The Eye of God 

Since my "The Eye of God" won the Astronomy Photographer of the Year 2022 (Stars and Nebulae) last year, I keep going to dig all the faint signal around the NGC7293. Combined data from 2021 to 2022, I have got 95 hours SHO data from 0.5meter f/3.8 Newtonian, and 11.5 hours HOO data from 1 meter f/6.8 RC. They're all Chilescope telescopes. It's my first time to collect more that 100 hours data with >0.5m telescopes and my first time to reveal Sii data of the Helix nebula. The Sii data is extremely faint that can't find a usable reference image and now I bring maybe the deepest Sii exposure of Helix nebula. Hope you enjoy my major work in 2022.

T2+T3: 95h
Ha=50*1800s
Oiii=64*1800s
Sii=76*1800s

T1: 11.5h
Ha=9*1800s
Oiii=14*1800s

The  22.5 hours winner image was not the upper limit of the NGC7293. I'm not satisfied with the core details and surrounding nebulae SNR. Besides, There are something in the Sii channel but the SNR was quite low in 10 hours data last year that I can't do anything with it. So I spent more time to capture SHO via Chilescope T2+T3 and use T1 for those core details. The results are exciting.
1.[Wide field looking] The surrounding low SNR details gain a lot with much more exposure with T2T3
2.[Wide field looking] The Sii data become useful after collecting 38 hours exposure.
3.[High resolution] The T1(one meter RC) really shows the great detail of those cometary knots

But here comes the challenges:
[Challenge.A] Combining the Ha and Oiii data from T1 and T2T3, their brightnesses are quite different.
[Challenge.B] Rework the colors and try to show all the faint details with new data, make it similar to the winning image last year. The HDR and color processing are relevant and very difficult.
[Challenge.C] Adding the Sii data to the image.


## Challenge.A
The data from  f/3.8 is much brighter than the data from f/6.8 RC, although the T1 wins the aperture. And they're sampling at 0.96"/px and 0.273"/px, quite different. So the first thing to do is interpolate the 0.96"/px data to 0.273"/px. Image Solver(Gaia DR3 complete database with distortion) and Mosaic by Coordinates(used for alignment and interpolation) did it. So now the data from two sets are only different from brightness and the same pixel scale will help the statistic and calculation. With the same pixel scale, and after remove stars by SXT, I can do the linear fit only for the nebula on the same FoV of these two sets of data. Of course I did accurate background modelization on T2T3 data.

The results showing that T2H = 5.258* T1H +0.00086, T2O = 5.1638* T1O +0.00036. With the linear fit data, I can raise the brightness of the T1 data to the same "average" brightness of T2T3 data. Then I can use a core mask to combine two data sets. Taking the outstanding surrounding data from T2T3 and high resolution core details from T1.


##Challenge.B
During the processing, I found the most difficult part of processing the Helix nebula with fast scope is that the Helix core is much brighter than the surrounding faint details. That leads to proper HDR is needed. But pay attention to the colors and details  in core regions, I need to keep wonderful color and high resolution data of cometary knots while doing HDR. I would say this is an order-dependent issue. HDR first or adjust color first will change all the things.

##Challenge.C
Even what's Sii look like is unknown, let alone how to play with it. I can find a satisfied reference to see how to add Sii data in HOO combination. After some attempts, I decided to add limited Sii data in the core as yellow clouds above the blue ocean. Still worth thinking how to use it.