detail.
Capture
Three nights using the l-Enhance filter with a total imaging time of 246*5m = 20h30m.
Here's the breakdown together with the Flats and Darks taken each morning:-
2023-08-29
79 Images taken (300s) through l-Enhance Filter
30 flats
30 dark flats used as bias
2023-09-03
77 Images taken (300s) through l-Enhance Filter
30 flats
30 dark flats used as bias
2023-09-04
90 Images taken (300s) through l-Enhance Filter
30 flats
30 dark flats used as bias
Pre-Processing
I initially ran through my usual workflow to calibrate the lights and register a single RGB image.
RGB processing
The usual multi night calibration:-
For Each night (choose a sequence offset, 01000, 02000...)
Stack Dark Flats (No Normalisation)
Calibrate Flats using Dark Flats as a Bias
Check for out-of-band Flats (using the mean of the Median of each Flat) and remove those flats
Stack the calibrated Flats (Multiplicative normalisation)
Calibrate Lights using my library of master Darks selecting the one for this session of 5m duration at 100 gain and 40 offset at -10º C, and the Stacked Flats, debayer the lights also during this process
Move these lights to my multisession folder, making sure not to overwrite other lights (hence setting a different sequence offset each night)
Now we go for registration and quality control filtering. In this case the following criteria was used:-
Removed 12 Roundness < 0.75
Removed 1 FWHM>3.5
Removed 16 wFWHM>5
Eyeballed and removed small number of frames that had significant movement from the reference (too much drift)
Removed 5 with outlining background noise issues
Removed 10 with outlying few stars detected.
This left 170 out of the starting 246 light frames.
170 * 5m = 14h10m Integration time
Post Processing RGB
In summary:-
Crop stacking artifacts
Run Photometric Colour Calibration on the Stars
Go Starless and Create a Mask (allowing Siril to automatically lightly stretched the data automatically)
ASinH stretch the stars to get them to the intensity I want. I used this method rather than the deconvolution method as I think it delivers a result without the artefacts that Deconvolution often delivers (such as rings around stars).
On the Starless I ran:-
Generalised Hyperbolic Stretch
Took into Photoshop and ran Camera RAW filters to modify decrease the highlights and increase the contrast
Reduce the Texture and Increase the Clarity
Ran Noise Reduction (used PS own not the Xterminator previous - need to buy licence!)
Saved back and combined with the Star mask
Saved FITS results and JPG for social media.
Ha-OIII (HOO) Dual Band Filter Processing
Very similar to the RGB process with the exception that we do not debayer the calibrated lights and we add a step in Siril to extract the Ha and OIII.
For Each night (choose a sequence offset, 01000, 02000...)
Stack Dark Flats (No Normalisation)
Calibrate Flats using Dark Flats as a Bias
Check for out-of-band Flats (using the mean of the Median of each Flat) and remove those flats
Stack the calibrated Flats (Multiplicative normalisation)
Calibrate Lights using my library of master Darks selecting the one for this session of 5m duration at 100 gain and 40 offset at -10º C, and the Stacked Flats
Run seqextract_HaOIII 'pp_lights'
There are now two sequences from the lights, one for Ha and one for OIII.
These two sequences are kept seperate but are copied, as per the RGB processing example to a single Multi-session folder for registration.
Registration is performed separately for Ha sequence files and OIII sequence files. The same filtering process was used on both as per the RGB, so the same Integration time of around 14h was left to be stacked, stacking performed resulting in Ha result and an OIII result image.
Post Processing HOO
The following diagram how the post processing workflow I used for the HOO. To emphasise the point that during the stretching with Generalised Hyperbolic Stretch function in Siril I was very conservative. If at the Ha and OIII steps the images are too light then when it comes to the combination of the layers using the Screen blend method the result will be very washed out. The selection of the Red hue and the Blue /Cyan hue for the OIII has a big impact on the final blended image.
Results
To be honest the HOO result needed a couple of attempts and I am still a little dissappointed with it. I think my expectation was that there would be greater separation of the Blues and Reds, in stead what I got was more a white with a hint of the blue coming from the OIII. In hindsight this may have been to do with this subject having a fairly ctrong signal across Ha and OIII that overlapped. I think other targets may respond better to the HOO treatment than this.
The first image is the RGB second is HOO
More practice needed with the HOO, I am also thinking that a tighter pass of OIII and Ha emission lines might produce better results. The Optolong L-Extreme is one such filter...